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Keithley 2750 Service Manual

Keithley 2750 Service Manual

Multimeter/switch system
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Model 2750 Multimeter/Switch System
Service Manual
©2015, Keithley Instruments
All rights reserved.
Cleveland, Ohio, U.S.A.
Second Printing, August 2015
Document Number: 2750-902-01 Rev. B

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  • Page 1 Model 2750 Multimeter/Switch System Service Manual ©2015, Keithley Instruments All rights reserved. Cleveland, Ohio, U.S.A. Second Printing, August 2015 Document Number: 2750-902-01 Rev. B...
  • Page 2 Revision A (Document Number 2750-902-01).............. March 2001 Revision B(Document Number 2750-902-01) .............. August 2015 All Keithley product names are trademarks or registered trademarks of Keithley Instruments, Inc. Other brand names are trademarks or registered trademarks of their respective holders.
  • Page 3 Only properly trained service personnel may perform installation and service procedures. Keithley products are designed for use with electrical signals that are rated Installation Category I and Installation Category II, as described in the International Electrotechnical Commission (IEC) Standard IEC 60664.
  • Page 4 To maintain protection from electric shock and fire, replacement components in mains circuits, including the power transformer, test leads, and input jacks, must be purchased from Keithley Instruments. Standard fuses, with applicable national safety approvals, may be used if the rating and type are the same. Other components that are not safety related may be purchased from other suppliers as long as they are equivalent to the original component.

  • Page 5: Table Of Contents

    Calculating resistance reading limits ........Restoring factory defaults ............Performing the verification test procedures ....... Verification test summary ........... Test considerations .............. Model 2750 verification ............. Verifying DC voltage ............Verifying AC voltage ............1-10 Verifying DC current ............1-11 Verifying AC current ............
  • Page 6 Front panel calibration code ..........Remote calibration code ............Comprehensive calibration ............Calibration cycle ..............Recommended equipment ........... Aborting calibration ............Front panel calibration ............Remote calibration ............2-14 Manufacturing calibration ............2-20 Recommended test equipment .......... 2-20 Extender board preparation ..........2-20 Unlocking manufacturing calibration ........
  • Page 7 Power supply ............... Display board ..............Digital circuitry ..............Analog circuitry ..............Troubleshooting ............... 4-14 Display board checks ............4-14 Power supply checks ............4-14 Digital circuitry checks ............. 4-15 Analog signal switching states .......... 4-16 No comm link error ..............4-24 Disassembly Introduction ................
  • Page 8 DC voltage, DC current, and resistance: ......AC voltage and AC current: ..........Temperature: ............... Optimizing measurement speed ..........DC voltage, DC current, and resistance: ......AC voltage and AC current: ..........Temperature: ............... Calibration Reference Introduction ................Command summary ..............Miscellaneous calibration commands ........
  • Page 9 List of Illustrations Performance Verification Figure 1-1 Connections for Model 2750 DC volts verification ....Figure 1-2 Connections for Model 2750 AC volts verification .... 1-10 Figure 1-3 Connections for Model 2750 DC current verification ..1-12 Figure 1-4 Connections for Model 2750 AC current verification ..
  • Page 10 Digital circuitry block diagram ..........Figure 4-3 Analog circuitry block diagram ........... 4-10 Figure 4-4 Simplified schematic of dry circuit ohms ......4-13 Disassembly Replaceable Parts Accuracy and Optimization Calibration Reference Calibration Program Figure C-1 Model 2750 calibration program ...........
  • Page 11 ACI limits ................1-13 Table 1-6 Limits for normal resistance verification ......1-16 Table 1-7 Limits for Model 2750 dry resistance verification ....1-18 Table 1-9 Four-wire RTD temperature verification reading limits ..1-19 Table 1-8 Thermocouple temperature verification reading limits ..
  • Page 12 Table 5-2 Power module wire colors ............Replaceable Parts Table 6-1 Model 2750 motherboard parts list ........Table 6-2 Model 2750 display board parts list ........6-12 Table 6-3 Model 2750 backplane board parts list ........ 6-13 Table 6-4 Model 2750 miscellaneous parts list ........

  • Page 13: Performance Verification

    Performance Verification...

  • Page 14: Introduction

    Performance Verification Model 2750 Multimeter/Switch System Service Manual Introduction Use the procedures in this section to verify that Model 2750 Multimeter/Switch System accuracy is within the limits stated in the instrument’s one-year accuracy specifications. You can perform these verification procedures: •...

  • Page 15: Verification Test Requirements

    • A relative humidity of less than 80% unless otherwise noted. Warmup period Allow the Model 2750 to warm up for at least two hours before conducting the verifica- tion procedures. If the instrument has been subjected to temperature extremes (those outside the ranges stated above), allow additional time for the instrument’s internal temperature to stabilize.

  • Page 16: Recommended Test Equipment

    Note: The Fluke 5725A amplifier is necessary only if you wish to verify the 750V AC range at 50kHz and 3A AC and DC current ranges at 3A. Verification at 220V, 50kHz, and 2.2A on the current ranges using only the 5700A calibrator is adequate for most applications. Calibrator 1 uncertainty is not four times better than Model 2750 1 range accuracy.

  • Page 17: Verification Limits

    The following is an example of how reading limits have been calculated. Assume you are testing the 10V DC range using a 10V input value. Using the Model 2750 one-year accu- racy specification for 10V DC of ± (30ppm of reading + 5ppm of range), the calculated limits are: Reading limits = 10V ±...

  • Page 18: Restoring Factory Defaults

    ENTER. Performing the verification test procedures Verification test summary Verification tests can be performed either through the Model 2750 front panel terminals or through plug-in modules. This section contains the following procedures: • Model 2750 verification — Use this procedure to test Model 2750 accuracy through the front panel terminals.

  • Page 19: Test Considerations

    Do not use autoranging for any verification tests because autorange hysteresis may cause the Model 2750 to be on an incorrect range. For each test signal, you must manually set the correct range for the Model 2750 using the range keys.

  • Page 20: Model 2750 Verification

    Perform these tests to verify accuracy using the Model 2750 front panel terminals. Verifying DC voltage Check DC voltage accuracy by applying accurate voltages from the DC voltage calibrator to the Model 2750 INPUT jacks and verify that the displayed readings fall within speci- fied limits. CAUTION Do not exceed 1000V peak between front terminals INPUT HI and INPUT LO because instrument damage may occur.
  • Page 21 Note: Use shielded, low-thermal cables for 100mV and 1V ranges. Select the DC volts function by pressing the DCV key, and set the Model 2750 to the 100mV range. Set the calibrator output to 0.00000mV DC, and allow the reading to settle.

  • Page 22: Verifying Ac Voltage

    Model 2750 Multimeter/Switch System Service Manual Verifying AC voltage Check AC voltage accuracy by applying accurate AC voltages at specific frequencies from the AC voltage calibrator to the Model 2750 inputs and verifying that the displayed readings fall within specified ranges. CAUTION Do not exceed 1000V peak between front terminals INPUT HI and INPUT LO, or 8 ...

  • Page 23: Verifying Dc Current

    Verifying DC current Check DC current accuracy by applying accurate DC currents from the DC current cali- brator to the AMPS input of the Model 2750 and verify that the displayed readings fall within specified limits. Follow these steps to verify DC current accuracy:...
  • Page 24 AMPS Amps Note: Be sure calibrator is set for normal current output. Set the Model 2750 for the 20mA range. Source positive and negative full-scale currents for each of the ranges listed in Table 1-4, and verify that the readings for each range are within stated limits.

  • Page 25: Verifying Ac Current

    Check AC current accuracy by applying accurate AC voltage current at specific frequen- cies from the AC current calibrator to the Model 2750 input, and verify that the displayed readings fall within specified limits. Follow these steps to verify AC current:...

  • Page 26: Verifying Normal Resistance

    Follow these steps to verify resistance accuracy: Using shielded, Teflon-insulated or equivalent cables in a 4-wire configuration, connect the Model 2750 INPUT and SENSE jacks to the calibrator as shown in Figure 1-5. Be sure the INPUTS switch is in the FRONT position.
  • Page 27 Select the Model 2750 4-wire resistance function by pressing the 4 key, then choose the SLOW integration rate with the RATE key. Set the Model 2750 for the 1 range, and make sure the FILTER is on. Enable OCOMP (offset-compensated ohms) by pressing SHIFT then OCOMP. (Use OCOMP for 1, 10, and 100...

  • Page 28: Verifying Dry Circuit Resistance

    100M 99.7970 to 100.2030M __________ to __________ M * Enable OCOMP (offset-compensated ohms) when testing 1, 10, and 100 ranges. ** Calculate limits based on actual calibration resistance values and Model 2750 one-year resistance accuracy specifications. See “Verification limits.” Verifying dry circuit resistance Check the dry circuit resistance function by connecting accurate resistance values to the Model 2750 and verifying that its resistance readings are within the specified limits.
  • Page 29 Select the Model 2750 dry circuit resistance function by pressing SHIFT then DRYCKT. Set the Model 2750 for the 1 range, and make sure the FILTER is on. Enable OCOMP (offset-compensated ohms) by pressing SHIFT then OCOMP. (Use OCOMP for 1, 10, 100, and 1k range verification.) Enable line sync ON by pressing SHIFT then LSYNC.

  • Page 30: Verifying Temperature

    0.999510 to 1.000490k __________ to __________ k * Enable OCOMP (offset-compensated ohms) when testing 1, 10, 100, and 1k ranges. ** Calculate limits based on actual calibration resistance values and Model 2750 one-year dry circuit resis- tance accuracy specifications. See “Verification limits.”...
  • Page 31 Figure 1-5 similar connecting scheme.) Be sure the INPUTS switch is in the FRONT position. Configure the Model 2750 temperature function for °C units and RTD temperature sensor (=0.00385) as follows: Press SHIFT then SENSOR, and note the unit displays the temperature units: UNITS: C.

  • Page 32: Verifying Frequency

    Set the function generator to output a 1kHz, 1V RMS sine wave. Select the Model 2750 frequency function by pressing the FREQ key. Verify that the Model 2750 frequency reading is between 999.9Hz and 1.0001kHz. Figure 1-8 Connections for Model 2750 frequency verification...

  • Page 33: Verifying Dc Voltage

    Model 7700 for 100mV and 1V ranges. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 34: Verifying Ac Voltage

    1-22 Performance Verification Model 2750 Multimeter/Switch System Service Manual Table 1-10 Plug-in module DCV reading limits Range Applied DC Voltage* Reading Limits (1 year, 18° to 28°C) 100mV 100.0000mV 99.9935 to 100.0065mV 1.000000V 0.999963 to 1.000037V 10.00000V 9.99965 to 10.00035V 100V 100.0000V...
  • Page 35 Performance Verification 1-23 Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 36: Verifying Dc Current

    Figure 1-11. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 37: Verifying Ac Current

    Figure 1-12. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 38: Verifying Normal Resistance

    Figure 1-13. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 39: Figure 1-13 Connections For Model 7700 Resistance Verification (1 To 10M Ranges)

    Figure 1-14. Disable external sense on the calibrator. Set the Model 2750 for the 100M range. Source a nominal 100M resistance value, and verify that the reading is within calculated limits for the 100M range. Press the OPEN key to open Channel 1.

  • Page 40: Verifying Dry Circuit Resistance

    100M 99.5770 to 100.4230M __________ to __________ M * Enable OCOMP for 1, 10, and 100 ranges. ** Calculate limits based on actual calibration resistance values and Model 2750 one-year resistance accuracy specifications. See “Verification limits.” Verifying dry circuit resistance Check the dry circuit resistance function by connecting accurate resistance values to the Model 2750 and verifying that its resistance readings are within the specified limits.
  • Page 41 Performance Verification 1-29 Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power, and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.
  • Page 42 Performance Verification Model 2750 Multimeter/Switch System Service Manual Set the Model 2750 for the 1 range, and make sure the FILTER is on. If previ- ously disabled, enable OCOMP (offset-compensated ohms) by pressing SHIFT then OCOMP. (Use OCOMP for 1, 10, 100, and 1krange verification.) Enable line sync (press SHIFT then LSYNC).

  • Page 43: Verifying Temperature

    Model 2750 Multimeter/Switch System Service Manual Performance Verification 1-31 Verifying temperature Thermocouple, thermistor, and RTD temperature readings are derived from DC volts and resistance measurements respectively. For that reason, it is not necessary to independently verify the accuracy of temperature measurements. As long as the DC volts and resistance functions meet or exceed specifications, temperature function accuracy is automatically verified.
  • Page 44 Performance Verification Model 2750 Multimeter/Switch System Service Manual Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.
  • Page 45 Figure 1-14 for similar connecting scheme.) Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 46: Verifying Frequency

    (Figure 1-17). Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for one hour before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.

  • Page 47: Verifying Ratio And Average

    Figure 1-18. Install the Model 7700 in Slot 1 of the Model 2750, then turn on the power and allow the unit to warm up for two hours before proceeding. Be sure the front panel INPUTS switch is set to the REAR position.
  • Page 48 1-36 Performance Verification Model 2750 Multimeter/Switch System Service Manual...

  • Page 49: Calibration

    Calibration...

  • Page 50: Introduction

    A relative humidity of less than 80% unless otherwise noted. Warmup period Allow the Model 2750 Multimeter/Switch System to warm up for at least two hours before performing calibration. If the instrument has been subjected to temperature extremes (those outside the ranges stated above) allow extra time for the instrument’s internal temperature to stabilize.

  • Page 51: Calibration Considerations

    Make sure the calibrator is in OPERATE before you complete each calibration step. • Always let the source signal settle before calibrating each point. • If an error occurs during calibration, the Model 2750 will generate an appropriate error message. See Appendix B for more information. WARNING Observe the following safety precautions when performing these tests: •...

  • Page 52: Calibration Code

    Confirm the code by pressing ENTER. The Model 2750 allows you to define a new calibration code. Use the up and down range keys to toggle between yes and no. Choose N if you do not want to change the code.

  • Page 53: Comprehensive Calibration

    In general, equipment uncertainty should be at least four times better than corresponding Model 2750 specifications. Table 2-1 Recommended equipment for comprehensive calibration...

  • Page 54: Aborting Calibration

    • Setting calibration dates Preparing the Model 2750 for calibration Turn on the Model 2750, and allow it to warm up for at least two hours before per- forming a calibration procedure. Start the calibration process as follows: Access the calibration menu by pressing SHIFT then TEST, then display TEST: CALIB using the up or down range key.
  • Page 55 AC voltage and AC current calibration. Front panel short and open calibration At the Model 2750 prompt for a front panel short, do the following: Connect the Model 8610 low-thermal short to the instrument front panel INPUT and SENSE terminals as shown in Figure 2-1.
  • Page 56 DC volts calibration After the front panel short and open procedure, the unit will prompt you for the first DC voltage: +10V. Do the following: Connect the calibrator to the Model 2750 as shown in Figure 2-2. Wait three min- utes to allow for thermal equilibrium before proceeding.
  • Page 57 If your calibrator cannot output the values recommended in Table 2-3, use the left and right arrow keys, and the up and down range keys to set the Model 2750 display value to match the calibrator output voltage. Table 2-3...
  • Page 58 Set the calibrator to the indicated value, and place the unit in operate. (If the calibrator cannot output the exact resistance value, use the Model 2750 left and right arrow keys and the range keys to adjust the Model 2750 display to agree with the actual calibrator resistance.) •...
  • Page 59 After the 1M resistance point has been calibrated, the unit will prompt you to apply 10mA. Follow these steps for DC current calibration: Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.
  • Page 60 Calibration Model 2750 Multimeter/Switch System Service Manual AC voltage calibration Follow these steps for AC voltage calibration: Connect the calibrator to the Model 2750 INPUT HI and LO terminals as shown in Figure 2-4. Figure 2-4 Connections for AC volts calibration...
  • Page 61 After the 700VAC at 1kHz point has been calibrated, the unit will prompt you for 100mA at 1kHz. Follow these steps for AC current calibration: Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3.

  • Page 62: Remote Calibration

    RS-232 port using a straight-through 9-pin to 9-pin cable (use a 9-25-pin adapter if necessary). Turn on the Model 2750, and allow it to warm up for at least two hours before per- forming calibration. Make sure the primary address of the Model 2750 is the same as the address speci- fied in the program that you will be using to send commands.
  • Page 63 Keep drafts away from low-thermal connections to avoid thermal drift, which could affect calibration accuracy. Send the following command: :CAL:PROT:DC:STEP1 After the Model 2750 completes this step, remove the low-thermal short, and then send this command: :CAL:PROT:DC:STEP2 NOTE Be sure to minimize movement near front input terminals. Excessive movements can cause capacitive coupling errors, which could affect calibration accuracy.
  • Page 64 • Send the indicated programming command. (Change the command parameter if you are using a different calibration resistance than that shown.) • Wait until the Model 2750 completes each step before continuing. Table 2-9 Resistance calibration programming steps Calibration Calibrator...
  • Page 65 2-17 DC current calibration After the 1M resistance point has been calibrated, follow these steps for DC current calibration: Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3. Perform the calibration steps listed in Table 2-10.
  • Page 66 Calibration Model 2750 Multimeter/Switch System Service Manual AC voltage calibration Follow these steps for AC voltage calibration: Connect the calibrator to the Model 2750 INPUT HI and LO terminals as shown in Figure 2-4. Perform the calibration steps summarized in Table 2-11.
  • Page 67 Model 2750 Multimeter/Switch System Service Manual Calibration 2-19 AC current calibration Follow these steps for AC current calibration: Connect the calibrator to the AMPS and INPUT LO terminals of the Model 2750 as shown in Figure 2-3. Perform the calibration steps summarized in Table 2-12.

  • Page 68: Manufacturing Calibration

    2-20 Calibration Model 2750 Multimeter/Switch System Service Manual Manufacturing calibration The manufacturing calibration procedure is normally performed only at the factory, but the necessary steps are included here in case the unit is repaired, and the unit requires these calibration procedures.

  • Page 69: Unlocking Manufacturing Calibration

    Perform the entire front panel comprehensive calibration procedure discussed ear- lier in this section. (See “Comprehensive calibration” earlier in this section.) Connect the function generator to the Model 2750 front panel INPUT jacks as shown in Figure 2-5. Select the front input jacks with the INPUTS switch.

  • Page 70: Remote Manufacturing Calibration

    2-22 Calibration Model 2750 Multimeter/Switch System Service Manual Figure 2-5 Function generator connections for manufacturing calibration Function Generator BNC-to-Dual Model 2750 Banana Plug Front Panel Adapter SENSE INPUT Ω 4 WIRE 350V 1000V PEAK PEAK 50Ω Coax 500V PEAK INPUT...

  • Page 71: Model 7700 Calibration

    (See “Comprehensive calibration” earlier in this section.) Connect the function generator to the Model 2750 INPUT jacks as shown in Figure 2-5. Select the front input jacks with the INPUTS switch. Set the generator to output a 1V RMS, 3Hz sine wave, then send the following command: :CAL:PROT:AC:STEP14 <Cal_voltage>...

  • Page 72: Extender Board Connections

    The Model 7700 being calibrated should be connected to the 7797 Calibration/Extender Board, and the extender board should then be installed in scanner Slot #1. Note that the module being calibrated will be external to the Model 2750 to avoid card heating during calibration.
  • Page 73 Accurately measure and record the cold temperature of the Model 7700 card sur- face at the center of the card. Press in and hold the Model 2750 OPEN key while turning on the power. Enable calibration by sending the :CODE command. For example, the default com-...
  • Page 74 2-26 Calibration Model 2750 Multimeter/Switch System Service Manual...

  • Page 75: Routine Maintenance

    Routine Maintenance...

  • Page 76: Introduction

    The information in this section deals with routine type maintenance and includes proce- dures for setting the line voltage, replacing the Model 2750 line and front terminal AMPS fuses, and replacing the amps fuses for the Models 7700 plug-in module. Replacement of the Model 2750 non-volatile RAM battery and reading module relay card closure count is also covered.

  • Page 77: Figure 3-1 Power Module

    Window Fuse Holder Assembly CAUTION Operating the Model 2750 on the wrong line voltage may result in instru- ment damage. If configuring the instrument for a different line voltage, remove the line voltage selector from the assembly, and rotate it to the proper position. When the selector is installed into the fuse holder assembly, the correct line voltage appears inverted in the window.

  • Page 78: Replacing The Amps Fuse

    Routine Maintenance Model 2750 Multimeter/Switch System Service Manual Replacing the AMPS fuse The front panel AMPS fuse protects the Model 2750 AMPS current input from an over- current condition. Follow the steps below to replace the AMPS fuse. WARNING Make sure the instrument is disconnected from the power line and other equipment before replacing the AMPS fuse.

  • Page 79: Replacing Model 7700 Plug-In Module Amps Fuses

    Model 2750 Multimeter/Switch System Service Manual Routine Maintenance Replacing Model 7700 plug-in module amps fuses WARNING The information in this section is intended only for qualified service per- sonnel. Do not perform these procedures unless you are qualified to do so.

  • Page 80: Replacing Non-Volatile Ram Battery

    Reinstall the circuit board into the plastic housing, then close the top cover. Replacing non-volatile RAM battery The Model 2750 has a three-year lithium battery for non-volatile RAM. Use the procedure below to replace the battery, if required. Refer to the disassembly procedures in...

  • Page 81: Replace The Battery As Follows

    Locate battery BT100 using the motherboard component layout drawing at the end Section De-solder the battery from the top side of the circuit board. Install a new battery, Keithley part number BA-51, taking care to observe proper polarity. Solder the battery connection to the circuit board using organic (OA-based) flux solder.

  • Page 82: Plug-In Module Relay Closure Count

    Model 2750 Multimeter/Switch System Service Manual Plug-in module relay closure count The Model 2750 keeps an internal count of the number of times each module relay has been closed. This count will help you determine if and when any relays require replace- ment (see module contact life specifications).

  • Page 83: Resetting Relay Closure Count

    Resetting relay closure count NOTE The Model 2750 must be in the manufacturing calibration mode to reset the clo- sure count. To do so, press and hold the OPEN key while turning on the power, then send the :CAL:PROT:CODE “code” to unlock calibration (default code: KI002750).

  • Page 84: Rack Mounting

    Rack mount procedure The Model 2750 can be mounted in a standard 19-inch rack. For a mainframe that has one or no switching modules installed, the Model 2750 can be secured to the front rails of the rack.

  • Page 85: Figure 3-4 Rack Preparation

    Simply pull off the rubber feet to gain access to the screws. Retain these foot assemblies for future use. Position the Model 2750 in the rack and loosely attach the front panel to the rack rails using the four supplied dress screws.
  • Page 86 3-12 Routine Maintenance Model 2750 Multimeter/Switch System Service Manual...

  • Page 87: Troubleshooting

    Troubleshooting...

  • Page 88: Introduction

    To avoid a possible shock hazard, connect the metal shield to chassis ground before servicing. Repair considerations Before making any repairs to the Model 2750, be sure to read the following considerations. CAUTION The PC boards are built using surface mount techniques and require spe- cialized equipment and skills for repair.

  • Page 89: Power-On Self-Test

    Troubleshooting Power-on self-test During the power-on sequence, the Model 2750 will perform a checksum test on its EPROM (U156 and U157) and test its RAM (U151, U152, U164 and U193). If one of these tests fails, the instrument will lock up.

  • Page 90: Principles Of Operation

    Troubleshooting Model 2750 Multimeter/Switch System Service Manual Principles of operation The following information is provided to support the troubleshooting tests and procedures covered in this section of the manual. Refer to the following block diagrams: Figure 4-1 — Power supply block diagram.

  • Page 91: Table 4-1 Power Supply Components

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting AC power is applied to the AC power module receptacle. Power is routed through the line fuse and line voltage selection switch of the power module to the power transformer. The power transformer has a total of four secondary windings for the various supplies.

  • Page 92: Display Board

    Troubleshooting Model 2750 Multimeter/Switch System Service Manual Display board Display board components are shown in the digital circuitry block diagram in Figure 4-2. Figure 4-2 Digital circuitry block diagram Battery Y103 BT100 Back Control/ Realtime Clock U171 NVRAM U151, U152...

  • Page 93: Digital Circuitry

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting Microcontroller U401 is the display board microcontroller that controls the display and interprets key data. The microcontroller uses three internal peripheral I/O ports for the various control and read functions. Display data is serially transmitted to the microcontroller from the digital section via the TXB line to the microcontroller RDI terminal.
  • Page 94 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Memory circuits ROMs U156 and U157 store the firmware code for instrument operation. U157 stores the D0-D7 bits of each data word, and U156 stores the D8-D15 bits. RAMs U151, U152, U164, and U193 provide battery backed operating storage.

  • Page 95: Analog Circuitry

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting Analog circuitry Refer to Figure 4-3 for the following discussion on analog circuitry.
  • Page 96 4-10 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Figure 4-3 Analog circuitry block diagram A/D MUX Overload Digital Protection Circuitry Q103, 107, 117, U165 (See Figure 4-2) CR101, 113, Front Terminals U128,140, 143 VR110, 111 S101 AMPS Scanner Outputs Current...
  • Page 97 Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-11 INPUT HI INPUT HI protection is provided by the SSP (Solid State Protection) circuit. The SSP is primarily made up of Q101 and Q102. An overload condition opens Q101 and Q102, which disconnects the analog input signal from the rest of the analog circuit.
  • Page 98 4-12 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Multiplexer and A/D converter All input signals, except FREQ, are routed to the A/D MUX & Gain circuit. The multi- plexer (U163) switches the various signals for measurement. In addition to the input sig- nal, the multiplexer also switches among reference and zero signals at various phases of the measurement cycle.
  • Page 99 Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-13 Figure 4-4 Simplified schematic of dry circuit ohms 20mV Reference (Main Clamp, Monitors SENSE HI) I Source 10μA 100μA 10mA 50mV Reference (Secondary Clamp, Monitors INPUT HI) ↔ SSP* SSP* 1MΩ SSP*...

  • Page 100: Troubleshooting

    4-14 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Troubleshooting Troubleshooting information for the various circuits is summarized below. See “Principles operation” for circuit theory. Display board checks If the front panel DISP test indicates that there is a problem on the display board, use Table 4-2.

  • Page 101: Digital Circuitry Checks

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-15 Digital circuitry checks Digital circuit problems can be checked using Table 4-4. Table 4-4 Digital circuitry checks Step Item/Component Required Condition Remarks Power-on test RAM OK, ROM OK. Verify that RAM and ROM are functional.

  • Page 102: Analog Signal Switching States

    4-16 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Analog signal switching states Table 4-5 through Table 4-13 provide switching states of the various relays, FETs, and analog switches for the basic measurement functions and ranges. These tables can be used to assist in tracing an analog signal from the input to the A/D multiplexer.

  • Page 103: Table 4-6 Acv And Freq Signal Switching

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-17 Table 4-6 ACV and FREQ signal switching U103 U103 Range Q101 Q102 K101* K102* Pin 8 Pin 9 100mV RESET RESET RESET RESET RESET 100V RESET 750V RESET U105 U105 U103 U103...
  • Page 104 4-18 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Table 4-7 2 signal switching Range Q101 Q102 Q151 Q150 Q122 Q135 Q114 Q136 10 100 1k 10k 100k 1M 10M 100M Range Q109 K101* K102* Q113 Q104 Q108 Q106 Q148 10...

  • Page 105: Table 4-7 2 Signal Switching

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-19 Table 4-8 4 signal switching Range Q101 Q102 Q151 Q150 Q122 Q135 Q114 Q136 1 10 100 1k 10k 100k 1M 10M 100M Range Q109 K101* K102* Q113 Q104 Q108 Q106 Q148 1...
  • Page 106 4-20 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Table 4-9 4 dry circuit signal switching Range Q101 Q102 Q151 Q150 Q122 Q135 Q114 Q136 1 10 100 1k Range Q109 K101* K102* Q113 Q104 Q108 Q106 Q148 1 RESET 10...

  • Page 107: Table 4-13 Aca Signal Switching

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-21 Table 4-11 4 dry circuit reference signal switching Range Q159 Q158 Q157 U133/0.7V U133/7V Q123 Q125 1 10 100 1k Range Q124 Q126 K104* U133/9 Q171 U208/9 U208/16 1 10 100 1k...

  • Page 108: Table 4-14 Dcv Signal Multiplexing And Gain

    4-22 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Table 4-14 through Table 4-19 can be used to trace the analog signal through the A/D mul- tiplexer (U163) to the final amplifier stage. These tables show the MUX lines (S3, S4, S6, S7) that are selected for measurement during the SIGNAL phase of the multiplexing cycle.

  • Page 109: Table 4-17 2 Signal Multiplexing And Gain

    Model 2750 Multimeter/Switch System Service Manual Troubleshooting 4-23 Table 4-17 2 signal multiplexing and gain Signal U129 U129 U129 Gain Range (U163) Pin 1 Pin 8 Pin 9 (U166) 100 10 100 100 10 1k 10 10k 10 100k 1 1M...

  • Page 110: No Comm Link Error

    4-24 Troubleshooting Model 2750 Multimeter/Switch System Service Manual Figure 4-2 provides a block diagram of the analog circuitry. Table 4-20 shows where the various switching devices are located in the block diagram. Table 4-20 Switching device locations Switching Devices Analog Circuit Section...

  • Page 111: Disassembly

    Disassembly...

  • Page 112: Introduction

    Disassembly Model 2750 Multimeter/Switch System Service Manual Introduction This section explains how to handle, clean, and disassemble the Model 2750. Disassembly drawings are located at the end of this section. Handling and cleaning To avoid contaminating PC board traces with body oil or other foreign matter, avoid touching the PC board traces while you are repairing the instrument.

  • Page 113: Static Sensitive Devices

    Use the following assembly drawings to assist you as you disassemble and reassemble the Model 2750. Refer to these drawings for information about the Keithley part numbers of most mechanical parts in the unit. The drawings are located at the end of this section of the manual.

  • Page 114: Disassembly Procedures

    Disassembly Model 2750 Multimeter/Switch System Service Manual Disassembly procedures Case cover removal Follow the steps below to remove the case cover to gain access to internal parts. WARNING Before removing the case cover, disconnect the line cord and any test leads from the instrument.

  • Page 115: Card Cage Removal

    Model 2750 Multimeter/Switch System Service Manual Disassembly Card cage removal After the motherboard has been removed, the 2-slot card cage underneath that holds plug- in modules can be removed simply by removing the three screws (two top, one bottom) that attach the card cage to the case bottom. The 3-slot card cage can be removed in a sim- ilar manner by removing the three screws (two top, one bottom) that secure it to the chas- sis, although it is not necessary to remove the motherboard to do so.

  • Page 116: Instrument Reassembly

    Disassembly Model 2750 Multimeter/Switch System Service Manual Power module removal Perform the following steps to remove the power module: Disconnect the wires going to the power transformer. Remove the POWER switch rod. Disconnect the power module’s ground wire. This green and yellow wire connects to a threaded stud on the chassis with a kep nut.

  • Page 117: Power Module Wire Connections

    Model 2750 Multimeter/Switch System Service Manual Disassembly Power module wire connections Use the information in Table 5-2 and DETAIL B of drawing 2750-050 to connect power module wires. Table 5-2 Power module wire colors Location Wire Color Top wire Gray...
  • Page 118 Disassembly Model 2750 Multimeter/Switch System Service Manual...

  • Page 119: Replaceable Parts

    Replaceable Parts...

  • Page 120: Introduction

    7700 module, refer to the modules manual. Parts lists Both electrical and mechanical parts for the Model 2750 are listed in several tables on the following pages. For additional information on mechanical parts, see the assembly draw- ings provided at the end of...

  • Page 121: Component Layouts

    Model 2750 Multimeter/Switch System Service Manual Replaceable Parts Component layouts Component layouts for the various circuit boards are provided on the following pages. Table 6-1 Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. BT100 L1 BATTERY, 3.6V, 950MAH...
  • Page 122 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. C171,C177 CAP, 2200P, 10%, 100V, CERAMIC C-430-2200P C175,C209 CAP, 22UF, 20%, 25V, TANTALUM C-440-22 C179,C266 CAP, 100PF, 5%, 100V, CERAMIC...
  • Page 123 Model 2750 Multimeter/Switch System Service Manual Replaceable Parts Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. J1008 LATCHING HEADER, FRICTON, CS-724-3 SGL ROW J1010 CONN, FEMALE, 8 PIN CS-612-8 J1012 CONN, HEADER STRAIGHT SOLDER PIN CS-368-20...
  • Page 124 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. R104,R105 RES, 549K, .1%, 1/4W, METAL FILM R-315-549K R106 RES, 11K, .1%, 1/10W, METAL FILM R-263-11K R107 RES, 49.9, 1%, 1/4W, METAL FILM R-391-49.9...
  • Page 125 Model 2750 Multimeter/Switch System Service Manual Replaceable Parts Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. R157,R243 RES, 499, 1%, 100MW, THICK FILM R-418-499 R158 RES, .1, 1%, 2W, 4-TERMINAL MOLDED R-342-.1 R159,R360,R168,R182,R239,R247, RES, 1K, 1%, 1/4W, METAL FILM...
  • Page 126 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. R251,R256,R263,R284,R288, RES, 1K, 1%, 100MW, THICK FILM R-418-1K R298,R340 R259,R320 RES, 10, 10%, 100MW, THICK FILM R-418-10 R262...
  • Page 127 Model 2750 Multimeter/Switch System Service Manual Replaceable Parts Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. R369 RES, 10M, 1%, 125MW, THICK FILM R-418-10M R386 RES NET 50K, 1%, .5W, THICK FILM TF-243-50K R387...
  • Page 128 6-10 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. U125 IC, +15V VOLTAGE REGULATOR IC-1241 U127,U173,U174,U181,U196 IC, QUAD 2 IN AND, 74HCT08 IC-837 U128,U166 IC, OP-AMP, MC34081BD...
  • Page 129 Model 2750 Multimeter/Switch System Service Manual Replaceable Parts 6-11 Table 6-1 (continued) Model 2750 motherboard parts list Circuit Designation Description Keithley Part No. U192 IC, 2 - INPUT AND GATE IC-1140 U194 IC, CONTROLLER WITH MONITOR IC-1424 U195 IC, 3 TO 8 LINE DECODER...
  • Page 130 6-12 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-2 Model 2750 display board parts list Circuit Designation Description Keithley Part No. C401-C405,C407,C409-C412 CAP, .1UF, 20%, 50V, CERAMIC C-418-.1 C406,C408 CAP, 33PF, 10%, 100V, CERAMIC C-451-33P C413 CAP, 22UF, 20%, 6.3 TANTALUM...
  • Page 131 Model 2750 Multimeter/Switch System Service Manual Replaceable Parts 6-13 Table 6-3 Model 2750 backplane board parts list Circuit Designation Description Keithley Part No. J1,J2 CONN 2 ROWS OF 16 PINS CS-736-4 J1,J2,J3 CONN 2 ROWS OF 16 PINS CS-736-4 CONN, RT ANGLE, HEADER...
  • Page 132 6-14 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-4 Model 2750 miscellaneous parts list Qty. Description Keithley Part No. 3 SLOT CARD CAGE 2750-316B 5X20MM SNAP-IN FUSE HOLDER FH-40 BANANA JACK, PUSH-IN, BLACK BJ-14-0 BANANA JACK, PUSH-IN, RED...

  • Page 133: Table 6-5 Model 7700 Module Parts List

    Model 2750 Multimeter/Switch System Service Manual Replaceable Parts 6-15 Table 6-5 Model 7700 module parts list Circuit Designation Description Keithley Part No. C1,C9,C10,C11,C14,C15,C22,C4 CAP, 0.1UF, 20%, 50V, CERAMIC C-418-.1 CAP, 220U, 20%, 10V, TANTALUM C-558-220 C17,C18,C19,C21,C25,C26,C23, CAP, 47P, 5%, 100V, CERAMIC...
  • Page 134 6-16 Replaceable Parts Model 2750 Multimeter/Switch System Service Manual Table 6-5 (continued) Model 7700 module parts list Circuit Designation Description Keithley Part No. R60,R61 RES, 4.22K, 1%, 125MW, METAL FILM R-391-4.22K R62,R63 RES, 137, 1%, 125MW, METAL FILM R-391-137 R64,R65,R66,R67,R68,R69,R70,...

  • Page 135: Accuracy And Optimization

    Accuracy and Optimization...

  • Page 136: Accuracy Calculations

    Accuracy and Optimization Model 2750 Multimeter/Switch System Service Manual Accuracy calculations The information below discusses how to calculate accuracy for both DC and AC characteristics. Calculating DC characteristics accuracy DC characteristics accuracy is calculated as follows: Accuracy = ±(ppm of reading + ppm of range) (ppm = parts per million, and 10ppm = 0.001%)

  • Page 137: Calculating Dbm Characteristics Accuracy

    Model 2750 Multimeter/Switch System Service Manual Accuracy and Optimization Calculating dBm characteristics accuracy As an example of how to calculate the actual reading limits for a 13dBm measurement with a reference impedance of 50, assume an applied signal 0.998815V. The relationship between voltage and dBm is as follows: ...

  • Page 138: Additional Derating Factors

    Accuracy and Optimization Model 2750 Multimeter/Switch System Service Manual Thus, the actual reading accuracy is 10mV ±36mV or 10.036mV to 9.964mV. Applying the voltage reading accuracy into the dB equation yields: 10.036mV – 59.96879dB ------------------------- - 9.964mV – 60.03133dB ---------------------- - Thus, the actual reading accuracy is -60dB + 0.031213dB to -60dB - 0.031326dB.

  • Page 139: Optimizing Measurement Speed

    Model 2750 Multimeter/Switch System Service Manual Accuracy and Optimization Optimizing measurement speed The configurations listed below assume that the multimeter has had factory setups restored. DC voltage, DC current, and resistance: • Select 3-1/2 digits, 0.01 PLC, filter OFF, fixed range.
  • Page 140 Accuracy and Optimization Model 2750 Multimeter/Switch System Service Manual...

  • Page 141: Calibration Reference

    Calibration Reference...

  • Page 142: Introduction

    Calibration Reference Model 2750 Multimeter/Switch System Service Manual Introduction This appendix contains detailed information about the various Model 2750 remote calibra- tion commands. Section 2 of this manual covers detailed calibration procedures. For infor- mation about additional commands to control other instrument functions, refer to the Model 2750 User’s Manual.
  • Page 143 Model 2750 Multimeter/Switch System Service Manual Calibration Reference Table B-1 (continued) Remote calibration command summary Command Description :CALibration :PROTected :STEP10 <NRf> 10mA DC step. :STEP11 <NRf> 100mA DC step. :STEP12 <NRf> 1A DC step. AC cal steps. :STEP1 10mV AC at 1kHz step.

  • Page 144: Miscellaneous Calibration Commands

    The code parameter must be enclosed in single quotes. Example :CAL:PROT:CODE 'KI002750' Send default code of KI002750. :COUNt? (:CALibration:PROTected:COUNt?) Purpose To determine how many times the Model 2750 has been calibrated. Format :cal:prot:coun? Response <n> Calibration count. Description The :COUNt? command allows you to determine how many times the Model 2750 has been calibrated.
  • Page 145 :cal:prot:init Parameters None Description The :INIT command enables Model 2750 calibration when perform- ing these procedures over the bus. This command must be sent to the unit after sending the :CODE command, but before sending any other calibration command. NOTE...
  • Page 146 :cal:prot:lock? Response Comprehensive calibration locked. Comprehensive calibration unlocked. Description The :LOCK? query requests status from the Model 2750 on calibration locked/unlocked state. Calibration must be enabled sending the :CODE command before calibration can be performed. Example Request cal lock state.
  • Page 147 Model 2750 Multimeter/Switch System Service Manual Calibration Reference :DATE (:CALibration:PROTected:DATE) Purpose To send the calibration date to the instrument. Format :cal:prot:date <year>, <month>, <day> Parameters <year> = 2000 to 2099 <month> = 1 to 12 <day> = 1 to 31...

  • Page 148: Dc Calibration Commands

    Calibration Reference Model 2750 Multimeter/Switch System Service Manual DC calibration commands The :DC commands perform calibration of the DCV, DCI, and ohms functions. Table B-2 summarizes these calibration commands along with parameter limits. Table B-2 DC calibration commands Command Description...
  • Page 149 Model 2750 Multimeter/Switch System Service Manual Calibration Reference :STEP2 (:CALibration:PROTected:DC:STEP2) Purpose To perform front terminal open-circuit calibration. Format :cal:prot:dc:step2 Parameters None Description :STEP2 performs the open-circuit calibration step in the comprehen- sive calibration procedure. Disconnect all cables and accessories from the input jacks before sending this command.
  • Page 150 B-10 Calibration Reference Model 2750 Multimeter/Switch System Service Manual :STEP5 (:CALibration:PROTected:DC:STEP5) Purpose To program the 100V DC comprehensive calibration step. Format :cal:prot:dc:step5 <Cal_voltage> Parameters <Cal_voltage> = 90 to 110 [V] Description :STEP5 programs the 100V DC comprehensive calibration step. The allowable range of the calibration voltage parameter is from 90 to 110, but 100 is recommended for best results.
  • Page 151 Model 2750 Multimeter/Switch System Service Manual Calibration Reference B-11 :STEP8 (:CALibration:PROTected:DC:STEP8) Purpose To program the 100k 4-wire comprehensive calibration step. Format :cal:prot:dc:step8 <Cal_resistance> Parameters <Cal_resistance> = 90E3 to 110E3 [] Description :STEP8 programs the 100k 4-wire resistance comprehensive calibra- tion step. The allowable range of the calibration resistance parameter is from 90E3 to 110E3, but 100E3 is recommended for best results.
  • Page 152 B-12 Calibration Reference Model 2750 Multimeter/Switch System Service Manual :STEP11 (CALibration:PROTected:DC:STEP11) Purpose To program the 100mA comprehensive calibration step. Format :cal:prot:dc:step11 <Cal_current> Parameters <Cal_current> = 90E-3 to 110E-3 [A] Description :STEP11 programs the 100mA comprehensive calibration step. The allowable range of the calibration current parameter is from 90E-3 to 110E-3.

  • Page 153: Ac Calibration Commands

    Model 2750 Multimeter/Switch System Service Manual Calibration Reference B-13 AC calibration commands The :AC commands perform comprehensive (user) calibration of the ACV and ACI func- tions. Table B-3 summarizes these calibration commands. Table B-3 AC calibration commands Command Description :CALibration...
  • Page 154 B-14 Calibration Reference Model 2750 Multimeter/Switch System Service Manual :AC:STEP<n> (CALibration:PROTected:AC:STEP<n>) Purpose To program individual AC calibration steps. Format :cal:prot:ac:step<n> Parameters 10mV AC at 1kHz calibration step. 100mV AC at 1kHZ calibration step. 100mV AC at 50kHz calibration step. 1V AC at 1kHz calibration step.

  • Page 155: Manufacturing Calibration Commands

    Model 2750 Multimeter/Switch System Service Manual Calibration Reference B-15 Manufacturing calibration commands NOTE To perform these steps, manufacturing calibration must be enabled by pressing and holding the OPEN key while turning on the power. See Section Three calibration steps are only performed at the factory or when the unit has been...

  • Page 156: Model 7700 Calibration Commands

    B-16 Calibration Reference Model 2750 Multimeter/Switch System Service Manual Model 7700 calibration commands Table B-4 summarizes calibration commands for the Model 7700 plug-in module. Note that CARD1 commands calibrate the card in Slot 1, while CARD commands request cali- bration count, date, and reference temperature information from a card in Slot 1 through Slot 5.
  • Page 157 Up to an 8-character string including letters and numbers. Description The :CODE command enables the Model 2750 calibration procedures when performing these procedures over the bus. This command must be sent to the unit before sending any other Model 7700 calibration com- mand.
  • Page 158 Model 7700 in Slot 1 through Slot 5 respectively (<NRf> = 1 to 5). NOTE The card calibration date is automatically set to the Model 2750 real time clock date when the card is calibrated. Example Request card 1 cal date.
  • Page 159 Response Calibration locked. Calibration unlocked. Description The :LOCK? query requests status from the Model 2750 on Model 7700 calibration locked/unlocked state. Calibration must be enabled sending the :CODE command before calibration can be performed. Example Request card 1 cal lock state.
  • Page 160 B-20 Calibration Reference Model 2750 Multimeter/Switch System Service Manual :SAVE (:CALibration:PROTected:CARD1:SAVE) Purpose To save calibration constants in card EEROM after the calibration pro- cedure. Format :cal:prot:card1:save Parameters None Description The :SAVE command stores calculated calibration constants derived during Model 7700 calibration in card EEROM. (EEROM is non- volatile memory.) Calibration constants will be retained indefinitely...

  • Page 161: Remote Error Reporting

    Model 2750 calibration errors, including error numbers and error messages. NOTE Error numbers and error messages are separated by commas. All calibration errors will set Bit 3 in the Standard Event Register. See the Model 2750 User’s Manual. Table B-5 Calibration errors...
  • Page 162 B-22 Calibration Reference Model 2750 Multimeter/Switch System Service Manual Table B-5 (continued) Calibration errors Error Number Error Message +417 “10k 4-w full scale error” +418 “100k 4-w full scale error” +419 “1M 4-w full scale error” +420 “10M 4-w full scale error”...
  • Page 163 Model 2750 Multimeter/Switch System Service Manual Calibration Reference B-23 Table B-5 (continued) Calibration errors Error Number Error Message +461 “10 vac noise error” +462 “100 vac zero error” +463 “100 vac full scale error” +464 “750 vac zero error” +465 “750 vac full scale error”...

  • Page 164: Error Queue

    *Model 7700 card only. Error queue As with other Model 2750 errors, any calibration error will be reported in the bus error queue. You can read this queue by using the :SYST:ERR? query. The Model 2750 will respond with the appropriate error number and message, as summarized in Table B-5.

  • Page 165: Status Byte Eav (Error Available) Bit

    Model 2750 Multimeter/Switch System Service Manual Calibration Reference B-25 Status byte EAV (Error Available) bit Whenever an error is available in the error queue, the EAV (Error Available) bit (bit 2) of the status byte will be set. Use the *STB? query or serial polling to obtain the status byte, then test bit 2 to see if it is set.

  • Page 166: Using The *Opc Command

    An IEEE-488 bus SRQ (service request) can be used to detect operation complete instead of repeatedly polling the Model 2750. To use this method, send both *ESE 1 and *SRE 32 to the instrument, then include the *OPC command at the end of each calibration com- mand line, as covered above.

  • Page 167: Calibration Program

    Calibration Program...

  • Page 168: Introduction

    The following computer hardware is required to run the calibration program: • IBM PC, AT, or compatible computer. • Keithley KPC-488.2, KPS-488.2, or KPC-488.2AT, or CEC PC-488 IEEE-488 interface for the computer. • Two shielded IEEE-488 connecting cables (Keithley Model 7007).

  • Page 169: General Program Instructions

    Turn on the computer, Model 2750, and calibrator. Allow the Model 2750 and the calibrator to warm up for at least one hour before performing calibration. Make sure the Model 2750 is set for a primary address of 16. (Use the front panel GPIB key to check or change the address.) Make sure the calibrator primary address is at its factory default setting of 4.
  • Page 170 PRINT #1, "OUTPUT 4;"; Msg$ PRINT #1, "OUTPUT 4;OPER" END SELECT IF I > 2 THEN GOSUB Settle PRINT #1, "OUTPUT 16;"; C$; Cmd$; ";*OPC" ' Send cal command to 2750. GOSUB CalEnd ' Wait until cal step ends. GOSUB ErrCheck ' Check for cal error.
  • Page 171 Model 2750 Multimeter/Switch System Service Manual Calibration Program DO: I$ = INKEY$: LOOP WHILE I$ = "" IF I$ = CHR$(27) THEN GOTO EndProg ' Abort if ESC is pressed. RETURN CalEnd: ' Check for cal step completion. PRINT "Performing calibration step #"; I DO: PRINT #1, "SRQ?"...
  • Page 172 Calibration Program Model 2750 Multimeter/Switch System Service Manual DATA "OUT 1 V,1 KHZ","AC:STEP4" DATA "OUT 1 V,50 KHZ","AC:STEP5" DATA "OUT 10 V,1 KHZ","AC:STEP6" DATA "OUT 10 V,50 KHZ","AC:STEP7" DATA "OUT 100 V,1 KHZ","AC:STEP8" DATA "OUT 100 V,50 KHZ","AC:STEP9" DATA "OUT 700 V,1 KHZ","AC:STEP10"...
  • Page 173 Index block diagram 4-10 Analog signal switching states 4-16 Assembly drawings STEP B-14, B-15 battery CODE B-4, B-17 replacement COUNt? B-4, B-17 DATE DATE? B-18, B-19 Calibration calibration STEP0 B-15 aborting INIT B-5, B-18 AC current 2-13 LOCK B-5, B-18 AC voltage 2-12 LOCK?
  • Page 174 Connections Digital I/O AC volts calibration 2-12 Disassembly DC and AC amps calibration 2-11 Disassembly procedures DC volts and ohms calibration DISP test Input terminal wire Display manufacturing calibration 2-22 Display board Model 2700 AC current verification 1-13 Display board checks 4-14 Model 2700 AC volts verification 1-10...
  • Page 175 Disassembly Performance Verification No comm link error 4-24 Replaceable Parts Routine Maintenance troubleshooting operation principles Ordering information Key matrix KEY test Parts lists Performance Verification limits power components ACI, Model 2700 1-13 removing DCI, Model 2700 1-12 Power module removal Plug-in module ACI, Model 7700 1-26 Power module wire colors...
  • Page 176 Programming calibration dates 2-19 resistance 2-16 W2 signal multiplexing and gain 4-23 Saving calibration constants 2-19 W2 signal switching 4-18 short and open 2-15 W2/W4 reference switching 4-20, 4-21 Remote error reporting B-21 W4 signal multiplexing and gain 4-23 Repair considerations W4 signal switching 4-19, 4-20 Replaceable Parts...
  • Page 177 Service Form Model No. _______________ Serial No. __________________ Date _________________ Name and Telephone No. ___________________________________________________ Company _______________________________________________________________________ List all control settings, describe problem and check boxes that apply to problem. _________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ ❑ Intermittent ❑ Analog output follows display ❑...

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