Summary of Contents for A & A Scales PT300
- Page 1 PT300 Service Manual A & A Scales 1-813-994-3190 Fax 509-355-3498 www.stainlessscales.com...
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Page 2: Rev B, October
PT300, Service Manual Rev B, October, 2000 SAFETY SUMMARY The following general safety precautions must be observed during all phases of operation, service, and repair of this scale. Failure to comply with these precautions or with specific warnings elsewhere in this manual violates safety standards of design, manufacture, and intended use of the scale. -
Page 3: Table Of Contents
PT300, Service Manual Rev B, October, 2000 Table of Contents SCOPE OF MANUAL ............................5 SPECIFICATIONS.............................. 6 ............................... 6 LECTRICAL :........................6 ERIAL INTERFACE SPECIFICATIONS ................................6 HYSICAL ............................... 7 NVIRONMENTAL :..............................7 ALIBRATION THEORY OF OPERATION ..........................9 :..............................9 OWER SUPPLY Input protection:............................ - Page 4 OMPLETE LIST OF REQUIRED TOOLS AND MATERIALS Spare parts list ............................34 Connector pinouts ............................36 ..........................36 RANSMIT ATA FORMAT PT300 M ..........................37 IRCUIT OARD ...............................37 ARTS PT300 SUMMING CIRCUIT BOARD PARTS LIST ..................39 APPENDIX A..............................40 APPENDIX B..............................44 ..............................44 CHEMATICS ............................47 OTALIZING CABLE .............................48 HARGING ABLE ..........................50 NTERNAL...
- Page 5 PT300, Service Manual Rev B, October, 2000 Table of Illustrations ....................8 IGURE LOCK IAGRAM .................... 9 IGURE ATTERY HARGER ......................10 IGURE WITCH ................12 IGURE NTEGRATOR OMPARITOR ..................13 IGURE ONVERSION YCLE 6 LCD D ...................... 15 IGURE...
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Page 6: Scope Of Manual
Caution Your PT300 scale is covered by a one year warranty and should be referred to the factory for maintenance within the warranty period. Attempts to make any extensive repairs within the warranty period may invalidate the warranty. If repairs are needed after the warranty period, only qualified technicians should attempt such repairs. -
Page 7: Specifications
PT300, Service Manual Rev B, October, 2000 Specifications Electrical Display settling 950 milliseconds to typical reading (static). time: Accuracy: ±1% of applied load ±1 display division in static mode ±2% of applied load ±1 display division in roll-over mode. Overcapacity: 105% of nominal capacity. -
Page 8: Environmental
10 to 95% Non-Condensing. Calibration: All scales are calibrated at the factory, a fine span adjustment can be made using the potentiometer on the PT300 circuit board. This scale can be used while it is charging. Caution Operation outside the range of -20°F to 150°F (-28°C to 65°C) may result in inaccurate weight values. -
Page 9: Figure 1 Block Diagram
PT300, Service Manual Rev B, October, 2000 Power Supply Battery Low Battery Sensor On Off Lamp Lb/Kg Zero Hold/Rel Input Micro Drivers Total/Local Buffer Controller Print Switches Display Connector Connector Serial Serial Input Output Input Output Receiver Loadcells Summing Board... -
Page 10: Theory Of Operation
PT300, Service Manual Rev B, October, 2000 Theory of Operation For the following discussion, please refer to the schematics in appendix B. Power supply: The power supply section provides a source of ±5 volts, a nickel-cadmium battery charger, and the detector for low battery condition. The input is designed to accept any voltage between 10.5 and 14.6 volts. -
Page 11: Charger
PT300, Service Manual Rev B, October, 2000 Charger: The battery charger works on the constant voltage charging principle. The diode D4 is a 10 volt zener diode. This diode is biased by the constant current source formed by R1, R2, Q8, D2, and D3. Current is sourced to D4 until the voltage across R2 is equal to the voltage dropped across D2. -
Page 12: Low Voltage Sensor
PT300, Service Manual Rev B, October, 2000 Low Voltage Sensor: R9, D7, and Q2 work much the same as R6, D6 and Q5 in the power switch section. The addition of D8 causes Q2 to switch 0.3 volts before Q5. In practical terms, Q2 will be biased on until the switched voltage drops to 7.2 volts. -
Page 13: Analog Section
PT300, Service Manual Rev B, October, 2000 Analog Section: The analog section takes the signal from the load cells (about 10 mV) and translates this signal into a digital representation. In our case this representation is a sixteen bit number in a counter register. -
Page 14: Figure 5 Conversion Cycle
PT300, Service Manual Rev B, October, 2000 Integrate Deintegrate U17 Pin 1 Auto Zero Auto Zero Figure 5 Conversion Cycle Let’ s examine the operation of the converter. Start with C7 at zero volts. The +input voltage charges C7 for a fixed period called Time-integrate. Then the integrator input is switched to the reference voltage and C7 is discharged for an amount of time called Time-deintegrate;... -
Page 15: Microprocessor Section
PT300, Service Manual Rev B, October, 2000 Now for the messy details of implementation; U17 is driven through the integrate, deintegrate, and auto-zero cycles by a counter U12. This counter is loaded by the micro processor to start the cycle, and U12 pin 6 output is used as an interrupt to signal that the conversion is over. -
Page 16: Display Driver
PT300, Service Manual Rev B, October, 2000 Display Driver: Any LCD display must be driven by a waveform with a net zero DC voltage. If the driving voltage has any DC component the display will be destroyed. A display driver chip (U10) provides the correct drive for 4 of the display digits. -
Page 17: Troubleshooting
PT300, Service Manual Rev B, October, 2000 Troubleshooting Caution Changing some parts may cause a large change in calibration whereas others may or may not change the calibration, depending on the nature of the problem. The most sensitive parts are in the analog and power supply sections; this includes Q3, U17, U18, U19, and their related resistors and capacitors. -
Page 18: Scale Shuts Off
PT300, Service Manual Rev B, October, 2000 Scale shuts off. Normally the scale shuts itself off after a long period of inactivity. The length of time is defined at the time the scale is configured, but is normally one hour. If the microprocessor is acting up, one of the symptoms may be that the scale shuts off after the A/D is initialized and starts to run. -
Page 19: Low Batt Indicator Won't Turn Off
PT300, Service Manual Rev B, October, 2000 Low batt indicator won't turn off. It is possible that the output from the batteries is really low. Look at the cells and charger circuit for these problems. The low voltage sensor could be out. -
Page 20: Tests, Waveforms And
PT300, Service Manual Rev B, October, 2000 Tests, Waveforms and Voltage measurements Blank EPROM test. One of the most challenging problems is finding a problem in the "microprocessor kernel," that is, the RAM, ROM, microprocessor and related circuitry. The hardest part is that everything is tied together, and if you cut it apart, nothing works. -
Page 21: Figure 7 Blank Eeprom Test Waveforms
PT300, Service Manual Rev B, October, 2000 _____ RFSH 0038h RFSH See Below See Below 0FFh 039h Figure 7 Blank EEPROM Test Waveforms For the first three clock pulses the Z80 reads 0FFH from location 038H. As part of an instruction fetch the Z80 does a memory refresh cycle. We do not use this for anything, but its there. -
Page 22: Figure 8 Blank Eeprom Test, Address Lines
PT300, Service Manual Rev B, October, 2000 A15 20mS/Div A14 10mS/Div A13 5mS/Div A12 2mS/Div A11 1mS/Div A10 0.5 mS/Div A09 0.1mS/Div A08 50mS/Div A07 0.1mS/Div A06 0.1mS/Div A05 0.1mS/Div A04 50mS/Div A03 20mS/Div A02 10mS/Div A01 5mS/Div A00 2mS/Div... -
Page 23: System Checkout Procedure
PT300, Service Manual Rev B, October, 2000 System checkout procedure The following measurements are typical values. When tolerances are given the signal must fall within the given ranges. Special measuring conditions will be specified as needed. The measurements are given in the order that you should use them. -
Page 24: Amplifier
PT300, Service Manual Rev B, October, 2000 If the display backplane drive is missing, TURN THE SCALE OFF IMMEDIATELY. Operation without a backplane signal will damage the display quickly. Remove the display while determining the cause of the missing backplane signal. Display damage will be evident as display segments that are on permanently, even with the scale off. -
Page 25: Sio (Totalizing)
PT300, Service Manual Rev B, October, 2000 SIO (totalizing): To test the totalizing function you will need 2 scales (one is the scale under test) and a totalizing cable. Put the scale under test into the master position, and the other scale in the second position on the cable. - Page 26 PT300, Service Manual Rev B, October, 2000 Turn both scales off. Now put the scale under test in the slave position and the other scale in the master position, like this . . . Scale under test Master Leave any other cable...
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Page 27: Load Cells
Rev B, October, 2000 Load Cells: Each PT300 scale has two load cells. These load cells are the transducers that convert mechanical energy (weight) to electrical energy. Each load cell has 4 strain gages (1000 ohms each) and a temperature compensation resistor. The four strain gages are wired together to form a Wheatstone bridge. -
Page 28: Procedures
At several points in the following procedures you will be asked to use loading blocks. The tip of a test press may exert 20000 pounds of force. While PT300 scales are designed to accept this force, they may not tolerate this on a single point. You must use a block to distribute the force over the load surface. - Page 29 PT300, Service Manual Rev B, October, 2000 11) Apply 5000, 10000, 15000, and 19000 lbs and verify span is within 1.0% of applied load. Make any adjustments necessary to bring the unit into tolerance. Insure that unit does not indicate overcapacity before 20000 lbs of applied weight.
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Page 30: Remove And Replace Main Circuit Board
PT300, Service Manual Rev B, October, 2000 Remove and replace main circuit board Tools required Twenty thousand pound calibration press. 8" x 8" x 2 ± .25” aluminum loading block. 8" x 8" x 0.5" rubber loading pad. Static dissipation station. -
Page 31: Remove And Replace Load Cell
PT300, Service Manual Rev B, October, 2000 Remove and replace load cell Tools required Twenty thousand pound calibration press. 8" x 8" x 2 ± .25” aluminum loading block. 8" x 8" x 0.5" rubber loading pad. Static dissipation station for any P.C. board work. -
Page 32: Assembly
PT300, Service Manual Rev B, October, 2000 Assembly 16) Set new load cell in place. 17) Glue the load cell lead off to the side so it doesn’ t run under the middle of the load cells. 18) Thread load cell lead through hole in case. -
Page 33: Figure 13 Load Cell Placement
PT300, Service Manual Rev B, October, 2000 Figure 13 Load Cell Placement 1) Remove all 10 bezel screws. 2) Detach keyboard assembly and set aside. Do not unplug keyboard. 3) Remove 2 screws holding circuit board. 4) Remove main circuit from housing. - Page 34 PT300, Service Manual Rev B, October, 2000 the battery tube and the printed circuit board. 17) Install tow board mounting screws. 18) Check and adjust calibration as needed. 19) Reassemble keyboard assembly 20) Replace bezel screws...
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Page 35: Unpacking And Installation
PT300, Service Manual Rev B, October, 2000 Unpacking and Installation Caution: Keep all packing materials in case scale must be shipped again. If the packing material are lost or damaged, contact the service department for a replacement shipping carton. Units shipped in any other materials will automatically void the warranty. - Page 36 PT300, Service Manual Rev B, October, 2000 Spare keypad. Main circuit board. Summing board. Load Cells. Check straps. Charging transformer. Span resistors, 124Ω , 174Ω .
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Page 37: Connector Pinouts
PT300, Service Manual Rev B, October, 2000 Connector pinouts A: +5V B: - Input C: Ground D: - Output E: +12V (Charging Voltage) F: + Input G: Unused H: + Output Transmit Data format Format = A_O_-XXXXXXX._Lb<CR><LF> Format explanation: A = Scale code (Signifies the scale, could be A for scale A, B for scale B etc..) -
Page 38: Pt300 Main Circuit Board
PT300, Service Manual Rev B, October, 2000 PT300 Main Circuit Board Parts List PT300 Circuit Board Reference: Quantity: 1.22Mhz Crystal Liquid Crystal Display (LXD # 65R9F09KGJ) LED’ s D9,D10,D11,D12, D13,D14,D15,D16 Right Angle Post Header AMP #1-640457-0 28 pin DIP Socket... - Page 39 PT300, Service Manual Rev B, October, 2000 4.7K ohm ¼ w 5% R5,R31 10K ohm ¼ w 5% R6,R9,R10,R32 10K ohm ¼ w 1% 47K ohm ¼ w 5% 100K ohm SIP, 8pin, #1 common 150K ohm ¼ w 1% R25,R26 180K ohm ¼...
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Page 40: Pt300 Summing Circuit Board Parts List
PT300, Service Manual Rev B, October, 2000 PT300 SUMMING CIRCUIT BOARD PARTS LIST PT300 Summing Board Rev. 1 Reference: Quantity: 14pin Dual Row, 90º, Header 3M #2414-5222TG 10K ohm Trim Pot R1,R2,R3,R4 47M ohm ¼ w 1% 15M ohm ¼ w 5% 22M ohm ¼... -
Page 41: Figure 14 Summing Board
PT300, Service Manual Rev B, October, 2000 Appendix A Setting the deadload. The output signal from the load cells is set to a value slightly above zero with zero weight applied. This is done for two reasons; one is to detect any errors in the load cells, the other is to run the A/D converter in its most accurate operating point. - Page 42 PT300, Service Manual Rev B, October, 2000 It is assumed that the scale is disassembled with the main circuit board removed from the case (but still plugged in) and sitting on an insulating surface. The keypad must be plugged into the main circuit board.
- Page 43 PT300, Service Manual Rev B, October, 2000 Selecting the Initial Span Range. It may be necessary to change the span resistor if you run out of travel when setting scale span. Likewise the span resistor may have to be changed when new circuit boards or load cells are installed.
- Page 44 PT300, Service Manual Rev B, October, 2000 Schematics and Parts layout Number Title Pages 072391-102 PT300 Schematic None PT300 Board Assembly None PT300 Internal harness None PT300 Summing Board None Scale Interconnect Cables 000196 PT300 Assembly...
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Page 45: Schematics
PT300, Service Manual Rev B, October, 2000 Appendix B Schematics... - Page 46 PT300, Service Manual Rev B, October, 2000...
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Page 48: Totalizing Cable
PT300, Service Manual Rev B, October, 2000 Totalizing cable... -
Page 49: Charging Cable
PT300, Service Manual Rev B, October, 2000 Charging Cable... - Page 50 PT300, Service Manual Rev B, October, 2000 Loadcell and Summing Board...
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Page 51: Internal Cable Assembly
PT300, Service Manual Rev B, October, 2000 Internal Cable Assembly... -
Page 52: Parts
PT300, Service Manual Rev B, October, 2000 Parts...