Welch Allyn Stow-A-Weigh 5202 Service Manual
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Welch Allyn Stow-A-Weigh 5202 Service Manual

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Welch Allyn Stow-A-Weigh Scales
Service Manual
Model 5202 – Stow-A-Weigh Stand-On Scale
Model 6202 – Stow-A-Weigh Wheel Chair Scale
Model 6202D – Stow-A-Weigh Wheel Chair Scale, Dual Platform

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Summary of Contents for Welch Allyn Stow-A-Weigh 5202

  • Page 1 Welch Allyn Stow-A-Weigh Scales Service Manual Model 5202 – Stow-A-Weigh Stand-On Scale Model 6202 – Stow-A-Weigh Wheel Chair Scale Model 6202D – Stow-A-Weigh Wheel Chair Scale, Dual Platform...
  • Page 2 © 2016 Welch Allyn. All rights are reserved. To support the intended use of the product described in this publication, the purchaser of the product is permitted to copy this publication, for internal distribution only, from the media provided by Welch Allyn. No other use, reproduction, or distribution of this publication, or any part of it, is permitted without written permission from Welch Allyn.

  • Page 3: Table Of Contents

    ONTENTS Scale Setup ..............................4 Enter custom setup mode ......................... 4 Set the options ............................4 power down the scale..........................6 Enter Advanced Service Mode ........................6 Menu List for Advanced Service Mode ....................6 Support services ............................7 Device Warranty ............................

  • Page 4: Scale Setup

    Scale Setup You can customize the scale to best suit your needs. Configurations that can be selected include the automatic shut-off time, weighing units, weight resolution, and more. Enter custom setup mode 1. Lower the weighing platform to the weighing position. 2.
  • Page 5 Press RE CALL to switch between ON and OFF. rECALL* Press RE CALL to change the RE CALL button functionality between ON and OFF. rS-232 Detailed instructions for this feature are available from Welch Allyn. Go to http:// www.welchallyn.com/en/other/contact-us.html to find your local representative.

  • Page 6: Power Down The Scale

    1 bit: One stop at the end of a word 2 bits: Two stops at the end of a word rtS.ctS* Press RE CALL to switch between ON for the printer and OFF for RS232 transmissions. Prtbtn* Press RE CALL to turn On or Off the front panel PRINT button. rtEPrt* Press RE CALL to turn On or Off the enabling of printing from a remote location by connecting the receive line to the ground.

  • Page 7: Support Services

    12. “CALS” = Cal mode, next display will show the number of times the unit has entered into the Cal mode. Support services If you have a problem with the device that you cannot resolve, call the Welch Allyn Technical Support Center nearest you for assistance. A representative will assist you in troubleshooting the problem and will make every effort to solve the problem over the phone, potentially avoiding an unnecessary return.

  • Page 8: Device Warranty

    Device Warranty Welch Allyn will warranty the weight scale to be free of defects in material and workmanship and to perform in accordance with manufacturer specifications for the period of one year from the date of retail purchase. The warranty period shall start on the date of purchase. The date of purchase is:...

  • Page 9: Returning Products

    If you are advised to return a product to Welch Allyn for repair or routine maintenance, schedule the repair with the service center nearest you. Returning products When returning a product to Welch Allyn for service, ensure that you have the following information: •...

  • Page 10: Scale Technical Description

    The function of the load cell transducer is to convert the weight applied to the weighing platform into an electrical signal for further processing and subsequent display by the readout. WELCH ALLYN uses proprietarily designed load cells in most of the scales to optimize performance and reliability. One of three types of load cell transducers may be used in your WELCH ALLYN scale depending on the model number.
  • Page 11 SCALE ELECTRONICS Scale electronics consist of the following: 1. Differential signal amplification. 2. Additional amplification and signal filtering. 3. Analog-to-Digital (A/D) converter and Clock circuit. 4. Battery and support circuitry, voltage regulators, power supplies, etc. 5. Microcomputer and support circuitry. 6.
  • Page 12 ANALOG-TO-DIGITAL (A/D) CONVERSION Integrated circuit U6 is the analog-to-digital converter. Included on this integrated circuit are auto-zero functions, auto-polarity, and the digital and analog functions necessary to perform dual slope integration conversion to 20,000 counts (4½ digits). The weight signal voltage is applied to the analog input (pin 10) of U6. A reference voltage for the conversion is applied to pin 2 of U6.
  • Page 13 120 KHz. POWER SWITCHING, VOLTAGE REGULATION AND SUPPORT CIRCUITRY Depending upon their configuration, WELCH ALLYN STOW-A-WEIGH® scales operate on ordinary disposable alkaline cells. Additional circuitry is included to switch the battery supply, provide voltage regulation, and detect low battery voltage conditions.
  • Page 14 Once Q1 is on and voltage is applied to the circuit, watchdog timer U11 will keep transistor Q2 on through output line /WDO and resistor R5, subsequently keeping transistor Q1 energized. If no further action occurs an internal timer contained within watchdog timer U11 will time-out after approximately 1.6 seconds and switch off Q2, causing Q1 to turn off and remove power from the scale's circuitry.
  • Page 15 MICROCOMPUTER AND SUPPORT CIRCUITS To attain various additional features such as automatic zero tare, pounds/kilograms conversion, weight lock-in, previous weight memory, etc., a microcomputer is employed to additionally process the data supplied by the A/D converter. This microcomputer system consists of U10, a microcomputer; U7, a peripheral port expander to furnish additional input/output lines;...

  • Page 16: Printer General Description

    RESET GENERATION In order for microcomputer U10 to properly execute its software instructions it must be initialized to the start of the program when power is first turned on. Reset pin 9 of U10 will accomplish this when it is set “high." A reset pulse of approximately 200 mS is automatically generated by "watchdog timer"...
  • Page 17 1 7/8" in diameter. One roll of paper will produce about 500 weight tickets. No ink ribbons are required. Additional rolls of paper can be purchased at many stationary supply stores or directly from Welch Allyn part number 23709.
  • Page 18 When any of the heater resistors are momentarily energized (powered for about 3 milliseconds) it will produce a small rectangular black dot on the thermal paper. Each printed character composition is 10 dots wide by 24 dots high. The paper width allows a maximum of 24 characters per line, which includes spaces between characters and paper edge margins.
  • Page 19 PRINTER MICROCONTROLLER & SUPPORT CIRCUITRY Microcontroller U202 is included to perform all the data manipulation and timing required to make the printer mechanism work. It contains RAM (random access memory), a flash ROM (read only memory) with program software, I/O (input/output) ports, a UART (universal asynchronous receiver/transmitter) and the needed arithmetic logic, clock generating, and associated internal logic.
  • Page 20 Note that STB2 and STB3 are joined together to divide the heater resistors into three, 128 heater resistor segments. U202 also controls the maximum number of heater resistors energized by assemblies using limiting the number of “on” dots in the dot data string sent to the thermal head. With the dot data now loaded into the thermal print head, microcontroller U202 controls the length of time the heater resistors are on, typically around 3-4 mS, to form the dot image on the paper.
  • Page 21 PRINTER PAPER SENSING AND HEAD POSITION The printer mechanism contains an optical paper sensor consisting of an infrared diode emitter and a complimentary phototransistor. Light from the infrared emitter reflects off the paper and is detected by the phototransistor at connector J207. Microcontroller U202 uses this signal to determine the presence or absence of paper and take action accordingly.

  • Page 22: Maintenance Of Scales

    Maintenance of Scales Routinely perform the following preventive maintenance to keep your scale in working order. 1. Check the calibration annually or as required. 2. Inspect the scale for cracks or loose mounting hardware. Replace or repair as necessary. 3. Visually inspect the scale enclosure for damage or loose or missing hardware. Replace or repair as necessary.

  • Page 23: Change The Printer Paper

    Change the printer paper 1. Use a screwdriver to loosen the screw on the battery access door and remove the printer access door. 2. Remove the spindle containing the empty printer paper roll from the printer paper well. 3. Replace the printer paper roll in the spindle. Make sure the new printer paper is advancing from the bottom of the roll.

  • Page 24: Calibration Of Scale

    Traction or physical therapy weights are NOT acceptable since their actual weight can often be in error as much as +/-10%. Calibration weights may be purchased from WELCH ALLYN or a local scale dealer. An alternative to calibration weights is the weight comparison method. This requires a known accurate, calibrated scale.
  • Page 25 Calibration Mode Enter the “calibration mode” by following exactly the procedure outlined below: 1. Be sure scale is off. The weighing platform must be in the “down” or operating procedure. 2. Press and hold the "RE WEIGH" pushbutton. 3. While pressing the "RE WEIGH" pushbutton press and release the "ON" pushbutton. 4.
  • Page 26 Using the specified three 25-kilogram test weights a difference of 165.3 +/- 0.1 pound should be obtained. If necessary, adjust potentiometer P1 (span adj.) on the instrument board until the correct value is obtained. Remove the test weight and recheck the zero offset value. Note that adjusting P1 may also alter the zero offset value.

  • Page 27: Stow-A-Weigh Scales Disassembling Guide

    Stow-A-Weigh Scales Disassembling Guide Required tools - 1/8” Allen wrench - Small Philips screwdriver - 5/16” socket - Small slotted screwdriver - 10 mm socket - 5 mm nut-driver - 3/8” socket - #1 Phillip screwdriver -3/8” wrench - ¼” ratchet driver with extension - ½”...

  • Page 28: 5202 Disassembly

    5202 Disassembly: 1. Use a #1 Phillip screwdriver to remove the battery access door’s screws 2. Remove batteries 3. Use a 1/8” Allen wrench to remove the screws on the display panel...
  • Page 29 4. Disconnect J1 5. Disconnect three-pins harness 6. Disconnect J14...
  • Page 30 7. Disconnect J4 8. Use a 5/16” socket to remove the nuts 9. Disconnect J6...
  • Page 31 10. Use a #1 Phillip screwdriver to remove the screws on the board 11. Use a #1 Phillip screwdriver to remove the screws on the display board 12. Disconnect blue-ribbon cable...
  • Page 32 13. Use a 1/8” Allen wrench to remove the screws on the panel cover 14. Use a small Philips screwdriver to remove the screws on battery holder...
  • Page 33 15. Use a 1/8” Allen wrench to remove the screws on the left and right leg cover 16. Use a #1 Phillip screwdriver to remove screws on the momentary switch...
  • Page 34 17. Use a #1 Phillip screwdriver to remove the bracket mount’s screws Use a 3/8” wrench to remove the nuts...
  • Page 35 18. For replacement of the shock absorber and the ball mounts, use a small slotted screwdriver to push the latch on the shock absorber’s socket down (for the top) and up (for the bottom) Remove the shock absorber by pulling it away from the ball Use a ½”...
  • Page 36 20. Use a 5/16” socket to remove the screws on the wire with loop and the cable clamp 21. Use a #1 Phillip screwdriver to remove the screws Use a 3/8” wrench to remove the nuts of the bracket 22. Use a 5 mm nutdriver to remove the screws on the RS232 port...
  • Page 37 23. Use a 1/8” Allen wrench to remove the screws on the deck cover 24. Disconnect the wire harnesses 25. Use a #1 Phillip screwdriver to remove the screws on the board NOTE: Remove the tape or cable clamps that hold the load cell and the wire in place to the weldment...

  • Page 38: 6202 & 6202D Disassembly

    26. Use a 3/8” socket to remove the nuts on each load cell CAUTION: Do not apply extra force to the base of the scale. The load cell capacity can overload and cause damage to the load cells. 6202 & 6202D Disassembly: 1.
  • Page 39 3. Use a 1/8” Allen wrench to remove the screws on the readout assembly 4. Disconnect J1 5. Disconnect JTEST...
  • Page 40 6. Disconnect J4 7. Disconnect J15 8. Disconnect three-pins harness...
  • Page 41 9. Use a 5/16” socket to remove the nuts 10. Disconnect J6 11. Use a #1 Phillip screwdriver to remove the screws on the board...
  • Page 42 12. Use a #1 Phillip screwdriver to remove the screws on the display board 13. Disconnect blue-ribbon cable 14. Use a 1/8” Allen wrench to remove the screws on the front panel...
  • Page 43 15. Use a small Philips screwdriver to remove the screws on the battery holder 16. Use a small slotted screwdriver to loosen the screws on the wire harnesses and pull the wires out 17. Use a #1 Phillip screwdriver to remove the screws...
  • Page 44 18. Use a 1/8” Allen wrench to remove the screws on the left and right leg cover 19. Use a #1 Phillip screwdriver to remove the bracket mount’s screws Use a 3/8” wrench to remove the nuts...
  • Page 45 20. Use a 3/8” wrench to remove the nuts on the mounting bracket 21. For replacement of the shock absorber and the ball mounts, use a small slotted screwdriver to push the latch away Remove the shock absorbers by pulling it away from the ball mount Use a ½”...
  • Page 46 22. Printer disassembly: Disconnect J201 and J202 23. Use a #1 Phillip screwdriver to remove the screws on the printer board 24. Disconnect J204, J207, J206, J203...
  • Page 47 25. Use a 5/16” socket to remove the nuts on the printer mechanism assembly four screws 26. Use a #1 Phillip screwdriver to remove the screw on the printer cover Use a small Philips screwdriver to remove the smaller screws...
  • Page 48 27. Use a #1 Phillip screwdriver to remove the screws on the power connector assembly 28. Use a small slotted screwdriver to remove the wired connectors 29. Use a 10 mm socket to remove the AC power jack...
  • Page 49 30. Use a 5/16” socket to remove the screws on the AC power cable clamp 31. Use a 1/8” Allen wrench to remove the deck cover’s screws 32. Disconnect the wire harnesses...
  • Page 50 33. Use a #1 Phillip screwdriver to remove the board’s screws NOTE: Remove the tape or cable clamps that hold the load cell and the wire in place to the weldment 34. Use a 3/8” socket to remove the nuts on the load cells CAUTION: Do not apply extra force to the base of the scale.

  • Page 51: Satellite Base Disassembly (6202D Only)

    Satellite base disassembly (6202D only): 1. Use a 1/8” Allen wrench to remove the screws on the panel covers 2. Use a small Philips screwdriver to loosen the screws of the black plugs to remove the wires...
  • Page 52 3. Use a #1 Phillip screwdriver to remove the screws on the board 4. Use a 5/16” socket to remove the nut on the cable clamp 5. Use a 1/8” Allen wrench to remove the screws on the left and right leg cover...
  • Page 53 6. Use a 3/8” wrench to remove the nuts on the mounting bracket 7. For replacement of the shock absorber and the ball mounts, use a slotted screwdriver to push the latch down. Remove the shock absorbers by pulling it away from the ball mounts Use a ½”...
  • Page 54 8. Use a #1 Phillip screwdriver to remove the screws on the momentary switch 9. Use a 1/8” Allen wrench to remove the deck cover’s screws 10. Disconnect the wire harnesses...
  • Page 55 11. Use a #1 Phillip screwdriver to remove the board’s screws NOTE: Remove the tape or cable clamps that hold the load cell and the wire in place to the weldment 12. Use a 3/8” socket to remove the screws on the load cells CAUTION: Do not apply extra force to the base of the scale.

  • Page 56: Troubleshooting

    Troubleshooting Scale Troubleshooting The following simplified trouble shooting procedures are recommended for identifying defective system components. Certain corrective measures are provided. More complicated servicing should only be performed by the factory or authorized service facilities. Most problems can be solved over the telephone. Problems requiring factory service are usually handled quickly and the scale is on its way back.

  • Page 57: Printer Troubleshooting

    READING DOES NOT CHANGE WHEN WEIGHT APPLIED The platform cable, connector or a load cell transducer may be defective. The load cell transducer's resistance can be checked with an ohmmeter after unplugging from the junction board. The proper resistance values are listed below. Note that these numbers are for individual load cells that are unplugged from the junction board.
  • Page 59 NO PRINT, ONE LONG BEEP This indicates the printer did not respond to the scale’s request for printing. This can be caused by the printer being out of paper or the printer head switch being in the "UP" (open) position. Observe the printer status lamp, LED D202, on the printer interface board;...

  • Page 60: Symptoms And Solutions

    PRINTER STATUS LIGHT FLASHES RED The printer status lamp will change color from green to red if a problem is detected. It will also flash a predetermined number of times to indicate the cause of the malfunction. The flashing sequence is described below: One flash: Needs paper.
  • Page 61 Symptom Possible Cause Corrective Action Display Replace necessary components Board/Mainboard Cracked Battery Holder Replace the Battery Holder Assembly. Note Black and White Wire that was unhooked from the faceplate pulls out with the Battery Holder & Bracket Assembly Platform is falling open Damper Ring or Replace damper and spring...
  • Page 62 Symptom Possible Cause Corrective Action 1. Test for +5 Volts across pins 1 and 8 of JTest connector, for VR1, after pressing the “On” button. 2. Test for +5 volts on VR2 Regulator Pin 3 for the Voltage to Microprocessor and the Display board, if no + 5 Volts, replace regulators, VR1, or VR2.
  • Page 63 Symptom Possible Cause Corrective Action If Scale turns on replace the switch assembly. Follow the below instructions to replace the switch assembly. 1. Remove front panel switch assembly, there are two Screws on top of front panel with 1/8” Allen Key. 2.
  • Page 64 Symptom Possible Cause Corrective Action 2. Turn scale on IF Scale displays “Cable” or “O-Load” Replace the MAST Cable IF Scale display remains at “0.0” 1. Test with DC Volt Meter across pins 1 and pin 7 of JTest  Voltage .985 or +/- .01 and stable 2.
  • Page 65 Symptom Possible Cause Corrective Action The corner that reads the lowest is the problem area. Repeat corner test if need be. Inaccurate Load Cell/Calibration OHM out Load Cells - See trouble shooting section in this Weights - Scale Manual not weighing correctly, scale Bad A/D Chip Turn off the scale - Hold "REWEIGH"...
  • Page 66 Symptom Possible Cause Corrective Action Weight Memory Chip or U9 and EM1033 or Microprocessor – Replace the Main Board Remains the Microprocessor same Unable to Cold Solder on the Check Gain Resistor R24 on the Cal Chip, Replace Cal chip if Calibrate Calibration Plug necessary.
  • Page 67 Symptom Possible Cause Corrective Action Load" Flashes 1. Remove Front Panel - Top of Faceplate (need 1/8” Allen or Beeps key) 2. Check the green, white, black and red cable to make sure that it is connected to the J4 Load Cell 6 pin connector 3.
  • Page 68 Symptom Possible Cause Corrective Action Not printing, Too much paper is Have to remove paper from roller and redress paper in roller of Paper not printer mechanism. curled up inside on coming out of roller printer Orientation In-Floor Scales Only – Re-orient the Printer door for Tearing of thermal paper.

  • Page 69: Repair Parts List

    Symptom Possible Cause Corrective Action Printer Mechanism Replace Printer Mechanism Repair Parts List PART NO. DESCRIPTION PART NO. DESCRIPTION 23709 Thermal Printer Paper (Box 15 rolls) 630198 BATTERY HOLDER/SWITCH HARNESS, 5202 40408 BHSCS 10-32 X 3/8 18-8 STAINLESS STEEL 630203 HARNESS ASSY EXTERNAL POWER 41013 CONNECTOR, 5 PIN PANCON CE100F24-5-CB...
  • Page 70 710046W HARNESS, INTERIOR LOADCELL 412319 ASSY 700051 MAIN PCBA, 5202, KG 710050W HARNESS, 22" INTERIOR LOAD CEL 412328 ASSY 700116 MAIN PCBA FOR 6202, KG 710051W HARNESS, 6202D SWITCH 412256 ASSY 700116 MAIN PCBA FOR 6202 STD 710052W HARNESS, INTERNAL CONNECTING 412360 ASSY 700116 MAIN PCBA FOR 6202, KG, PRT 710059W...

  • Page 71: Schematics & Part Diagrams

    Schematics & Part Diagrams...

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