Welch Allyn 4802D Service Manual
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Welch Allyn 4802D Service Manual

Pediatric/infant scale
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Welch Allyn Pediatric/Infant Scale 4802D
Scale
Service Manual
Model 4802D – Pediatric/Infant Scale

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Summary of Contents for Welch Allyn 4802D

  • Page 1 Welch Allyn Pediatric/Infant Scale 4802D Scale Service Manual Model 4802D – Pediatric/Infant Scale...
  • 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 Custom setup ..............................4 Enter Advanced Service Mode ........................6 MAINTENANCE OF SCALES ..........................7 Technical support services ..........................7 Warranty service ............................7 Non-warranty service ............................ 8 TROUBLESHOOTING OF SCALES ........................15 BATTERY REPLACEMENT ..........................17 Symptoms and solutions ..........................17 CALIBRATION OF SCALES..........................

  • Page 4: Custom Setup

    Custom 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. Make sure the scale is powered down 2.
  • Page 5 This option determines the audible signal that occurs when a front panel button is pressed. 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. OutPut* This option displays the current data port output option. Detailed instructions for this feature are available from Welch Allyn.

  • Page 6: Enter Advanced Service Mode

    PC brd* This option displays the model number of the printed circuit board. A second press of DATA SEND displays the revision of the printed circuit board. SEt-UP This option is displayed when you have cycled through all the options. Press and hold ON to power down the scale.

  • Page 7: Maintenance Of Scales

    Do not service or perform maintenance while the scale is in use with a patient. Technical 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: Non-Warranty Service

    To ensure safe receipt of your device by the service center and to expedite processing and return of the device to you, thoroughly clean all residues from the device before you ship it to Welch Allyn. For cleaning requirements, see the Cleaning instruction in the Directions for Use.
  • Page 9 MODELS 4802D The load cell employed in the model 4802D is referred to as a "Double Ended Bending Beam" ("DEBB")”. It is constructed as a double bending beam with two strain gauges, forming a "half-bridge", mounted on each end of the beam, where the bending takes place in response to weight applied.
  • Page 10 Capacitors C16/C17/C24 provide local bypassing of the power supplies used by instrumentation amplifier U4. Capacitor C18 furnished compensation of U4 by reducing amplification at higher frequencies. ADDITIONAL AMPLIFICATION AND SIGNAL FILTERING Components for an optional second gain stage may be added on the printed circuit board. If included, operational amplifier U5 is used to provide additional gain and signal filtering.
  • Page 11 120 KHz. POWER SWITCHING, VOLTAGE REGULATION AND SUPPORT CIRCUITRY Depending upon their configuration, WELCH ALLYN second generation scales may contain disposable primary cells. Additional circuitry is included to switch the battery supply, provide voltage regulation and detect low battery voltage conditions.
  • Page 12 pushbutton closure is also coupled through diode D3 (located on the display board) to signal input pin "P1" of I/O expander U4 (located on the display board) that the "RECALL PRIOR WEIGHT" pushbutton is pressed. 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.
  • Page 13 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; U9, a non-volatile memory which stores the previous weight reading;...
  • Page 14 A reset pulse of approximately 200 mS is automatically generated by “watchdog timer” U11 when the Vcc level rises above 4.65 volts. If Vcc is below 4.65 volts, the reset line stays “high”, keeping the microcomputer U10 in an inactive state. BEEPER A small audio annunciator is driven by transistor Q5, which in turn is controlled by U10's output pin P2.3.

  • Page 15: Troubleshooting Of Scales

    with U4 to look at the condition of the switches on the front panel. A closed switch will be detected by U10's software. If the switch remains closed for a period of time it will be validated by U10 ("debounced") and the appropriate action called for will be executed.
  • Page 16 WHT(3) TO RED(4) 325-375Ω Consult Welch Allyn if readings differ from those shown. NOTE: Ohmmeters will not indicate a change in resistance of the load cell transducer when weights are applied to scale. This is due to the extremely small change in resistance of the strain gauges employed (<1 ohm) and the fact that the bridge configuration presents a constant value of resistance when measured from its terminals.

  • Page 17: Battery Replacement

    BATTERY REPLACEMENT CAUTION Use only size D disposable alkaline batteries. The use of any other battery will void the warranty. 1. Remove the cradle from the scale. 2. Remove the top cover of the enclosure by removing the eight hex screws with a 1/8- inch allen wrench.
  • Page 18 “Data Send” Immediately press and release button 5 times quickly Puts scale in the "Cal" Mode. Note: newer 4802D units S-T logo became the “Print/Send/Data “or the “Send Data” button. “Data Send” button one more time to show A/D reading.

  • Page 19: Calibration Of Scales

    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 20: Enter Calibration Mode

    1. Unplug the scale from the AC line. 2. Unplug the cradle from the scale. 3. Detach the top cover of the scale's enclosure by removing the eight (8) #10 button head screws. 4. The scale's instrument board should now be in full view. Note the location of the trimmer potentiometer, "P1 Span".

  • Page 21: Repair Parts List

    COVER, CABINET-4802 48118 FERRULE FOR 3/8" HANDLE 48205 Mounting post (for cradle) 48217 Scale liners, carton of 500 48222 CRADLE OVERSIZED FOR 4802D 48502 Load cell transducer DEBB- 100 48503 Loading arm 66011 Rubber foot w/ washer 255002 CALIBRATION PLUG – 4802...

  • Page 22: Warranty

    Harness, 12V Ext Power Supply 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.
  • Page 23 The warranty period shall start on the date of purchase. The date of purchase is: 1) the invoiced ship date if the device was purchased directly from Welch Allyn, 2) the date specified during product registration, 3) the date of purchase of the product from a Welch Allyn authorized distributor as documented from a receipt from said distributor.

  • Page 24: Schematic's

    SCHEMATIC’s...
  • Page 25 PCB ASSEMBLY 700056W...
  • Page 26 PCB ASSEMBLY 700059 HARNESS ASSEMBLY 710031...

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