AKG PT 300 Servisní příručka

I PT300 Service ManualA & A Scales1-813-994-3190Fax 509-355-3498www.stainlessscales.com

PT300, Service ManualRev B, October, 20009Theory of OperationFor the following discussion, please refer to the schematics in appendix B.Power supply:T

PT300, Service ManualRev B, October, 200010Charger:The battery charger works on the constant voltage charging principle. The diodeD4 is a 10 volt zen

PT300, Service ManualRev B, October, 200011Low Voltage Sensor:R9, D7, and Q2 work much the same as R6, D6 and Q5 in the power switchsection. The addi

PT300, Service ManualRev B, October, 200012Analog Section:The analog section takes the signal from the load cells (about 10 mV) and translatesthis sig

PT300, Service ManualRev B, October, 200013Auto ZeroIntegrateDeintegrateU17 Pin 1Auto ZeroFigure 5 Conversion CycleLet’s examine the operation of the

PT300, Service ManualRev B, October, 200014Now for the messy details of implementation; U17 is driven through theintegrate, deintegrate, and auto-zero

PT300, Service ManualRev B, October, 200015Display Driver:Any LCD display must be driven by a waveform with a net zero DCvoltage. If the driving volt

PT300, Service ManualRev B, October, 200016TroubleshootingCautionChanging some parts may cause a large change in calibration whereas others may ormay

PT300, Service ManualRev B, October, 200017Scale shuts off.Normally the scale shuts itself off after a long period of inactivity. The length oftime i

PT300, Service ManualRev B, October, 200018Low batt indicator won't turn off.It is possible that the output from the batteries is really low. Lo

PT300, Service ManualRev B, October, 20001SAFETY SUMMARYThe following general safety precautions must be observed during all phases ofoperation, servi

PT300, Service ManualRev B, October, 200019Tests, Waveforms andVoltage measurementsBlank EPROM test.One of the most challenging problems is finding a

PT300, Service ManualRev B, October, 200020CLKRDMI__WRRFSH_____0038hRFSHSee BelowSee Below0FFh?039h00hFigure 7 Blank EEPROM Test WaveformsFor the firs

PT300, Service ManualRev B, October, 200021A15 20mS/DivA14 10mS/DivA13 5mS/DivA12 2mS/DivA11 1mS/DivA10 0.5 mS/DivA09 0.1mS/DivA08 50mS/DivA07 0.1mS/D

PT300, Service ManualRev B, October, 200022System checkout procedureThe following measurements are typical values. When tolerances are given the sign

PT300, Service ManualRev B, October, 200023If the display backplane drive is missing, TURN THE SCALE OFF IMMEDIATELY.Operation without a backplane sig

PT300, Service ManualRev B, October, 200024SIO (totalizing):To test the totalizing function you will need 2 scales (one is the scale under test)and a

PT300, Service ManualRev B, October, 200025Turn both scales off. Now put the scale under test in the slave position and the otherscale in the master

PT300, Service ManualRev B, October, 200026Load Cells:Each PT300 scale has two load cells. These load cells are the transducers thatconvert mechanica

PT300, Service ManualRev B, October, 200027ProceduresPlease see Parts section for the parts drawing.Loading pads & blocks.At several points in the

PT300, Service ManualRev B, October, 20002811) Apply 5000, 10000, 15000, and 19000 lbs and verify span is within 1.0% ofapplied load. Make any adjust

PT300, Service ManualRev B, October, 20002Table of ContentsSCOPE OF MANUAL...

PT300, Service ManualRev B, October, 200029Remove and replace main circuit boardTools requiredTwenty thousand pound calibration press.8" x 8"

PT300, Service ManualRev B, October, 200030Remove and replace load cellTools requiredTwenty thousand pound calibration press.8" x 8" x 2 ± .

PT300, Service ManualRev B, October, 200031Assembly16) Set new load cell in place.17) Glue the load cell lead off to the side so it doesn’t run under

PT300, Service ManualRev B, October, 20003212Figure 13 Load Cell Placement1) Remove all 10 bezel screws.2) Detach keyboard assembly and set aside. Do

PT300, Service ManualRev B, October, 200033the battery tube and the printed circuit board.17) Install tow board mounting screws.18) Check and adjust c

PT300, Service ManualRev B, October, 200034Unpacking and InstallationCaution:Keep all packing materials in case scale must be shipped again. If the p

PT300, Service ManualRev B, October, 200035Spare keypad.Main circuit board.Summing board.Load Cells.Check straps.Charging transformer.Span resistors,

PT300, Service ManualRev B, October, 200036Connector pinoutsA: +5VB: - InputC: GroundD: - OutputE: +12V (Charging Voltage)F: + InputG: UnusedH: + Outp

PT300, Service ManualRev B, October, 200037PT300 Main Circuit BoardParts ListPT300 Circuit Board Reference: Quantity:1.22Mhz Crystal 1Liquid Crystal D

PT300, Service ManualRev B, October, 2000384.7K ohm ¼ w 5% R5,R31 210K ohm ¼ w 5% R6,R9,R10,R32 410K ohm ¼ w 1% R14 147K ohm ¼ w 5% R50 1100K ohm SIP,

PT300, Service ManualRev B, October, 20003Low batt indicator: ...

PT300, Service ManualRev B, October, 200039PT300 SUMMING CIRCUIT BOARD PARTS LISTPT300 Summing Board Rev. 1 Reference: Quantity:14pin Dual Row, 90º, H

PT300, Service ManualRev B, October, 200040Appendix ASetting the deadload.The output signal from the load cells is set to a value slightly above zero

PT300, Service ManualRev B, October, 2000411) It is assumed that the scale is disassembled with the main circuit boardremoved from the case (but still

PT300, Service ManualRev B, October, 200042Selecting the Initial Span Range.It may be necessary to change the span resistor if you run out of travel w

PT300, Service ManualRev B, October, 200043Schematics and Parts layoutNumber Title Pages072391-102 PT300 Schematic 3None PT300 Board Assembly 1None PT

PT300, Service ManualRev B, October, 200044Appendix BSchematics

PT300, Service ManualRev B, October, 200045

PT300, Service ManualRev B, October, 200046

PT300, Service ManualRev B, October, 200047Totalizing cable

PT300, Service ManualRev B, October, 200048Charging Cable

PT300, Service ManualRev B, October, 20004Table of IllustrationsFIGURE 1 BLOCK DIAGRAM...

PT300, Service ManualRev B, October, 200049Loadcell and Summing Board

PT300, Service ManualRev B, October, 200050Internal Cable Assembly

PT300, Service ManualRev B, October, 200051Parts

PT300, Service ManualRev B, October, 20005Scope of manualThis service manual describes the Intercomp PT300 scale specifications, theory ofoperation, i

PT300, Service ManualRev B, October, 20006SpecificationsElectricalDisplay settlingtime:950 milliseconds to typical reading (static).Accuracy: ±1% of a

PT300, Service ManualRev B, October, 20007All metal case provides EMI/RFI immunity.Caution The scale and connecting cables should be operated at a min

PT300, Service ManualRev B, October, 20008Figure 1 Block DiagramPower Supply BatteryDriversLow Battery SensorOn OffLampLb/KgZeroHold/RelTotal/LocalPri