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Sharp PC-1500A Troubleshooting Guide

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Sharp PC-1500A main board power section (service manual)
The power input section of the PC-1500A main board: the 1SS98 and 1S1588 diodes, the two 10 V 220 µF capacitors and the regulator module pads (Sharp PC-1500A service supplement).

Fault-finding for the Sharp PC-1500A. Sharp's PC-1500A service supplement covers only what differs from the Sharp PC-1500, and marks the key and power supply circuit "same as PC-1500".[1][2] The supply voltages, the all-reset procedure, the key matrix, the FPC replacement and the error codes are therefore those in the Sharp PC-1500 Troubleshooting Guide. The sections below cover what differs on the PC-1500A and how the PC-1500 checks apply to it.

What is different on the PC-1500A

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Differences that matter for fault-finding[1][3][2]
Area PC-1500 PC-1500A
RAM chips One HM6116 user RAM and two TC5514P system RAM Four HM6116; no TC5514P
BASIC program and data area 1850 bytes 5946 bytes
Machine language area None 1024 bytes
40-pin connector chip selects S1, S2, S3 S3, S4, S5
Power regulator module EHM718L70 MA1066 or EHM718L70
System ROM part SC613128FN SC613128F4

All keys dead

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Use Sharp's all-reset procedure exactly as on the PC-1500: hold ON/BREAK, press the ALL RESET switch on the underside with a ball-point pen for about 15 seconds, wait for NEW0?: CHECK, then press CL and enter NEW0. It clears the program, data and reserve area.[4][5] The step-by-step procedure and the causes Sharp gives are in the PC-1500 guide.

Power supply

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Because the circuit is the same, measure the PC-1500A against the PC-1500 figures: VGG 4.7 V, VCC 4.7 V ±0.02 V and VDISP 3.7 V ±0.01 V at 25 °C.[6][2] The PC-1500A supplement's circuit diagram names the regulator "Hi-MIC (MA1066 or EHM718L70)", so a PC-1500A may carry either module. Check which is fitted before looking for a donor.[2]

The order of checks (cells under load, VBAT, VGG, VCC with ON pressed, then VDISP) and the module pin numbers are in Power supply diagnostics in the PC-1500 guide. On the PC-1500A board the two 220 µF capacitors are beside the 1SS98 and 1S1588 diodes, as on the PC-1500.[7]

Memory faults

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The PC-1500A's user RAM is four HM6116 chips. A RAM fault on a PC-1500A therefore involves those four chips. The PC-1500's TC5514P system RAM pair is not fitted.[1]

  • If programs or variables are corrupted while the cells are good and the machine has been reset, suspect the RAM chips and their supply.
  • If the problem appears only with a module fitted, try the machine without it and try the module in another machine. Sharp says all PC-1500 options can be used with the PC-1500A; its supplement renames the module connector's chip-select lines S3, S4 and S5.[1]

Reset faults

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The PC-1500A has the same two 50 V 1 µF capacitors in the power-on reset circuit as the PC-1500. On the PC-1500A board both sit beside the reset terminal.[7][8] A machine that powers up into garbage, or needs the all reset every time, may have a failed reset capacitor; see Sharp PC-1500A Capacitor Replacement Guide.

Keyboard and display

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The key matrix, the FPC replacement and the display checks are the same as on the PC-1500; see the keyboard and display sections of the PC-1500 guide.[1] The PC-1500A's key board and main board have their own part codes, DUNTK7529CCZZ and DUNTK7530CCZZ.[3]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sharp Corporation, Model PC-1500A Service Manual, October 1982, sections 1 to 3 (PDF page 2): RAM change, specification change, 40-pin connector signal names, compatibility. File:Sharp PC-1500A Service Manual.pdf.
  2. ↑ 2.0 2.1 2.2 2.3 Sharp, Model PC-1500A Service Manual, section 5 "PC-1500A key & power supply circuit (same as PC-1500)" (PDF page 4): "Hi-MIC (MA1066 or EHM718L70)".
  3. ↑ 3.0 3.1 Sharp, Model PC-1500A Service Manual, section 4 "Parts list & guide" (PDF page 3): VHiMA1066 power regulator; VHiSC613128F4; key and calculation board units.
  4. ↑ Sharp, Service Manual, Model PC-1500 & Option, section 5 "Servicing", printed page 19 (PDF page 21).
  5. ↑ Sharp, PC-1500 instruction manual, "Trouble-shooting" (PDF page 4). File:Sharp PC-1500 Instruction Manual.pdf.
  6. ↑ Sharp Corporation, Service Manual, Model PC-1500 & Option, February 1982, "6) Power supply circuit", printed page 18 (PDF page 20). File:Sharp PC-1500 Service Manual.pdf.
  7. ↑ 7.0 7.1 Sharp, Model PC-1500A Service Manual, section 7 "PC-1500A main P.W.B." (PDF page 8).
  8. ↑ Sharp, Service Manual, Model PC-1500 & Option, section 9 "Main circuit diagram", printed page 24 (PDF page 28): the reset circuit.


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