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Sharp PC-1350 Troubleshooting Guide

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Sharp PC-1350 power and LCD bias circuit (service manual)
The PC-1350's power and LCD bias circuit (Sharp service manual).

Fault-finding for the Sharp PC-1350. Sharp's service manual gives current limits, cell replacement thresholds, a display and key test using a test RAM card, the re-initialisation needed after a cell change, and circuit diagrams with circuit designators, so most faults can be traced with a multimeter and a bench supply.[1][2][3]

Preliminary checks

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  • Check the cells. Sharp says the PC-1350's pair needs replacing below 5.2 V (2.6 V per cell), and a RAM card's CR2025 below 2.5 V.[1]
  • Check that the RAM card lock switch is at LOCK. The PC-1350 does not work otherwise.[4]
  • Try the machine with the RAM card removed.
  • Save anything important first: initialising the PC-1350 with a RAM card fitted clears the card.[3]

After a cell change

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A PC-1350 that shows meaningless characters, or whose serial port misbehaves, after a cell change may not have been initialised. Sharp's procedure: remove the RAM card, switch on, press RESET, then enter CALL &EF88 (serial I/O) and POKE &6EAF, 0 (display), each followed by ENTER, and check for the RUN MODE screen with the prompt. Repeat if necessary, then refit the card.[3]

Current consumption

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Sharp's current limits at 20 °C[1]
Condition Maximum
PC-1350, power off 20 µA
PC-1350, displaying 500 µA
PC-1350, calculating 5 mA
CE-202M RAM card About 8.4 µA

A PC-1350 that drains its cells in storage should be measured with the power off against the 20 µA limit, with the RAM card removed and then fitted.

RAM card current test

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Sharp's test for a RAM card: connect an ammeter between the two ends of the card's battery pads, apply 3 V DC, and read the current after three seconds. It should settle below the values in the table; a few tens of microamps immediately after power-on can be ignored.[5]

RAM card current limits (3 V supply)[5]
Card Board type Maximum
CE-201M Flat package LSI 4.0 µA
CE-202M PCOS (chip bonded to the board) 7.0 µA
CE-202M Flat package LSI 8.4 µA

A card that draws more than this will flatten its CR2025 early and lose its contents.

Display and key test

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Sharp's service test uses a test RAM card (part UKOGC1010CSZZ). With the card fitted, CALL &5000 and ENTER puts a dot pattern on the display; the program then checks that keys are pressed in a set order and reports any key that is missed by its key code.[2] Without the test card, check the display for missing dots or lines and press every key in turn.

Display symptoms
Symptom Check
Blank display Cells against 5.2 V; RAM card lock switch at LOCK; then current consumption[1][4]
Meaningless characters after a cell change Run Sharp's initialisation (CALL &EF88, POKE &6EAF, 0)[3]
Faint or uneven display Adjust VR1 (20 kΩ); check C2 to C4 and the R10 to R13 divider[6][7]
Missing dots, lines or a block The LCD connects through a PWB-LCD connector (part PGUMS1550CCZZ); clean and reseat it before suspecting the LCD or its SC43537 driver[8]

Error codes

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The PC-1350's hard cover carries Sharp's error guide: 1 syntax error, 2 calculation error, 3 illegal function argument, 4 too large a line number, 5 NEXT without FOR or RETURN without GOSUB, 6 memory overflow, 7 PRINT USING error, 8 I/O device error, 9 other errors.[9] Error 8 is the one that points at hardware: check the connected peripheral, its cable and its power.

Serial port

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The 15-pin serial port works at CMOS levels (4 to 6 V), asynchronous and half duplex at 300, 600 or 1200 baud.[10] It is not an RS-232 port: Sharp Pocket Computers describes level converters for connecting this 15-pin port to RS-232 equipment.[11] If the port misbehaves after a cell change, run the initialisation above, which includes CALL &EF88 for the serial I/O.[3]

Board level

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The circuit diagrams carry designators. On the main board, C1 (3.3 µF) sits across the supply from the two CR2032 cells, which feed through R1 and the BD1 diode pair; VR1 sets the LCD drive voltage; and R10 to R13 with C2 to C4 make the LCD bias levels.[6][7] The processor is an SC61860A13 with a 768 kHz crystal, and the SC60220 gate array decodes the RAM and display chip selects.[8][12]

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Sharp, Service Manual, PC-1350, section 4 "Battery life and power consumption", printed page 3 (PDF page 3).
  2. ↑ 2.0 2.1 Sharp, Service Manual, PC-1350, "Display and key input tests", printed page 5 (PDF page 5), with the key code chart on printed page 6.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Sharp, Service Manual, PC-1350, "Supplement & correction": checking the operation when replacing the battery cells (PDF page 36).
  4. ↑ 4.0 4.1 Sharp, Service Manual, PC-1350, section 6 "Cautions in using the RAM card option", printed page 3 (PDF page 3).
  5. ↑ 5.0 5.1 Sharp, Service Manual, PC-1350, section 9 "RAM card": CE-201M/202M power consumption test, printed page 12 (PDF page 12).
  6. ↑ 6.0 6.1 Sharp, Service Manual, PC-1350, section 10 "Circuit diagram (1)", printed page 13 (PDF page 13).
  7. ↑ 7.0 7.1 Sharp, Service Manual, PC-1350, section 11 "Parts and signal layout chart (main PWB)", printed page 17 (PDF page 17).
  8. ↑ 8.0 8.1 Sharp, Service Manual, PC-1350, parts list, main PWB unit (PDF page 29): PWB-LCD connector PGUMS1550CCZZ, SC43537LDN, SC60220, SC61860A13, crystal 768 kHz.
  9. ↑ Photograph of a PC-1350 and its hard cover, File:Sharp PC-1350.jpg (Frcoe, public domain, via Wikimedia Commons): the "Error guide" printed on the cover.
  10. ↑ Sharp Corporation, Service Manual, PC-1350, code 00ZPC1350SM/E, September 1984, section 1 "Specifications", printed page 1 (PDF page 1): serial I/O. Hosted as File:Sharp PC-1350 Service Manual.pdf.
  11. ↑ Sharp Pocket Computers, Printers, Cables, Level Converters & Accessories, sharppocketcomputers.com—link(accessed 2026-10-21) "Level Converters" section: converters change the 5 V logic levels to RS-232 ±12 V or RS-422, for calculators with the 15-pin SIO connector.
  12. ↑ Sharp, Service Manual, PC-1350, section 8 "LSI descriptions", printed pages 7 to 11 (PDF pages 7 to 11).


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