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Sharp PC-1350 General Maintenance

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Sharp PC-1350
A PC-1350 with its hard cover (photo: Frcoe, public domain)

Routine care of the Sharp PC-1350. The machine runs at about 6 V from two CR2032 lithium cells, and each RAM card has its own CR2025 cell, so maintenance is mostly about cells, the re-initialisation Sharp specifies after a cell change, and the RAM cards.[1] There is no mains voltage inside.

Cells

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PC-1350 cells (Sharp service manual)[1][2]
Item PC-1350 CE-201M / CE-202M RAM card
Cell Two CR2032 lithium, 200 mAh, about 6.0 V One CR2025 lithium, 120 mAh, about 3.0 V
Replace when below 5.2 V (2.6 V per cell) 2.5 V
Life About 250 hours of use; memory kept about 7 months with the power off (about 6 months with a CE-202M fitted) Contents kept about 34 months (CE-201M) or 18 months (CE-202M)

Measure the cells under load if the machine misbehaves; the 5.2 V threshold is for the pair.[1]

After replacing the PC-1350's cells

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Sharp's service manual supplement gives this check after a cell change:[3]

  1. Remove the RAM card first. If the PC-1350 is initialised with the card in place, the card is initialised too and its program and data are cleared.
  2. Set the power slide switch to ON and press the RESET button on the underside to clear the computer.
  3. Enter CALL &EF88 and press ENTER, then POKE &6EAF, 0 and press ENTER.
  4. Check that the display shows RUN MODE, the two commands and the prompt. If it does not, repeat the steps.
  5. Refit the RAM card.

CALL &EF88 initialises the serial I/O and POKE &6EAF, 0 initialises the display. Sharp says that without them the display may show meaningless characters and equipment on the serial port may not work properly.[3]

RAM card cells

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  • The CR2025 is inside the card package and has to be fitted with the special battery removing tool supplied with the card.[4]
  • If the card's cell is replaced while the card is in the PC-1350, the program data is not lost.[1]
  • Replace the card cell when it reads below 2.5 V.[1]

For corrosion from a leaking cell, see Battery Explosion, Capacitor or Corrosion Damage.

RAM cards

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  • The PC-1350 does not work unless the RAM card lock switch is turned to LOCK.[5]
  • Variables are erased when the card is removed unless MEM "C" has been executed to keep them on the card.[5]
  • The PC-1350's lock switch is wired so that operating it during auto power-off, or while the machine is running, breaks into the program and switches the power off, to protect the card's contents when it is changed.[6]
  • The CE-201M and CE-202M cannot be used in the Sharp PC-1360.[7]

If a card's board has to be taken out of its case, Sharp's manual warns that bending it can curl the terminals and cause contact failure. Straighten it with a slight curl the opposite way, clean the board and the tape area with alcohol, fix it back with fresh tape and wipe the terminals with alcohol.[4]

Contrast

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The contrast is set by VR1, a 20 kΩ variable resistor in the LCD supply circuit.[8][6] If the display is faint with fresh cells, adjust it before suspecting the LCD.

Cleaning and handling

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  • Wipe the case with a soft, dry cloth.
  • Keep the 11-pin peripheral connector and the 15-pin serial connector clean and dry.[9]
  • Take the cells out if the machine will be stored for a long time, but remember that the memory is lost.
  • The logic is CMOS; use an anti-static strap when the case is open.[10]

Capacitors

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The main board has four small polarised capacitors: C1 (3.3 µF) across the supply and C2 to C4 (1 µF each) in the LCD bias circuit.[6] See Sharp PC-1350 Capacitor Replacement Guide.

Preventive maintenance checklist

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  1. Save programs to tape before any cell work, or keep them on a RAM card with a good cell.
  2. Check the PC-1350 cells against 5.2 V and the RAM card cell against 2.5 V.
  3. After a cell change, remove the RAM card, reset and run the two initialisation commands.
  4. Check the RAM card lock switch.
  5. Check the contrast with fresh cells.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sharp, Service Manual, PC-1350, section 4 "Battery life and power consumption", printed page 3 (PDF page 3).
  2. ↑ Sharp, Service Manual, PC-1350, section 1, printed page 2 (PDF page 2): battery life about 250 hours.
  3. ↑ 3.0 3.1 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 9 "RAM card", printed page 12 (PDF page 12).
  5. ↑ 5.0 5.1 Sharp, Service Manual, PC-1350, section 6 "Cautions in using the RAM card option", printed pages 3 to 4 (PDF pages 3 to 4).
  6. ↑ 6.0 6.1 6.2 Sharp, Service Manual, PC-1350, section 11 "Parts and signal layout chart (main PWB)", printed pages 17 to 18 (PDF pages 17 to 18), including the jumper and subsidiary board circuit description.
  7. ↑ Sharp Corporation, Service Manual, Model PC-1360, August 1986, section 2 "Introduction", printed page 1 (PDF page 1). Hosted as File:Sharp PC-1360 Service Manual.pdf.
  8. ↑ Sharp, Service Manual, PC-1350, section 10 "Circuit diagram (1)", printed page 13 (PDF page 13).
  9. ↑ Sharp, Service Manual, PC-1350, section 3 "Block diagram", printed page 2 (PDF page 2), and the main board layout (PDF page 17).
  10. ↑ Sharp Corporation, Service Manual, PC-1350, code 00ZPC1350SM/E, September 1984, section 1 "Specifications", printed page 1 (PDF page 1): CMOS 8-bit CPU. Hosted as File:Sharp PC-1350 Service Manual.pdf.


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