Jump to content

Sharp PC-1251 General Maintenance

From RetroTechCollection
Sharp PC-1251 in a CE-125 printer and microcassette recorder
A PC-1251 docked in a CE-125 printer and microcassette recorder (photo: Mspecht, CC0)

Routine care of the Sharp PC-1251. The PC-1251 runs at 6 V from two CR2032 lithium cells and has no mains voltage inside, so maintenance is about the cells, the reset procedures, cleaning, the contrast setting and the CE-125 if one is used.[1][2] Sharp's service manual covers the PC-1250 and PC-1251 together, and the same steps apply to a PC-1250.[3]

Cells

[edit | edit source]
PC-1251 cells (Sharp)[1][4]
Item Detail
Type Two CR-2032 lithium cells, in series for 6.0 V
Life About 300 hours of use at 0.03 W
When to replace The display stays dim and hard to read from the front even with the contrast control turned fully anticlockwise
Rules Replace both cells together; do not mix a new cell with a used one

Changing the cells clears the memory: Sharp lists a battery change, like the ALL RESET button, among the events that erase variables.[5] Save programs and data to tape through the CE-125 before replacing the cells, as the manual advises.[4]

Replacing the cells

[edit | edit source]

Sharp's procedure:[4]

  1. Set the power slide switch to OFF.
  2. Remove the screws from the back cover with a small screwdriver.
  3. Slide the cell cover off in the direction of the arrow.
  4. Replace both cells.
  5. Slide the cell cover back.
  6. Hook the claws of the back cover into the slits in the case.
  7. Push the back cover in slightly while refitting the screws.
  8. Switch on and press the RESET button to clear the computer. The prompt > should appear. If the display is blank or shows any other symbol, take the cells out, refit them and check again.

Sharp's service manual warns that a cell that is not seated properly, or makes poor contact, can cause a flickering display or damage other parts.[6] Check the cell terminals for corrosion and tension whenever the cover is off.

Storage and leakage

[edit | edit source]

Remove the cells when the computer will not be used for a long time. Sharp's manual says a dead cell left in the computer can leak and damage it, and should be removed promptly.[7][4] For cleaning up corrosion, see Battery Explosion, Capacitor or Corrosion Damage.

Reset

[edit | edit source]

The RESET button is on the back and is pressed with a ball-point pen, not a pencil or a needle. There are two levels:[8]

  • Hold down any key and press RESET. This resets the computer and keeps all programs, variables and reserve memory.
  • Press RESET without holding a key. This clears the program, the data and all reserved contents. Use it only when the first method does not bring the keys back.

Cleaning and handling

[edit | edit source]

Sharp's maintenance notes for the PC-1251:[7]

  • Handle the computer carefully: the LCD is glass.
  • Keep it away from extreme temperature changes, moisture and dust, and out of vehicles parked in direct sun.
  • Clean it with a soft, dry cloth only. Do not use solvents, water or wet cloths.
  • Strong static electricity or external noise can make it hang with all keys dead. Hold any key and press RESET.

Contrast

[edit | edit source]

The contrast control is on the right-hand side of the computer. Turn it in the direction of the arrow for a clearer display and the other way for a dimmer one, and set it so that the display is easy to read.[9] Inside, it is a 20 kΩ variable resistor that sets the LCD drive voltage VDIS.[2] Sharp's service check for display quality is that the display does not blur when viewed at 30° and shows no irregular contrast at 10°.[6]

CE-125 printer and microcassette recorder

[edit | edit source]
  • Switch both units off before docking the PC-1251. If the computer is on, it may hang; clear it with the ALL RESET button. Remove the protective pin cover from the left of the computer and fit it to the bottom of the CE-125.[10]
  • The CE-125 runs from a rechargeable Ni-Cd battery. Recharge it when the low battery indicator lights; a full charge takes about 15 hours. A CE-125 that has been stored will need charging before use.[10]
  • When the PC-1251's cells run low with the CE-125 attached, the CE-125 supplies the computer.[10]
  • Clean the CE-125's tape heads periodically with a standard head cleaning kit.[11]

Inside the case

[edit | edit source]
  • The memory module board is held by screws whose holes have some play. Sharp warns that a board refitted slightly out of alignment can cause improper operation; reseat it and press the ALL RESET switch before use.[6]
  • Sharp's service tool chassis (LCHSS1134CCZZ) is smaller than the production chassis that sits on top of the main board, and makes the board easier to work on. Refit the original chassis when the repair is finished.[6]
  • The logic is CMOS. Use an anti-static strap.[1]

Capacitors

[edit | edit source]

The PC-1251 has two small polarised capacitors: 3.3 µF 10 V across the VGG supply and 1 µF 6.3 V in the LCD bias circuit.[2][12] See Sharp PC-1251 Capacitor Replacement Guide.

Preventive maintenance checklist

[edit | edit source]
  1. Save programs to tape before any cell work.
  2. Remove the cells for storage and inspect the terminals.
  3. Wipe the case with a soft, dry cloth.
  4. Check that the contrast control gives a clear display with fresh cells.
  5. Check every key and the ON/BRK key.
  6. If a CE-125 is used, charge it and clean its tape heads.
[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 Sharp, PC-1251 instruction manual, appendix G "Specifications", printed page 173 (PDF page 175): 8-bit CMOS CPU; 6.0 V DC lithium cells, type CR-2032; 0.03 W, about 300 hours. Hosted as File:Sharp PC-1251 Instruction Manual.pdf.
  2. ↑ 2.0 2.1 2.2 Sharp, Service Manual, Model PC-1251, PC-1250, section 7 "Circuit diagram", printed page 10 (PDF page 12): CR2032 × 2 in series, VR 20 kΩ on VDIS, 3.3 µF, 1 µF.
  3. ↑ Sharp Corporation, Service Manual, Model PC-1251, PC-1250, December 1982, sections 1 and 2 (PDF pages 1 to 2). Hosted as File:Sharp PC-1251 Service Manual.pdf.
  4. ↑ 4.0 4.1 4.2 4.3 Sharp, PC-1251 instruction manual, chapter 2, "Cell replacement" and "Installing the cells", printed pages 13 to 15 (PDF pages 15 to 17).
  5. ↑ Sharp, PC-1251 instruction manual, chapter 3, printed page 26 (PDF page 28): variables are lost when the ALL RESET button is used or the batteries are changed.
  6. ↑ 6.0 6.1 6.2 6.3 Sharp, Service Manual, Model PC-1251, PC-1250, section 6 "Service precautions", printed page 9 (PDF page 10).
  7. ↑ 7.0 7.1 Sharp, PC-1251 instruction manual, "Maintenance", printed page 154 (PDF page 156).
  8. ↑ Sharp, PC-1251 instruction manual, chapter 2, "ALL RESET", printed page 12 (PDF page 14).
  9. ↑ Sharp, PC-1251 instruction manual, chapter 2, "Contrast control", printed page 13 (PDF page 15).
  10. ↑ 10.0 10.1 10.2 Sharp, PC-1251 instruction manual, chapter 7, the CE-125 (PDF pages 54 to 57).
  11. ↑ Sharp, PC-1251 instruction manual, chapter 7, CE-125 care (PDF page 64).
  12. ↑ Sharp, Service Manual, Model PC-1251, PC-1250, section 9 "Parts list" (PDF page 18): RC-SZ1021CCZZ 3.3 µF 10 V; RC-SZ1007CCZZ 1 µF 6.3 V.


Retrieved from "https://retrotechwiki.com/index.php?title=Sharp_PC-1251_General_Maintenance&oldid=28776"