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TRS-80 PC-6 Capacitor Replacement Guide

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Tandy PC-6 power supply and memory backup schematic (service manual 26-3672)
Supply section of the PC-6 main block schematic: C13 across the main cells after D3, C12 beside the CR1220 backup cell, and C11 at the 12-pin option connector

The TRS-80 PC-6 has three electrolytic capacitors, C11, C12 and C13, all in the supply. Tandy's service manual lists them with values, ratings and part numbers; every other capacitor on the boards is a chip ceramic.[1] Tandy's fault table for the PC-6 names cells, battery contacts, heat seals, the LCD, the processors and key contacts, and no capacitor.[1] Check those first; see the TRS-80 PC-6 Troubleshooting Guide.

Capacitor list

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PC-6 capacitors (service manual p. 20, positions from the schematic p. 24)
Ref. Type Value Rating Part RS part no. Position
C11 Electrolytic 22 µF ±20% 10 V CE04C-1A220MS7 CE-226MCBA At the 12-pin option connector, between GND and VDD1 after R12 (220 Ω)
C12 Electrolytic 22 µF ±20% 10 V CE04C-1A220MS7 CE-226MCBA In the memory backup circuit beside the CR1220 cell, D2 and R22
C13 Electrolytic 100 µF ±20% 10 V CE04C-1A101MS CE-107MCBA Across the main supply from the two CR2032 cells, after diode D3
C1–C4 Chip ceramic 100 pF ±5% 25 V CM21CH101J25V ACF-1466 Not normally replaced
C5–C10 Chip ceramic 0.1 µF +100% 15 V CM21YV104P15V ACF-7347 Not normally replaced

The manufacturer's part numbers in the parts list are 28047223 for C11 and C12 and 28041047 for C13.[1]

Before you start

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  • The disassembly procedure takes out the two main cells. Save anything in memory to tape first in case the backup cell does not hold it.[1]
  • Note which way round each capacitor sits before removing it; the stripe on an aluminium electrolytic marks the negative lead. The schematic shows the cells' positive terminals on the line marked GND, the same arrangement as on the TRS-80 PC-4, so do not assume the negative lead goes to GND.[1]
  • The two boards are joined by the heat seal CAX-12-3. Do not fold it sharply or pull on it, and keep the soldering iron away from it.[1]

Procedure

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  1. Open the case as the service manual describes: remove the three screws from the lower case, lift off the lower cases, remove the eleven screws from the PCB holders, and lift out the PCB holder and the cells.[1]
  2. Find C11, C12 and C13 using the PCB assembly views on page 19, which carry the component references, and the schematic on page 24.[1]
  3. Record the marking and orientation of each part, then photograph the area.
  4. Remove one capacitor at a time with a temperature-controlled iron and wick or a pump.
  5. Fit 22 µF 10 V parts at C11 and C12 and a 100 µF 10 V part at C13, or the same capacitance at a higher voltage if it fits the space, in the same orientation as the originals.
  6. Reassemble, fit fresh cells and the CR1220, and switch on.

After replacement

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  • The display should show Ready P0.
  • Run the memory check program and the operation check from the service manual; see TRS-80 PC-6 Troubleshooting Guide.[1]
  • If the computer forgets its programs when the main cells are changed, check C12, D2, R22 and the CR1220.[1]

See also Capacitor Failure Symptoms and Recommended Tools.

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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Tandy, Service Manual: Pocket Scientific Computer PC-6, catalogue number 26-3672. Hosted as File:Tandy PC-6 Pocket Scientific Computer Service Manual (26-3672).pdf. Power supply p. 7; troubleshooting guide p. 10; PCB assembly view p. 19; electrical parts list p. 20; disassembly p. 23; main block schematic p. 24.


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