TRS-80 PC-6 General Maintenance
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The TRS-80 PC-6 runs from two CR2032 lithium cells and keeps its memory on a separate CR1220 cell, so most routine care concerns the three cells. The other parts that need attention on a PC-6 today are the clamshell's hinges and front latch, the membrane keyboard in the lid and the heat-sealed connections between the boards and to the LCD. Tandy's service manual is the source below unless another is given.[1]
Cells
[edit | edit source]The three cells
[edit | edit source]| Cell | Use | Tandy's rated life |
|---|---|---|
| 2 × CR2032 | Main supply | About 85 hours of continuous program execution; about 200 hours of continuous display; about 5.5 months at one hour of mixed use a day |
| 1 × CR1220 | Memory backup | About two years with the main cells fitted |
Kaiser notes that the PC-5 and PC-6 are the only Tandy pocket computers whose memory survives while the main cells are out, because the backup cell keeps the RAM.[2] To keep programs, change the main cells and the backup cell at different times, never both together, and save anything important to tape first.
Changing them
[edit | edit source]The Floodgap archive, the source of the service manual, has no PC-6 owner's manual, so Tandy's own cell-changing procedure is not available. The parts list gives a 1.7 × 5 mm pan-head machine screw for the CR2032 cells and a 2 × 5 mm flat-head tapping screw for the CR1220, with separate holders for each (A35802-1 and A35803-1).[1] Switch off first, note which way up each cell sits before removing it, and fit the new cell the same way round. After changing the cells, switch on and check that Ready P0 appears.
Contacts
[edit | edit source]Tandy's fault table lists poor battery contact as a cause of a blank display. The remedy it gives is to clean the cell and its contact spring and to lift the battery spring.[1] If a cell has leaked, follow Battery Explosion, Capacitor or Corrosion Damage for the clean-up.
The springs for the CR2032 pair carry the same Casio part numbers as the TRS-80 PC-4's battery springs: 63297621, 63297630 and 63297640, with insulation seal A45154-1 (63297660) in both computers.[1][3]
| Item | Description | RS part no. | Manufacturer part no. |
|---|---|---|---|
| 10 | Holder, Battery, for CR1220, A35803-1 | AB-0623 | 63349650 |
| – | Spring, Battery contact (−), for CR1220, A35801-1 | AB-0621 | 63349890 |
| – | Spring, Battery contact (+), for CR1220, A35800-1 | AB-0622 | 63349900 |
| 12 | Holder, Battery, for CR2032, A35802-1 | B-0058 | 63349640 |
| – | Spring, Battery contact (−), for CR2032 | ARB-7639 | 63297621 |
| – | Spring, Battery contact (+, −), for CR2032 | ARB-7640 | 63297630 |
| – | Spring, Battery contact (+), for CR2032 | ARB-7641 | 63297640 |
| 1 | LCD, CA51-TS | AL-1020 | 33310552 |
| 3 | Seal, Heat, T-07-12 (LCD to board) | AHC-0107 | 56005846 |
| 4 | Seal, Heat, PCB-G707-1 to PCB-G707-2, CAX-12-3 | AHC-0348 | 56006320 |
| – | Sheet, Keyboard, C3473-5 | AHC-0346 | 82636721 |
| – | Assembly, Film, keyboard, C3769A-1 | AK-0518 | 63471021 |
| – | Film, Keyboard, C3768-1 | AHC-0347 | 63471030 |
Hinges and latch
[edit | edit source]Kaiser's new-old-stock PC-6 began to split at the hinges after only a few openings, and he reports that most PC-5 and PC-6 units on the second-hand market have broken hinges or latches, with no easy repair. He recommends pressing on the hinge covers with a finger as you open the lid, or taping over them for reinforcement.[2]
For a broken front latch, a 3D-printed replacement for the PC-5, PC-6, FX-780P and FX-790P was published on Thingiverse in 2022 under a CC BY 4.0 licence. Its instructions are to trim the broken latch so that it fits inside a pocket in the printed part, test the fit, and glue it in place.[4]
The service manual's own instruction for opening the upper case is to insert tweezers into the back of the upper case and move them gently in the direction of the arrow in its drawing.[1]
Keyboard and display
[edit | edit source]- Tandy's fault table gives poor key contact as the first cause of a dead key; clean the contact pads on the board and the key contact rubber.[1]
- The letter keys are a membrane panel in the lid. Kaiser describes it as mushy and says it flexes under use.[2]
- The contrast control VR1 is a 20 kΩ variable resistor (EVL-AHAA00B24) at the bottom of the LCD voltage divider.[1]
- A blank display or missing segments can come from a peeled or broken heat seal; see TRS-80 PC-6 Troubleshooting Guide.
Options and the RAM pack
[edit | edit source]Switch the computer off before connecting the printer or cassette interface.[1] The 26-3674 RAM pack is screwed into place.[2]
Opening the case
[edit | edit source]The service manual's disassembly procedure:[1]
- Remove the three screws (19) from the lower case.
- Lift up the lower cases (18) and (7).
- Remove the nine screws (13), one screw (15) and one screw (16) from the PCB holders (11) and (5).
- Remove the PCB holder and the two cells.
The two boards, PCB-G707-1 and PCB-G707-2, are joined by the heat seal CAX-12-3, so lift them carefully and do not fold or pull on it.[1] The HD61747 processors are CMOS parts; work on an earthed mat.[2]
Tools
[edit | edit source]- Small cross-head screwdrivers for the 1.7 mm and 2 mm screws
- Fresh CR2032 and CR1220 cells
- Tweezers for the upper case
- An earthing strap or mat when the case is open
See also Recommended Tools.
Related pages
[edit | edit source]- TRS-80 PC-6
- TRS-80 PC-6 Troubleshooting Guide
- TRS-80 PC-6 Capacitor Replacement Guide
- TRS-80 PC-6 Documentation
- TRS-80 PC-5 General Maintenance – the same case with 4 KB of memory
References
[edit | edit source]- ↑ 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. Specifications and how to open the upper case p. 3; power supply p. 7; troubleshooting guide p. 10; operation check notes p. 14; parts lists pp. 20–22; exploded view and disassembly p. 23; schematic p. 24.
- ↑ 2.0 2.1 2.2 2.3 2.4 Cameron Kaiser, "Tandy Radio Shack Pocket Computer PC-4 and Tandy Pocket Scientific Computer PC-5, PC-6, PC-7", Floodgap Retrobits, Tandy! Pocket! Mania!. Retrieved 2026-10-21. PC-5 and PC-6 section: the memory backup battery; the membrane keyboard; hinges splitting and latches cracking, and pressing on the hinge covers or taping them; the 26-3674 RAM pack screwed into place.
- ↑ Radio Shack, Service Manual: TRS-80 PC-4 Pocket Computer and Cassette Interface. Hosted as File:Radio Shack TRS-80 PC-4 Pocket Computer and Cassette Interface Service Manual (26-3650).pdf. Parts list p. 27: Spring, Battery A, B and C (63297621, 63297630, 63297640) and Plate, Battery Insulation G272 A45154-1 (63297660).
- ↑ Thingiverse thing 5409498, "Tandy PC-5, PC-6 or Casio FX-780P, FX-790P latch", 12 June 2022, CC BY 4.0. Archived copy at the Internet Archive, thingiverse-5409498. Retrieved 2026-10-21. Description: a replacement latch for the Tandy PC-5/PC-6 (Casio FX-780P/FX-790P); trim the broken latch to fit inside the pocket of the printed replacement, test the fit and glue it in place.