Tandy TRS-80 Color Computer (CoCo)¶
Tandy/Radio Shack's 6809 line (1980) — an elegant architecture (the 6809 is one of the finest 8-bits), with optional OS-9 multitasking. Three generations: CoCo 1/2 (VDG MC6847) and CoCo 3 (1986, GIME chip, 128/512 KB, 640×192). Standard 8-bit repair: recap, video, RAM.
TRS-80 Color Computer — photo by Bilby, CC BY 3.0 (Wikimedia Commons).
Identification¶
| Model | Year | Video | Note |
|---|---|---|---|
| CoCo 1 | 1980 | MC6847 (VDG) | "chiclet" case then full keyboard |
| CoCo 2 | 1983 | MC6847(T1) | compact, many revisions |
| CoCo 3 | 1986 | GIME | 128/512 KB, 640 px, extended palette |
CPU: Motorola 6809 (6809E); Sound 6-bit DAC; cartridge (Program Pak), cassette, floppy (FD-500), serial ports.
Clocks & frequencies ✅¶
| Component | Frequency | Role / scope |
|---|---|---|
| Motorola 6809 | 0,895 MHz | CPU — CoCo 1 et CoCo 2 |
| Quartz | 14,31818 MHz | (NTSC) — quatre fois la fréquence du color burst |
| VDG | 3,579545 MHz | (NTSC) — le quartz divisé par 4 alimente le générateur d'affichage |
Everything derives from a single 14.31818 MHz crystal: divided by 4 it gives the VDG's 3.579545 MHz. That is the measurement point to reach for first on a dead machine.
Why this matters in repair
A clock that is missing or off-value on a frequency counter points straight at the crystal, its divider chain or the component it feeds — the fastest starting point on a machine that will not boot. Source: Wikipedia (CC-BY-SA).
Repair (technician)¶
- Recap (PSU + board) → Recap.
- Video: RF/composite (CoCo 1/2) or RGBA (CoCo 3) output → composite/RGB mods are common.
- Heat (CoCo 1/2): the MC6847 and regulators run hot → heatsinks, check joints.
- RAM: failing DRAM → substitution / test.
- Cartridge contacts: clean.
- CoCo 3: the GIME chip is the weak point (unobtainable new) → handle with care.
Common faults¶
| Symptom | Likely cause | Lead |
|---|---|---|
| No / garbled picture | video (VDG/GIME) / RF | Mods, substitute |
| Crashes when hot | regulator overheating | Heatsinks |
| Memory corruption | DRAM | Test / replace |
| Instability | caps | Recap |
Modernisation & mods — what to buy, how¶
CoCo 1/2 run hot; the GIME is unobtainable
The CoCo 1/2 run hot → heatsinks on the MC6847 and regulators, test DRAM. Recap. The GIME (CoCo 3) is unobtainable new → handle it with care (no spare chip).
Modern storage
- CoCoSDC 🟢: an SD-card floppy controller → mounts .dsk images, replaces the FD-500 (in the Program Pak).
- DriveWire 🟢: a serial-to-PC cable = virtual disks (shared with the Dragon).
- Multi-game cartridges / flashcarts 🟢 on the Program Pak.
Video - CoCo 1/2: RF output → widespread composite mod 🟡; CoCo 3: RGBA output 🟢 → RGB2HDMI (Pi) or an upscaler for crisp HDMI.
Expansion - RAM upgrade 🟡 (512 KB, even 2 MB via Disto boards); accelerators/clocks (Cloud-9 et al.) 🟡.
⚠️ Do not host ROMs/games — method only.
See also¶
- Atari 8-bit (same US era) · Recap.
Sources & attribution¶
- Photo TRS-80 Color Computer — Bilby, CC BY 3.0, Wikimedia Commons — https://commons.wikimedia.org/wiki/File:TRS-80_Color_Computer_1_4x3.jpg
- Wikipedia — TRS-80 Color Computer (6809, MC6847, GIME) — CC-BY-SA — https://en.wikipedia.org/wiki/TRS-80_Color_Computer
- Established CoCo community knowledge (VDG heat, GIME) — synthesis.
Review & corrections
How this space is used
Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.
Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.