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Coleco Adam

Coleco's 8-bit computer (1983), an expansion of the ColecoVision: a Z80, a TMS9928A VDP, SN76489 sound, a high-speed digital cassette drive (Digital Data Pack) and a daisy-wheel printer… that contains the whole system's power supply. Famously fragile; a delicate repair.

Coleco Adam

Coleco Adam — photo by Akbkuku, CC BY 4.0 (Wikimedia Commons).

Identification

  • CPU: Z80A; Video: TMS9928A (as MSX/ColecoVision); Sound: SN76489.
  • Media: Digital Data Pack (proprietary fast cassette), ColecoVision cartridge, optional floppy.
  • PSU inside the printer: without the printer connected, the machine won't start.

Clocks & frequencies ✅

Component Frequency Role / scope
Zilog Z80 3,58 MHz CPU principal — c'est la fréquence du color burst NTSC, pas les 4 MHz dont le Z80 est capable
Motorola 6801 — second processeur, dit « Master 6801 » : périphériques et extension mémoire/ROM

The Z80 deliberately runs below its maximum (3.58 MHz instead of 4 MHz) to lock onto the NTSC colour burst. This is a dual-processor machine: the 6801 handles peripherals, which is why a drive or keyboard fault can leave the Z80 perfectly healthy.

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)

The PSU is in the printer

The system's mains supply is built into the daisy-wheel printer. A dead printer = the whole Adam is dead. Many opt for a modern replacement PSU (community mods) to be free of the printer.

  • "Power-on erase bug": a Data Pack left in the drive at power-on could be wiped by an electromagnetic pulse from switching on → remove the tape before powering up.
  • Recap (printer/PSU + board) → Recap.
  • Digital Data Pack: belt / head / pad → clean, replace; alignment is delicate.
  • VDP / RAM: substitution (VDP shared with MSX/ColecoVision).
  • Cartridge / keyboard contacts: clean.

Procedure — a dead computer, step by step ✅

The power supply is in the printer

Which means the machine will not start without it — and that a fault that looks like a dead computer may be in a part you have not even plugged in.

What this adds

Ordered for a home computer: what kills these is its power supply, its battery, its capacitors, its socketed RAM and its keyboard — roughly in that order, and well before the CPU. → PCB diagnosis

1. The power supply — measured before it is plugged in. This is the one step not to swap around. On a machine of this age a supply does not simply stop: a 5 V regulator that fails high puts 7, 9, 12 V onto the bus and takes the RAM and the custom chips with it. Measure every rail off the machine, under a dummy load if you can, and only then plug it in.

2. The battery, if it has one. Any RTC or backup cell soldered to a board is a future leak. If yours has one and it has never been changed, take it out before it takes the tracks with it. → Backup batteries

3. Capacitors. Recap is the default on these machines, not a last resort — and on the supply first, since that is what protects everything else. → Recap

4. RAM, on its sockets. These machines were built to be repaired: the RAM, and often the logic, sit in sockets. Reseat everything first — thirty years of oxide is a classic no-boot. Then swap chips: a bad RAM chip usually gives a repeatable pattern of garbage or a screen frozen at a fixed character.

5. The keyboard. A console does not have one; a computer's is a wear part. A membrane keyboard fails as whole dead rows or columns — that is the membrane, not the machine. A mechanical one wants its contacts cleaning, not replacing. Check this page: the failure mode is often documented per model.

6. Storage — tape or disk. Both often come down to the same things: a dirty head, and for tape the azimuth and a belt turned to tar. ⚠️ On the floppy side, check whether the mechanism actually has a belt before looking for one: many do, but some drives are direct drive, and hunting a belt that isn't there means stripping a drive for nothing. A machine that boots but loads nothing is a drive fault, not a logic fault — do not go looking on the board for it.

7. Video output. RF, composite, RGB or a dedicated monitor, depending on the machine (see Identification). Test with something else before you conclude: a period modulator and a modern TV disagree far more often than either is broken.

8. Still nothing. Now the logic: rails on the board, reset, clock, bus. → PCB diagnosis

Common faults

Symptom Likely cause Lead
Won't start dead printer/PSU Repair printer / modern PSU
Data Pack wiped/unreadable power-on pulse / mechanism Remove tape before power-on; service drive
Partial picture/sound VDP / SN76489 / RAM Substitute
Instability caps Recap

Modernisation & mods — what to buy, how

PSU in the printer + power-on erase

The original supply is in the printer → an external regulated replacement brick (the #1 mod, very common) runs the Adam without the printer and kills the "dead printer = everything dead" failure. ⚠️ Remove the tape (Data Pack) before power-on: power-up erases an inserted tape.

Modern storage - SD-card drive emulators 🟡 (replace the fragile Digital Data Packs) and modern disk boards on AdamNet → images loaded from SD, no more aligning tapes. - Memory expansion (64 KB and up) 🟡 to widen software compatibility.

Video - TMS9928A VDP → composite output; image-quality mods 🟡 as on MSX/ColecoVision.

Reliability: recap 🟠; clean contacts.

⚠️ Do not host ROMs/games — method only.

Archived manufacturer documentation ✅

  • Coleco Adam — documentation — PDF

See also

Sources & attribution

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.