TMS9918A and BIOS 1.6 — for the COB, DEV, KIM, VCS, PicoCalc and ACEs still on the original video card editionCurrent docs →
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When something's wrong ​

Symptom first. Find yours below.

Nothing on the screen at all ​

Work through these in order:

  1. Is the power light on? No light means no 5 V. Check the supply is center-positive and actually delivering 5 V.
  2. Is the monitor on the right input? VGA monitors are cheerfully silent about being on the wrong channel.
  3. Try the serial port. If you have a USB-to-serial adapter, plug it in, open a terminal at 19200 8-N-1, and press reset. If the splash appears there, the computer is fine and the problem is the video path — cable, monitor, or the video module not seated.
  4. Press reset and listen. A beep means the machine got as far as booting.

If there is genuinely nothing — no picture, no beep, no serial output — the machine may have stopped before the splash because it couldn't find any console. Get a serial cable on it; that's the fastest way to find out what it thinks is going on.

No sound ​

  • Is the RCA lead going to something powered? The ACE puts out line level, not enough to drive a bare speaker.
  • Have you set the volume? VOL 15 at the prompt, then SOUND 1, 440, 50. You should get a beep.
  • If the startup beep is missing too, the sound chip isn't being seen — check it's seated properly in its socket, and the right way around.

No beep at startup, but everything else works ​

Same cause as above, and it's harmless: the machine skips the beep when it can't find a sound chip rather than complaining about it. Everything else works normally.

The memory card isn't found ​

DIR says ?NO DEVICE ERROR instead of listing files.

  • Reseat the card. It should click in without force.
  • Try a different card. Very large and very new CF cards sometimes don't support the 8-bit True IDE mode the ACE uses; anything from about 128 MB to 8 GB is a safe bet.
  • Check the CF adapter board is fully seated on the Storage header.

If DIR lists nothing but doesn't error, the card is fine and just empty — FORMAT it and you're away. See Storage.

Keys repeating, or keys getting missed ​

Press reset first: the keyboard controller sets itself up at power-on and very occasionally gets it wrong, and a reset makes it start over. Your program survives, so this costs you nothing.

If one particular key is unreliable, it's the switch rather than the computer — mechanical switches can be cleaned or replaced.

If you're using a PS/2 keyboard in place of the built-in one, try a different keyboard: some USB keyboards with passive PS/2 adapters are only half-hearted about supporting it.

A program won't stop ​

Press Esc. If that doesn't do it — because the program is stuck in machine code rather than BASIC — press reset. Your BASIC program is still in memory afterwards.

?SYNTAX ERROR ​

BASIC didn't understand the line. Nine times out of ten it's a typo:

PRIMT "HI"

?SYNTAX ERROR
OK

The other time, it's a keyword that doesn't exist in this BASIC. LIST and look at the line carefully.

Asking the machine what it found ​

One command tells you what the ACE found when it looked itself over at startup. Type MEM:

MEM
 30718 BYTES FREE  HW=$FF
DISK 0

OK

HW=$FF is a full house — everything present and accounted for. Anything less means one of the pieces wasn't found, and the number tells you which:

Reading the HW number

It's a hexadecimal number, and each bit stands for one part of the machine. Add up the values for everything that's there:

ValuePart
$80Video Card / VGA Card
$40Sound Card
$20GPIO Card / Input Board
$10Serial Card
$08Storage Card
$04RTC Card
$02RAM Card
$01RAM Card

So HW=$7F is everything except video — which is exactly what you'd expect on a machine being driven over a serial cable with no monitor attached. And HW=$FF is everything.

Still stuck ​

The hardware itself — schematics, board revisions, bill of materials — is all in the 6502-ACE repository. If you're chasing something at the board level, that's where to look.

Written for BIOS v1.6. Released under the MIT License.