ADM-3A Wonky Until Warm

Sounds like the sort of issue you could track down by a can of freezer spray (or inverted can of air duster)

Check for bulging caps. they are failing, and work best at a bit higher temperature.

A can of freeze-it spray, a plastic/otherwise completely insulated poking device, and a very old soldered joint/failed component in the vertical deflection section. Including inductors that may not quite be making contact between the enamelled copper wire and its pins, capacitors/resistors with hairline cracks in.

Once it's warmed up and "just about" working, cautiously poke, tap, or zap with cold-spray and see if it fails.

Any sight/sound of arcing/sparking when it goes from working to not? If so, observe it in low light conditions and keep your eyes open. Better still, aim a camera at the board to see where it sparked, in case you miss it.

is still fine as long as I don't let the ADM cool off first. Does anyone know what the problem might be? What to look for?

I would also check for bad capacitors. Instead of the freeze spray, try heat. I have a hot air rework station and the heat wand has a very small nozzle where I can heat a small portion at a time. The heated capacitors usually make the problem go away very quickly when the device is first turned on.

In a device of that age, start by replacing all larger caps (physical size of 12mm/.5" in diameter and larger) and re-solder all largish pins in the circuit boards (inductors, transformers, connectors).

When there still is a problem after that you can use heat/cold to hunt for a smaller failed component.

squashed and the top line is mangled. After five minutes or so the display looks OK but is a little jumpy. After a few more minutes, the display is r ock-solid and stays that way until the next time I turn it on cold.

Either some of the video adjustments are temperature-sensitive (not impossi ble, but unlikely) or you have a mechanical stress issue; maybe cracked solder j oints, maybe a dirty connector.

If you know how to safe the CRT, you can open it up and exercise the connec tors, look at solder joints (especially at heavty wires or connector pins) and ma ybe tap with a chopstick at various points DISTANT FROM the anode wire while power is on.

If you care about its function, do be gentle with the CRT; those are irrepl aceable.

The freezy spray comments are just going to waste your money. You are not having intermittent problems when the unit heats up. Grab a heat gun and hit the capacitors. If you have a kit of spares, just start to replace them, or solder tack new ones across the bad ones and see which one fixes the issue. I used to have an adm-5a, a very similar unit.

Here's a full manual, schematics start on page 57

It's a great terminal, except for how that damn keyboard feels.

I agree with the others, caps are usually the culprit. But don't waste time tracking down the individual component - that's for modern hardware with the occasional failed cap. Old hardware like this should be completely 're-capped'. That is, replace ALL the caps. Why? because they degrade over time (especially electrolytics) and after a few decades almost all of them will be due to fail soon. So just do it now and get it over with.

-John G.

Ohh, that's the exact signature of a bad elecrolytic cap in the vertical drive circuit of the monitor. Many monitors of that vintage had bipolar electrolytic caps in the vertical circuit. These may be hard to source, but you should be able to find a suitable replacement.

Jon

squashed and the top line is mangled. After five minutes or so the display looks OK but is a little jumpy. After a few more minutes, the display is r ock-solid and stays that way until the next time I turn it on cold. If I tu rn it off back on, the display is still fine as long as I don't let the ADM cool off first. Does anyone know what the problem might be? What to look f or?

After all the remedies You may also check the tube base and its connectors