I'll check the p/s, but since everything else works correctly, I suspect dirty key contacts and a poor debouncing circuit. Pressing (for example) the "2" key, sometimes it outputs "22", sometimes "2v"... the debounce circuit should take care of the first, and the second has falsely set bits (0x32 vs 0x76). Some of the other keys have either or both errors too - will have to log the errors associated with each key and see if I can find it in the logic.
On 10/5/26 23:27, Richard Loken wrote: > I did elecctronic maintenance in a data centre which included working with a > small number of ADM-3As in the early 1980s. > > I do not recall any complaints about key bounce and I know darn well I would > have heard. Those would likely be mechanical key switches so they may have > oxidised over their long career (but all 58 keys? That does not seem > likely.) Cleaning the contacts with a aerosol contact cleaner may be > possible or it may be possible to take them apart and clean them. > > After 40 or more years on the job, some of the capacitors may be failing - > that is the most common time related component failure . You might look > hard at the schematic focusing especially on electroytic capacitors. If the > power supply becomes noisy due to sagging filter capacitors or the bypass > capacitors are failing and no longer cleaning up the noise on the power > busses then that might contribute to your problem. When diagnosing an > electronic problem, you are wise to start by being suspicious of the power > supply and the power distribution busses. As far as I recall, the ADM3A > would be mostly SSI TTL circuitry and those ICs would require proper noise > suppression. > > The only problem I distinctly recall with an ADM3A was when some academic > spilled rum and coke into the keyboard. I can't recall if I ever fixed it, > I suspect that I scrapped it. > -- > Richard Loken VE6BSV : "...underneath those tuques we wear, > Athabasca, Alberta Canada : our heads are naked!" > ** [email protected] ** : - Arthur Black
