I don't know if my house is haunted or if I should quit this hobby, but I'm facing the Keyboard of Hell on my Apple II Europlus repair.
Or maybe the whole thing is cursed, as it's the 5th thing in a row I repair and it's not yet fully functional.
Anyway ; symptoms are bizarre
- Nearly EACH key I type is immediatly followoed by an underscore (a key that is not on the keyboard by the way)
- If i barely touch the cable, it registers underscores as well (I think it's like the 50Hz noise my fingers carry that make it regsiter that)
- super interstingly, if I keep a key pressed, the key repeats itself with and underscore between each letter
- the cable
- the two DIP sockets
- swapped all the ram and limited it to first 16K just to be sure
to no end. I'm postivie this cable is OK, and the same problem occurs with another cable. The sockets are new. Of course everything has been cleaned (including the small key blades under each key), reseated chips, all 74LS are tested OK, etc. The ROM can be read (it's seems to be a grid of 00 and 80s)
If I remove the keyboard the keys) and just connect the encoder, it also registers underscore if I barely touch the cable.
It does not "by itself" type letters without a keybaord attached. The fact it registers those underscore even if I keep a key pressed down is probably important but I'm not sure what to think of it.
I'm not yet sure of that last part ; but I think it's not always the same keys that are affected, and 80% of they key register an extra underscore, whereas the remaining 20% work fine.
I'm really getting out of options here. The thing seems overly sensitive to god knows what.
I read in an old topic about a debouncing capacitor, does anyone know more about that ?
Is there a schematic of the "ENHANCER" board ?