Troubleshooting a broken M0110A Keyboard?

[dv-]

Anybody have (or know where I can get) wiring diagrams for a Mac Plus Extended keyboard?

I have one that's just a doorstop; other keyboards work fine with the same Plus / cable, but this one does nothing. I'm specifically curious about how to test that big microcontroller. (Would I need, like, an oscilloscope app?)

The contacts grid seems to check out alright, so I think the traces on the board are ok (a few scuffs and scratches but continuity is good.)

I replaced the two barrel caps; the resistors checked out ok, per my multimeter. Resoldered everything else just 'cuz.

I've read that if they're unplugged/plugged back in during operation, or used with an incorrectly wired headset cable, they can very rarely get fried - is there any deeper info on what happens when that occurs?

TIA

 

[Wiggs1979]

I realise this is an old post, but I purchased a M0110A keyboard from a well known auction site and it was basically a doorstop. Like yourself, I tested all the passives and they all checked out okay, indicating it had to be the controller chip. Once you've narrowed it down to that though, I don't think you can really do much more than replace it. I probed it with a logic probe for the clock signals, but it appeared to be dead.

Fortunately, I have an old EPROM programmer that can handle chips like 8748 and it didn't take too much searching to find a ZIP file with the code for the keyboard controller - search for mackbd and you'll probably find it.

With the keyboard being a single-sided Mitsumi PCB, a hot iron with a bit of solder wick made light work of removing the faulty 341-0332, fitted a socket and dropped in a programmed NEC D8748D and I am back in business, a fully working keyboard.



If anyone needs an 8748 programming, I'm happy to help out (I'm UK based). Last I looked, the supplier I bought mine from only had one left, very tempting to pick it up as a spare since I know that supplier is good.

 

[obsolete]

That's awesome! Great fix.