I've actually been either busy with work, real life or fixing computers and have forgotten to post about it.
So I just thought I'd share a little fix I've just finished in case it helps some of you out.
On the desk I have a BBC B Issue 7 with extra rom, ram etc etc. Anyway, it had a keyboard fault, essentially the only keys that would work were on the right hand side of the keyboard and even then by work I mean they would print characters on the screen, just not the correct ones.
The Keyboard ribbon was checked as were the header pins, which were a little crusty to begin with. There are four chips on The BBC B keyboard, the two middle ones are the ones primarily to do with the keyboard. A 7445N which is a BCD to decimal decoder, this one is responsible for detecting the individual key presses and then transmits it over to the 74LS163 which then decodes the data and resends it off again in a format that the 6522 VIA chips can understand. (or that's how I think it works
)With the scope I verified that the 7445 was receiving the correct keypresses but there seemed to be nothing b being sent out to the 74LS163. It turned out that 3 of the 4 inputs on the 163 were not working and pulling the signal low for some reason.
I removed the very rusty 163 and upon trying to put it into the TL866 to test a couple of its legs fell off.... OOoops, I guess we know that's dead then
Replaced the 74LS163 and put it all back together and whoop whoop I now have. working BBC B.
