8-bit acorn hardware • Model B keyboard problem

Hi, I just got my first BBC Micro B (issue 4).

Intro

I bought it broken so I could learn about the hardware in this legendary machine while repairing it.
The poor thing was in awful shape: A busted PSU and a severe battery leak from a Watford ROM expansion board which got to the mainboard during the decades.
After fixing PSU, cleaning the motherboard, lengthy troubleshooting, and replacing a dozen non-working chips and corroded sockets (it was fun!), it now passes al tests... apart from the keyboard.

Problem

Many keys did not work, so I de-soldered, cleaned and de-oxy'd all non-working keys. Keyboard worked decently after some (break-in) until yesterday.
Now when I turn it on, three keys don't register keypresses 95% of the time (they are "R", "G", "V"), and when I press any key (working or not), the beeper emits a buzzing sound which was certainly not there last time it worked. It's not static noise, it's more like a low "error sound".
I checked the keyboard PCB traces, and they seem to be working (although very oxidated).

What do you suggest ?
Also, are there modern replacement switches for that keyboard ?

Statistics: Posted by DDT — Mon Dec 30, 2024 8:22 pm

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