View Full Version : BBC B needs diagnosis

April 3rd, 2011, 12:05 PM
Hi, I have come across a BBC-B with these symptoms

CAPS LOCK key stays on

Keys don't do what they are supposed to, Either the wrong thing or nothing

Audible white noise

The boot display looks as it should

Might a good clean and re-seating whatever I can help any?

Thankyou :)

April 3rd, 2011, 04:05 PM
The stuck CAPS LOCK LED suggests the keyboard scanning is FUBAR, or the keyboard itself is in need of some TLC. The white noise is normal if the volume pot has been turned up to eleven, unless there's something wrong with the SN76489 sound generator chip...

As I recall, keyboard scanning is done with one of the 6522 VIAs (probably the System VIA). I'd start by swapping the User and System VIAs. That'll prove if you have a dead VIA (or not).

Next -- check for stuck or dirty switches on the keyboard (BBC series machines are real swines for this). Also check the motherboard links (jumpers) are set correctly.

If your machine was from the BBC Master series (e.g. Master 128, 512, ...) I'd suggest replacing the CMOS battery, resetting the config (DEL-power-on or R-power-on -- one is for RISC OS, the other is for BBC MOS, I can't remember which is which) then configure it using the settings from the Welcome Guide.

Also, I think R J Sprowson (Sprow) has some troubleshooting hints on his website. I'm not 100% sure if they're Master-specific or cover the B as well...

April 4th, 2011, 02:01 PM
dodgy 6522 sounds likely, I'll give it a go

Thanks :D

April 7th, 2011, 12:14 PM
Theres a sideways expansion module installed incorrectly ,Pins bent ,Will test now I've re-seated it,
Now it says all stuff about mode 7 , default printer and some other stuff.
Keyboard is the same but still haven't tried the via.

April 7th, 2011, 01:51 PM
2nd re-seat of the module I noticed the keyboard connector was wonky (not sure If I did that myself) but the keys are all correct now.

Should I just remove the sideways module ,I'm not sure if the pins are still bent on it as I cant see them underneath!

Its a big old thing with lots of roms in it. languages and stuff.