Trying to fix a BBC Micro (B)

[dougal]

Hi, non-Amiga question here.

A friend of mine gave me a BBC Micro B, has a rev 7 board. I tried hooking it up, the PSU popped and smoked.

Before & after it popped the speaker constantly beeps - the tone of the beep different almost every time I switch it on.

The CAPS light is stuck on.

Composite or RF gives different displays when switched on. Either grey and jumpy screen or black and jumpy screen etc..

I tried re-seating all the socketed chips.

I tested the voltages: +5V is fine and -5 reads out -4.3v to -4.6v when everything is plugged into the board or else -3.somethingV when all power cables unplugged.

If I remove IC6 (video chip ?) and switch on there is no beeping anymore.

Any ideas ? I've never worked on a Beeb before

 

[trixster]

I’d recommend you join the excellent Stardot forum. The guys on there will have your problems diagnosed and fixed pretty much immediately!

 

[dougal]

Thanks

 

[Retro-Protect]

Send it to Bas (theCorfiot) he's the beeb master. Unless your wanting to fix it yourself of course?

 

[dougal]

Send it to Bas (theCorfiot) he's the beeb master. Unless your wanting to fix it yourself of course?

I am discussing this on the Stardot forums and also been doing a lot of research of my own and using my multimeter. We are suspecting the issue is the NE555 (timer) which is keeping the reset line low (0v) on pin 40 of the 6502.

I am going to buy a new NE555 on Monday (its only 33 cents from a local shop) and will have a go at replacing that first.