BBC model B computer help please

[Traindriver69]

Hi all
I have just picked up a BBC computer and tried turning it on and just get a continuous buzz with two lights lit and no picture.
So I have tried looking online but can't find any details on the version I have inside on the motherboard it says 0233,000 ISS 1 copyright 1984 and on the bottom there is no normal BBC serial number but it says instead
Cleartone Abercarn Gwent 105099.
Many thanks in advance

 

[Malc]

It's an early issue 1 by the sound of it, The first thing i would check is the PSU, Cap failure is a common problem on OLD beebs, http://www.sprow.co.uk/bbc/howto.htm#powersupply Be extremely careful when working on PSU's, If you have no experience seek help from somebody who does.

 

[g4ugm]

Continous buzz is usually a failure to exit reset. Lots of info around the net. e.g.

http://8bs.com/mag/37/bfaults.txt


One of the PSU fix kit vendors on E-Bay includes a CD of articles from the net on fixing BBC.

 

[daver2]

+1 - buzz = CPU still (effectively) in reset - or otherwise failing to run when it should.

Check the power supplies first (as Malc has already stated) and then check the CPU reset and clock lines for activity. Get the CPU datasheet for the pinouts of the CPU and for the reset and clock pins and levels.

Because the BBC is 6502-based - you will find a lot of this information over on the Commodore (PET) thread already. Just search for posts by myself or dave_m.

Dave

 

[drdanj]

Traindriver's getting some help over on stardot by the looks of things, but just incase anyone else comes across this thread. The PSU issues are usually around the X2 capacitors exploding - the PSU will continue to work after this happens, it'll just stink. Generally the PSU is pretty reliable. Continuous tone means that the OS isn't booting and the SN76489 isn't being initialised. First port of call on that one is usually the system 6522 - if it's not behaving it'll stall the boot process. Failing that it's invariably something in the RAM circuitry (either logic or RAM itself). There are other things that can be up the spout, but those are the most common.