Date   : Fri, 27 Jul 2001 04:22:49 "GMT"
From   : "mikef@..." <mikef@...>
Subject: Help with BBC B fault

Hi,

I've been given a BBC B which I'm trying to get working again. It's suffering
from the dreaded single 
continous beep fault. I know this symptom is quite common when the B fails
and I have tried all the 
normal fixes I can find. It is a standard Issue 7 board with 8271 upgrade.
So far I have tried:

replacing the keyboard
replacing the power supply
replacing all the socketed chips (6502, 6522, Video ULA, OS ROM etc.)
changing the memory bank jumper (25) to all 3 combinations

I don't have an oscilliscope or a logic probe, just a multi-meter, so it's
difficult for me to test the 
circuit board directly. I did notice that the current from the jumpered pins
of PL25 to the unjumpered 
pin was oscillating quite noticably, if that means anything.

Can anyone suggest other things to try that may solve or narrow down the
problem? Could it be a faulty 
SA5050? Also, what happens between the machine issuing the first and second
beeps?

Thank you,

Mike.

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