Date   : Fri, 05 Nov 1999 20:36:32 +0100
From   : "Mark Usher" <marku@...>
Subject: Re: Master Circuit diagram 

>> Well finally got my computers up and runnning. :-) It's a good feeling.
> Great!

> Care to share the details of what the problem was and how you fixed it?
No problem.
There were two problems. The first that the computer would not boot. The
second was a line jammed on the network when it did boot.

The first problem was caused by a dry joint on +5v on IC91. Found by probing
around and finally thinking - is there actually a voltage on this chip.

The second problem was a real sod. I am glad that I had a second, good BBC
to compare with.
I found that there was no wave being produced on Pin 12 of IC94. Hmmm. Pin 5
was also at +5v ! Not right.
Desoldered the socket and removed it. Still a connection to +5v. On checking
around the resistors on the solder side, just below them there was a solder
join that oh so slightly went over and onto the +5v. Hey presto, problem
solved.

The master, I put back the original MOS and it works again. I had a
different MOS on a 128K eprom "patched" into the socket. Either the EPROM is
a gonner - which I doubt - or my piggy backed patch sockets are not quite as
good as they should be. I think it's time to make a proper carrier board for
the patched MOS.

>> What i have noticed though is that there is a lack of the Master
>> 128 circuit diagram on the net.
> Didn't Acorn use to have a copy on their ftp site?  I'll see if I
> can dig it out.
Just of the BBC and econet diagrams AFAID (As Far As I Downloaded).

So now that I have my computers running, and most bit and peripherals fixed
(there's still a Watford ROM 13 board that I want to get working) - I might
actually be able to get back to doing some programming this weekend for
Babel.


Mark