Date : Tue, 14 Apr 2009 00:25:57 +0100
From : dm.hunt@... (David Hunt)
Subject: Easter Disaster
> I was measuring somewhere on the motherboard. I know I did the Teletext
> chip at one point because a screenful of random Teletext characters
> appeared.
> Apart from that I don't remember anything unusual happening. I've
> measured
> the power connector voltages since the disaster and they are giving the
> correct
> readings. I've also measured most of the chips and they all seemed to be
> giving
> 5V or thereabouts, with the exception of the 26LS30 which was giving me
> about
> 9V.
>
> There aren't any socketed chips so all I have been able to remove are the
> MOS
> ROM and the keyboard, which I have tested in another machine and they are
> working.
>
> I left it on for a few minutes with the speaker unplugged and some of the
> chips
> were getting warm like the vidproc and Teletext chip, but some others,
> which
> I can't just recall offhand, were stone cold. Which is good - warm or
> cold?
>
> Best wishes,
>
> Ian
If the ICs are all soldered on the board then you're in for some
de-soldering. Tracking down the fault is the first hurdle though, you're
going to need a dual beam scope, at least 20MHz. Work your way around the
board checking the voltages and frequencies at various points (see Service
Manual) to try and find the dead IC(s). I don't envy you the task, it might
be easier to change motherboard or machine and use that one for spares.
Dave