> >Good point, there's also the issue of flux which I believe can
> >also cause problems in rare cases (I recall once reading about
> >a fault that Alex Yeckley (I think) came across which was
> >caused by flux from a previous repair causing some slight
> >conductivity).
>
>Wow - I'm amazed that anyone remembered that.
I'm amazed too! :)
>It was in an op-amp circuit
>where the currents were very, very small (input impedances of megohms-plus)
>and any leakage current caused weird things. I don't think that's what he's
>got in this case. If I were a gambling man, I'd bet that he's got a solder
>whisker - perhaps microscopic - somewhere between one of the data lines and
>some other signal.
Well, only just made a very interesting discovery ........ the vector PROM
(Atari code 36408 at location K7) is socketed, and removing the PROM
'fixes' the problem as far as the Fluke RAM and ROM tests go, AND enables
the running of the board 'blind' (the vector state machine is disabled as
I've clipped pin 6 (HALT) of the LS244 at location R11).
Have tried a known good PROM and the problem returns.
I'm now going to replace the socket and see if that helps .............
Phil
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Received on Tue Aug 29 18:44:26 2006
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