Re: faulty power supply?

[Allen Bong <allenbsf6502@gmail.com>]

On Jul 9, 6:34 am, jonnosan <jonno...@gmail.com> wrote:
> My enhanced iie will no longer boot if I have either/both of the SSC
> or disk controller card in it. It powers up, but only displays think
> vertical bars.
>
> If I remove both the SSC and disk controller, it boots up fine.
>
> I tried this on another mother board and got the exact same behavior.
>
> If I remove the keyboard, I get the same bars when a card is in a
> slot, and the self-test if no cards are plugged in.
>
> the 64K RAM card doesn't appear to make any difference (i.e. system is
> the same whether it's plugged in or not).
>
> Can a faulty power supply cause these symptoms?
>
> Regards
>
> Jonno

May be the SSC or the disk drive card is faulty causing the problem.
Did you get a good SSC and drive cards to replace the faulty ones and
see what happen?  These cards are quite common, you should be able to
get one easily on eBay.  Most probably data lines on the cards are
having problem.

Why did you suspect the power supply?  Are your A2 overloaded with
power hungry cards?  Well, if you have a cheap digital volt meter, you
can measure the voltage across pin 7 and pin 14 of any 14 pin ttl chip
and see if the voltage is around 5V  +/-5%.  Measure with and without
the suspected cards in and see if there is a big difference (say below
4.5 volts).

Without further clues, that's I can think of this moment.  I wish you
luck in restoring your A2 back to normal again.

Allen