[Coco] CoCo 2 with Random Characters on Screen at Power Up

[Arthur Flexser]

The fact that it works for 10 seconds suggests the possibility that
something is overheating.  Especially since it only takes 1 second if you
try again immediately afterwards.  Possibly that 6821 PIA chip that isn't
socketed may be the culprit.
(I base that on having once encountered an equivalent chip in a
Commodore-64 that had an overheating problem that crashed the machine after
a few seconds of normal operation.)   Are any of the chips particularly hot
to the touch?

If one of the chips seems suspiciously warm, try putting a couple of ice
cubes in a plastic bag and hold them against the suspect chip.  Does this
lengthen the interval before the crash occurs?  If so, I'd say you've found
the guilty chip.

Art


On Mon, Jan 27, 2014 at 2:18 AM, Danny Amborn <slackware64 at embarqmail.com>wrote:

> On Sun, 26 Jan 2014 21:45:38 -0500, Arthur Flexser <flexser at fiu.edu>
> wrote:
>
> >I would now try putting the 6847 back into your previously working CoCo
> and
> >seeing if it still functions okay.  It sounds possible that the bad CoCo
> >may be damaging 6847s that were previously okay.  This is particularly
> >possible if you tried the previously working 6847 in the bad computer
> >while that computer still had the bad 6809 in it.  Or you had the bad 6809
> >swapped into the good computer and the presence of the bad 6809 maybe
> >damaged its 6847 when you turned that computer on.  You may now need to
> >order one 6809 and two 6847s to put things right, if I'm surmising
> >correctly that the bad 6809 may be a 6847-killer.
> >
> >Art
>
>
> I was actually worried about that too so I did put the 6847 back into
> the original computer and it works like a charm.  I also took the CPU
> that I originally dropped into the non-working computer, a 6309, into
> the working computer and it also works just fine.  At least in the
> short time I had those chips in there it hasn't damaged them.
>
> --
>
> Dan Amborn
> slackware64 at embarqmail.com
>
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