[Coco] 128K CoCo 3 is DOA D:

[Rogelio Perea]

On Sat, Oct 6, 2012 at 1:12 AM, Juan Castro wrote:

On turning on, there's the familiar VDG green with black border -- but
> no text. Turned it off quickly and opened it. There seems to be some
> busted capacitors by the left. Could these be the sole cause of the
> problem? (Please don't tell me I have a busted GIME.)
>

>From the pictures there is apparently some brownish goo around the big
power supply filter cap. This either could be dried up electrolyte busted
out of the cap or the glue used while manufacturing to hold the caps on the
boards as it is wave soldered. Does it smell funny? like an acrid pungent
and yet sweet (some may say that) odor? that's a clear sign of leaked
electrolyte.

Given the fact that you can see a green screen it looks like the power
supply is working. A shorted filter cap will blow a fuse and that's the end
of it, no chance to see any video.

Check the caps for possible shorts or opens, if you have a multimeter you
can see to a certain degree of positive proof that they either are good or
bad. You will have to desolder the caps and test them out of the board,
otherwise it is harder to say on their condition.

If the caps are good (I have never had any cap problems on any of my CoCos
ever since new), check the socketed GIME chip. Unplug power and remove the
ram expansion and the GIME chip, blow some compressed air into the RAM and
GIME sockets, inspect the pins of the GIME - they should be shiny clean,
any dust/lint/grime should be removed carefully. Once done reseat the GIME
in its socket fully in, make sure is even within the socket, install the
RAM back again and try powering up now... I have seen many CoCo 3s get back
alive only by reseating the GIME.

Let us know.


-- RP