[Coco] CoCo3 power short?

Tim Fadden t.fadden at cox.net
Thu Nov 2 16:08:17 EDT 2017

If the caps are original, I would suspect them above all else not 
counting any manually caused short/human error. :-)


On 11/2/2017 12:57 PM, dwight.bazinet wrote:
> I asked this question on the Facebook page a few days ago, but I hope you
> don't mind e repeating it here?
> I recently got a CoCo3 off EBay, a CoCo SDC from Ed (and had a case
> printed) and a RGB to SCART to HDMI from Richard.  Everything was working
> fine except a small video problem; ironically it was while I was talking to
> Richard about the video that something went wrong.
> I turned the computer off then on and it didn't come on, and started to
> buzz.
> I've isolated the buzz to the relay, it seems what is happening is that the
> SALT is detecting an over current and dropping in and out.  The input to
> the power transister is around 11.8V, the 5V output is around 2V.  The drop
> over R19 is only 25mV, well under the 150mV the service manual says it
> should be, indicating a short.
> I thought maybe the RGB hadn't been used in a long time and one of the
> transistors broke down to short, I removed all three, but that wasn't it.
> There does look like glue around the bottom of the two large power
> capacitors which has dried and cracked, so I may remove them and check them.
> So I'm facing a failed component which is shorting power to ground, with
> the only way to isolate being to remove each one in turn, with most of them
> being soldered in...
> Any suggestions on which ones to start with? I already tried the GIME.
> Thanks

Tim Fadden
"Hey Schmidt, don't forget about the six P's.
Proper Preparation Prevents Piss-Poor Performance!"

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