[Coco] CoCo 1 no longer powers on (white, rev f. board)

[Andrew]

Ah, good 'ole percussive maintenance. In this case, it may not have been 
as stupid as you think. You were having a problem with noise, smacked 
it, and that more or less - very probably - showed you that it was power 
supply related (that's just a guess of mine).

Now - I don't know what noise your were getting or seeing (unless you 
posted about it earlier? I don't recall...) - but I suspect that 
something in the power supply was likely causing it, and given that it 
seems like you're not getting any power at all now - I'm thinking 
something akin to a "loose wire" or something that broke free with the 
impact (whether it's a visible thing or not, is a different question.

Maybe it was a cold solder joint (or just one letting go with age?) - or 
maybe a broken wire (hidden under insulation, or inside the transformer, 
or...?) - something of that nature.

The first place to start, though, imho - would be testing to see what 
the voltage output from the transformer is, using a multimeter. Be very 
careful doing this, of course, as there will be line voltage present (I 
don't know your skill level - so forgive me if you're like, a retired 
electrical engineer or something).

Then basically work from there (plug it back into the CoCo, follow the 
service manual on testing the PSU - ie, there should be a test point 
somewhere to see if you have the proper voltages, mainly 5 volts, for 
the CoCo to work).

That fact that you're not even getting a click from the relay, though, 
seems to indicate to me an open somewhere early in the PSU stage, so 
have a good look at the schematic, and check voltages from just before 
that point where it supplies power to the rest of the system (there will 
likely be a final-stage capacitor just before then, right after the 
(likely 7805-ish) voltage regulator, one leg hooked up to the output, 
the other to ground (and it will probably be an electrolytic).

Again - this is all guesswork on my part; I don't have the service 
manual or a schematic in front of me.

Good luck, and let us know what you find!

Andrew L. Ayers
Glendale, Arizona
phoenixgarage.org
github.com/andrew-ayers

On 2/28/22 11:19 PM, coco-request at maltedmedia.com wrote:
> Message: 7
> Date: Mon, 28 Feb 2022 13:22:09 -0700
> From: Travis Poppe<travispoppe at gmail.com>
> To:coco at maltedmedia.com
> Subject: [Coco] CoCo 1 no longer powers on (white, rev f. board)
> Message-ID:<20220228202209.GA16917 at lickwid.net>
> Content-Type: text/plain; charset=us-ascii
> 
> All,
> 
> I've got a white Color Computer 1 with a CoCoVGA board installed in it,
> and stupidly thought firmly smacking it on the side (powered off) might reseat
> something and resolve junk on the screen when powering on that recently
> showed up.
> 
> Now it won't turn on, at all, including the 'click' you usually hear
> after the fact.
> 
> Is there anything obvious I should look at? There is a fuse on the
> transformer, but it seems to be intact. Wondering what might fail easily
> with a bit of impact.
> 
> Thanks,
> -- Travis Poppe IRC: tlp on irc.freenode.net