[Coco] Coco Digest, Vol 63, Issue 29

[Andrew]

> Message: 6
> Date: Mon, 15 Sep 2008 03:52:15 EDT
> From: RJRTTY at aol.com
> Subject: Re: [Coco] OT: ummmm... OS-9 computer system pictures for
> 	your	viewing pleasu...
> To: coco at maltedmedia.com
> Message-ID: <d32.3d96994b.35ff6e2f at aol.com>
> Content-Type: text/plain; charset="US-ASCII"
> 
>  
> In a message dated 9/15/2008 2:14:26 A.M. Eastern Daylight Time,  
> keeper63 at cox.net writes:
> 
> Wow! A  Gimix system - I think the only time I saw one of those was in an  
> advertisement somewhere. Maybe at a computer museum. Treat that machine  
> like you would anything else of that vintage, especially in regards to  
> the power supply (caps can easily explode without warning!). Are you  
> planning on restoring it?
> 
> 
> 
> If he plans on running them he should update the power
> supplies preferably by replacing the caps or else by
> replacing the whole supply if he has to.   Man oh man
> I would love to poke around in one of those babies.  :)
>  
> Put a scope on the power supplies and look for any
> AC component on the DC voltage.  If you find anything
> but a steady DC voltage then replace the caps or supply.
>  
> I put together a functioning Mark 8 from a kit and playing
> with these machines would just be that kind of cool.....
>  
> excuse me, I have to go lay down now. I feel a little
> faint from all this excitement..:)
>  
> Roy

Well, actually the best thing would be to:

1) disconnect the power supply from the machine.
2) connect it up to a known load (some lightbulbs or something).
3) plug it into to a variac
4) set variac to zero
5) plug variac into the wall
6) over a period (day or two?) ramp the voltage up from zero to full 
voltage (110-115VAC).
7) monitor the above carefully (ie, don't leave running without someone 
checking on it to see if it is smoking or anything).
8) if nothing has exploded or otherwise died, then check for ripple, etc.

IIRC - that is the proper way to check such supplies on old machines (or 
anything of vintage, for that matter). It "reconditions" the caps slowly 
(if they have sat for a while), so they don't go "boom!" or catch fire 
on ya (which could happen by just plugging it in).

Most likely, though, you will want to replace those old caps anyway.

A lot of precaution, I know, but if you value the machine(s) and/or your 
other possessions (in your shop, home, etc), it really is "best 
practice" (although variacs aren't cheap if you don't already own one - 
which reminds me that I need to buy one for that Altair - ugh).

-- Andrew L. Ayers, Glendale, Arizona