Cambridge Workstation woes - VMS 2691 PSU smoke

Tony Duell ard.p850ug1 at
Sun Jul 30 14:28:14 CDT 2017

On Sun, Jul 30, 2017 at 8:17 PM, Jules Richardson via cctalk
<cctalk at> wrote:

>> The former are the ones that normally fail, but I would change the lot.
> I'd be inclined to agree in the case of any class X/Y caps as they're a
> known failure point in any piece of vintage equipment... but not every
> single cap in the PSU. I know that's not what you're suggesting, but there
> seems to be a trend amongst collectors to blindly replace every cap in sight
> as part of some "refurbishment process" these days, whether they're good or
> bad. Personally I like to keep my systems as original as possible, which
> generally precludes replacing perfectly-good vintage components with
> perfectly-good modern ones :-)

Yes, I was not clear. I don't believe in replacing perfectly good capacitors
either, and in my experience capacitors (at least not in classic computers)
do not fail as often as some people will have you believe.

I meant to say to replace all the capacitors in the mains filter circuit. There
will probably be a bfilar-wound filter coil (which doesn't need replacing). On
one side of it (electrically) will be a class X capacitor between live and
neutral and a pair of class Ys from each of those line to earth. On the other
side of the filter coil expect at least the class X between live and neutral
maybe more class Ys to ground.

I would replace all those. And nothing else unless you know there's
a fault.

Thinking about it, the ACW has a built-in Microvitec monitor with its
own SMPSU (on the monitor board). That probably has its own mains
filter componets which I'd probably replace while I was in there.


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