Cambridge Workstation woes - VMS 2691 PSU smoke

Jules Richardson jules.richardson99 at
Sun Jul 30 11:18:18 CDT 2017

On 07/30/2017 10:59 AM, Ian Frost via cctalk wrote:
> Any body any experience in fixing these old Acorn PSUs - or managed to
> source alternative modern supplies?

There wasn't anything "special" about them, in that the outputs were 
typical for "small computer with a hard disk" (i.e. +5V and +12V at a few 
amps, -5V and possibly -12V, main regulation done on the +5V rail, "hard 
start" via physical switch).

I expect it's possible to find a modern PC PSU in some kind of slimline 
form-factor which will physically fit (and rig the soft-start so that it 
powers up as soon as AC is applied). I expect the current limits for the 
different rails are printed on the side of the VMS PSU's frame, so 
as-good-or-better should be fine.

Unfortunately I did trace out some, possibly all, of that PSU (most likely, 
it was certainly a VMS-something in my ACW) years ago, but even if I do 
still have the schematics, they're on the other side of the Atlantic. The 
PSU in mine had the rectifier diode on the +12V rail go intermittent,  so 
it would start sometimes and not others.

Tony D. might have schematics, but I have a feeling they weren't part of 
the ACW service manual as the PSU was bought in from an external supplier 
and not an Acorn part.



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