Powering up a 20-year old MicroVAX II

Rod Smallwood RodSmallwood at mail.ediconsulting.co.uk
Mon Feb 23 01:27:13 CST 2009

   Sounds like capacitors. 
Alhough it's a switcher any high voltage/high value capacitors in the
PSU might well need reforming.
Quite often you will see caps with a pair if incised lines on top. This
makes them go pop instead of bang.
You would not want to see a PSU where they have gone bang.

Rod Smallwood

The DEC Collector

-----Original Message-----
From: cctech-bounces at classiccmp.org
[mailto:cctech-bounces at classiccmp.org] On Behalf Of Robert Jarratt
Sent: 21 February 2009 19:17
To: 'General Discussion: On-Topic and Off-Topic Posts'
Subject: RE: Powering up a 20-year old MicroVAX II

> -----Original Message-----
> From: cctalk-bounces at classiccmp.org [mailto:cctalk- 
> bounces at classiccmp.org] On Behalf Of Robert Jarratt
> Sent: 20 February 2009 22:45
> To: cctalk at classiccmp.org
> Subject: Powering up a 20-year old MicroVAX II
> I have just collected a MicroVAX II which has been in storage and has 
> not been powered on for 20 years. This is my first machine of such an 
> age, unfortunately I am not particularly knowledgeable at the 
> electronics level (I studied circuits academically 25+ years ago and 
> can solder a bit, but that is as far as it goes). I know I will need 
> to treat it carefully in order to get it working again. I plan to open

> it up and make sure I clear out any debris etc, but beyond that I need

> advice from those with the experience and knowledge that I lack on how

> to go about powering it up carefully.
> Thanks
> Rob

After removing all the boards and leaving just the disk and tape drive
for load I impetuously decided to try powering it up. I knew the PSU
H7864) was set for 110V and made the switch to 240V (I am in the UK).
When I connected the power cord, after a few moments there was a loud
pop, followed by another before I could pull out the power cord, smoke
rose from the PSU.
This sounded just like when I had once accidentally made a 110/240

The question is, could it be that I had not made the switch to 240
correctly, or could this just be down to the age of the PSU?



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