Powering up sleeping uVAX II

Tony Duell ard at p850ug1.demon.co.uk
Mon Feb 6 17:54:40 CST 2006


> 
> At 12:49 AM 2/6/2006 +0000, you wrote:
> >Hi List,
> >
> >I have here a uVAX II in a ba23 box, most likely not powered up for 2 or=
>  3
> >years.
> >The innards are clean, no nasty smells, no other trace of prior problems.
> >Even so, to minimise the risk of damage I'm going to disconnect all the =
> 5v &
> >12v leads, then attach some suitable dummy load(s), switch on and wait f=
> or
> >smoke.
> >
> >Does this seem an appropriate plan? Can anyone point me to pinouts for t=
> he
> >various supply leads from an H7864?
> >Does anyone have any other recommendations/experience of going though th=
> is
> >process, and is there anything I've missed that I should have included
> >above?
> 
> All wise precautions. Many others recommend also using a variac to bring =
> up=20

It is a very bad idea to 'run up' a swtich mode PSU (which this is) on a 
Variac. SMPSUs appear as conatant power loads, as the input voltage 
decreases, the current increases. Some supplies will blow their chopper 
transistors under such conditions. 

If you want to re-form the capacitors (and I don;t think it's necessary, 
I've never had problems with capacitors in computer power supplies), take 
them out of the circuit, and reform them using a bench supply and a resistor.

One thing I would recoemnd is that you check all the fans are running. If 
not, either replace them or repair them (I do the latter...). 

-tony




More information about the cctalk mailing list