[sebhc] Re: H8 data record format

Dwight K. Elvey dwight.elvey at amd.com
Fri May 7 11:36:25 CDT 2004

>From: "Dave Dunfield" <dave04a at dunfield.com>
>>> Anyone have experience reviving old gear?  Mine's been boxed 
>>> for over a decade.  Any precautions I should take before I try to power 
>>> up another  unit?
>#1 - Wear eye protection. This is VERY IMPORTANT.
>     I've had a power supply cap short, causing a regulator to explode which
>     buried part of the casing in the wall!!!
>- Visual inspection, especially look for leaking, deformed or discolored 
>- Test power supply alone first. Remove all logic boards or disconnect the 
>  supply DC leads. Switchers may require a small load to operate correctly.
>- Current limit the supply. For small linear supplies, running through a 100w 
>  bulb initially is a good idea. This works ok for small switchers too, but be 
>  that the supply operates correctly on reduced voltage.
>- Use a variac to bring the supply voltage up SLOWLY - for very old long-out of 
>  equipment, take a good long time, allowing the capacitors to reform.
>  Don't do this for switchers or if the power supply is not completely 
disconnected from
>  the rest of the system.

 When I bring up a switcher that has been off for a real long time,
I often will disconnect the prinary side filter cap and put it
on a DC supply with a limiting resistor for some time. One can
also connect at most rectifiers of the switchers to form these capacitors
without disconnecting from circuits but it is best to remove
as much loads as one can. There will always be current paths
around the filter capacitor so one can't just use a limiting
resistor. Still, bringing the voltage up slowly over a day or
so is a good idea.
 The issue with most switchers is that unless they are designed
with an under voltage protection, they will often do things like
leaving the flyback transistor on constantly ( quick smoke )
or cause the switching transistor to dissipate too much power if
under load, to maintain voltage out.

>  Monitor the output as you do this and confirm that it is coming up as 
>  Monitor voltage and waveform across filter caps to insure that they are not 
shorted or
>  open.
>- Check power supply voltages.
>- Power the logic boards one at a time - If the system is small enough, 
continue to use
>  the 100w light bulb in the AC power loop - use fuses on the DC side (you will 
have to
>  estimate power requirements for the boards).
>dave04a (at)    Dave Dunfield
>dunfield (dot)  Firmware development services & tools: www.dunfield.com
>com             Vintage computing equipment collector.
>                http://www.parse.com/~ddunfield/museum/index.html
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