powering up older machines - is it safe?
lbickley at bickleywest.com
Tue Jun 3 17:24:13 CDT 2008
On Monday 02 June 2008 18:13, Tony Duell wrote:
> > Anyway, a friend asked me to try and sell a DEC Robin for him (he tells
> > me it's a DEC VT180 with a separate drive unit that he tells me was only
> > available to DEC employees), and my question is this:
> > Is it safe to try and plug this machine in and try to power it up?
> The main worry is not a capacitor Failing. The main worry IMHO is that if
> there's a fault in the power supply regulation circuitry then that could
> make the +5V line jump to a high enough voltage to wipe out just about
> every chip in the machine. Expansive and difficult to put right.
I'm in strong agreement with Tony on this. With most vintage equipment I
restore, I do the following:
1. Test all power supply capacitors with an ESR meter and/or a VOM.
2. Where possible, remove all modules from a system before applying power.
3. Check to insure that there are no shorts between any power leads (I've
found springs, screws, etc. under motherboards and backplanes - which would
have created major power shorts.)
4. When the above check out correctly, apply power and test all voltages for
the proper level. Test for (appropriate) low AC ripple in all supplies.
5. Power off. Insert the minimum number of modules to test the system
(assuming it's a mini or micro) - such as CPU, Memory and Console I/O. Power
on and test.
6. Once #5 is successfully completed, insert modules by function and test
until all modules/functions have been tested. (Obviously powering off before
module insertion and off after testing).
Some pieces of equipment don't lend themselves to all of the above, but lots
of gear does.
Patience is the keyword. Never be too anxious to apply power. (Unless, of
course, you don't care if something gets zapped in the process ;-)
In answer to the question - have I ever seen a power supply go "crazy"? YES!
I've seen a linear 5V supply put out near 15V - which, if modules were
present, could have had nasty consequences. I've see more that one switching
power supply "create" very "off" voltages as well.
Speaking of patience - those of us working on the PDP-1 restoration at the
Computer History Museum didn't power up the system for several months while
we tested and reformed all power supply capacitors, tested all power supplies
for proper voltage, ripple, load characteristics, etc. :-)
Bickley Consulting West Inc.
Mountain View, CA
"Black holes are where God is dividing by zero"
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