6 Feb
2006
6 Feb
'06
5:26 a.m.
Pete asked:
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 for
smoke.
Does this seem an appropriate plan? Can anyone point me to pinouts for the
various supply leads from an H7864?
Does anyone have any other recommendations/experience of going though this
process, and is there anything I've missed that I should have included
above?
Just plug it in and turn it on.
Unless the economics have drastically changed in the past 5 or 10 years,
a uVax II in a BA23 has a street value of $50 tops. If there's any irreplacable
components/assemblies/drives you may indeed want to remove them during
initial testing (in any event as you reconfigure the system you certainly want to
start with the simplest "has to work" configuration and then add on all the
unknowns.)
Ignore anyone who tells you to bring this up on a Variac. You will be increasing
the chances of damage by doing so. Variac's are great for linear supplies in
reforming electrolytic caps, but they only make life worse in a switching
power supply because you're gonna cause all sorts of out-of-usual
conditions. See, a switching power supply has negative impedance as seen
from the "in" connector: if you decrease
input voltage,
it will increase its current draw to keep power out constant. Outside
of a
reasonable range (say +/- 30%) of input voltage the flyback pulse widths etc. will
be seriously out of whack too, also probably triggering a shutdown.
My personal preference with linear supplies is to just plug it in and let any
bad electrolytics blow up :-).
The BA23's power supply (like most switching supplies) has more than adequate
shutdown-on-overvoltage-out circuitry.
The one thing to check: look at the 0.156" spacing harness from the PS
to the backplane. Wiggle it on and off, look for charring and overheating. Some
signs of past heat are likely, but if any of the contacts are burnt up you
might want to look for or fabricate a different jumper. Worst case will be that
you burn up the jumper, and you won't be the first to have it happen!
After you get it up and going, you will probably find that the NiCads that
hold the CPU configuration and run the TOY clock don't hold a
charge. It's just 3 AAA's in series. It's not really necessary if you
don't
mind setting the clock and selecting the boot device manually
at every startup. NiMH's are more available today and
probably a better technical choice for replacement if you decide you need to
TOY clock and config RAM.
Tim.