Adam Goldman wrote:
I just bought a used Tektronix TM504 power module and would like to test
it before I put any plug-ins in. I plan to first ESR test any caps, then
check the pass transistors with a DMM diode test function, and finally
power it up and make sure all the voltages are in spec. Oh, and then
remove any inter-module jumpers and connector barriers. Is there anything
else I need to do?

I don't have a curve tracer to fully characterize the pass transistors. I
guess if it's necessary I could throw something together with a doorbell
transformer or whatever. I wouldn't be very good at interpreting the
graphs, though.

My DMM also has an hFE mode if that's any use.

Thanks for any assistance!

-- Adam

Virtually every TM500 mainframe I've bought used had at least one bad
pass transistor.
Checking them with an ohm meter is definitely better than nothing.
But...they're often overheated for long periods of time.
On a curve tracer at high current, they can look more like resistors
than transistors.
Breakdown voltage can also come way down. Beta can go to hell, then the
driver in the plugin overheats and shorts out blowing up the plugin when
the voltage goes to the rail.

Also reheat all the transistor solder junctions. The heat tends to
crystalize the solder over a long time. Make sure the mounting nuts are
still tight.

I wouldn't sweat the ESR of the caps. Just put on a load and look at the
ripple. IIRC, full load minimum line should have a trough voltage of at
least 22V on the 25V supplies. Don't remember the number for the 11.5V,
but think it was 7V trough. But it's been three decades since I worried
about the numbers.
I've never seen a bad transformer, but expect they exist.

Take a good look at the connectors. Replace the plastic key. You
wouldn't think it important, but it helps guide the plugin so you don't
blow it up when you plug it in hot...at least not as often. Same thing
can happen if the top and bottom of the connector wears on the
fiberglass and lets the plugin slop up and down.

And use your expendable plugin to test the hole for the first time.
mike

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