Re: Uncooperative 7834

Harvey White
 

On Sat, 02 Mar 2019 10:46:27 -0800, you wrote:

Hi Dave-

My favorite way to troubleshoot a scope that is in "tick mode" is to use a storage scope to make measurements of the power rails and/or the shutdown circuits during the ticks, with the storage scope in single sweep mode. During each tick, you can make measurements of the scope as it tries to start and run. So far, each time I have used this method it has led me to the failed component. Something fast like a 466 or 7834 is nice but I've also used a 549.

The other procedure that has paid off for me in the past is the use of an HP-3469B on the 1 Ohm scale to find the lowest resistance on the bad power rail, which should be very close to the shorted component.

Those two methods oughta get you there....
There's another way, that's to take a current limited supply and pulse
it on and off. For a supply of X amps, I'd limit it to x/10 amps.
Now, if you have an HP current probe, the one that's made for shorted
nodes, you can see where the bright lights go, and that shows you the
track where the short is.

You might be able to make a probe that does that.

With this same setup, you can also take a probe and with a high
sensitivity range on the scope, look for the lowest amplitude of
pulse. You'd like to measure across the component itself, if at all
possible.

This is a different implementation of the second mode.

Harvey



Best of luck!

Tom

" David C. Partridge
Mar 1 #154830

Well darn it - the power supply works just fine with a dummy load. If I
connect it to the scope the familiar ticking sound rears its ugly head."


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