Re: How to troubleshoot a faulty 7B92A?

Harvey White

Replies interleaved:

On 3/18/2021 7:03 PM, Thierry Delaitre via wrote:

I have a faulty 7B92A that I would like to repair

I have a 7704A as a scope
OK, a little fast for the 7704A but that only shows up on the fastest sweeps.
The jumper for mainframe selector is on P835 for "other 7000"
I think that's right, the other setting may be for a 7854, which makes a difference.  I think it may end up changing where the illumination power comes from.

I am not sure if the jumper for time/div variable selector should be on P760 (delayed) or P761 (delaying) for the 7704A ?
Either is valid.  It depends on how you decided to use it.  You'll get different behaviors, of course.

There is nothing showing on the screen when pressing the beam finder button
And I'll assume that the beam finder works properly with another horizontal plugin.  So it's not the switch.

When the 7B92A module is inserted into the scope, the trace displayed by the other timebase is vibrating a bit and it can be observed that the position of the readout is different for the other timebase/input.
What I'd suspect is that the output of the plugin is out of scope (!), that is, is going between  extremes at the horizontal input stage.  In other words, the plugin is driving the horizontal input of the mainframe badly.

Do you have any recommendations on the approach for troubleshooting a 7B92A?
Check the power supplies first, in case there's too much loading from a bad capacitor.

Look at the output to the scope, it ought to be wrong.

Crosstalk from H to V and between the H channels can happen with the trace deflected off the screen.  A symptom is that you may see the displays (and other trace) wiggle when the 7B92A sweep triggers.  The rate of "wiggle" may vary with the sweep settings.

I'd suspect all of the outputs from the plugin until I have verified that they work.




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