Re: Tektronix 7b92a shuts down crt & graticule illumination on 7904 mainframe


Tom Lee
 

The 7B92A (and NOT the 7B92) was indeed a masterpiece, brought to us by the eminent Bruce Hofer. He broke with the longstanding Tek tradition of a Miller integrator for generating the sweep and thereby solved many tough problems in one fell swoop. The non-A version marks the end of the old way of doing things. I thought my non-A timebases were all out of whack, but after studying the circuits, I realized that they were working as well as they could. It’s a great tutorial example of the limits of a Miller integrator.

Tom

Sent from my iThing, so please forgive typos and brevity.

On Feb 7, 2021, at 1:59 PM, n49ex via groups.io <n49ex=aol.com@groups.io> wrote:

No sense hunting around all over. I would suggest go to the 7B92's connector in the back and directly check the power pins to ground. They are on the A connector side: +50 net pin 19, +15 net pin 18 (and it's most likely short C972), +5 lights pin 9, +5 pin 8; on the B side pin 18 is -15 (with it's most likely C976). Once you identify the shorted supply there (something in the few ohms or less region), THEN start chasing it down on that power net. Schematic and full maintenance manual is on TEkWiki http://w140.com/smb/7b92a_sm.pdf

I've always thought the 7B92A was an absolute design masterpiece when you think about how much functionality they crammed into this space (for the time), and the astonishing analog triggering performance. One of my all time favorite Tek accomplishments, right up there with the (7904) distributed delay line CRT deflection system - and the roadrunner meep-meep cartoon on the first edition manual schematic of the vertical output!

Reinhard




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