Electronics > Repair

Tektronix TDS540 Screen get twisted and garbled after 30minutes of use

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lugaw:
The screen seems to be getting bigger and bigger after 30minutes of use and after that it get twisted.  After cooling if off it goes back to normal.  It doesn't seem to affect the other function of the scope.

I haven't open it up yet to test voltage. What could be the issue? Is it a simple power supply or the flyback transformer is dying?

image_tek2.jpg is the normal screen on startup and image_tek1.jpg is when it has expanded a bit after 20mins.

CaptDon:
Um, it would have been nice if what you were trying to display was the same in both pictures. Without the on-screen menu and so forth in the second picture it is a bit hard to compare apples to oranges???  Try it again, leave all the settings alone and show us before and after.

factory:
The text for "Tek running" in the top left has partially disappeared off the screen, looks as if the whole imagine has increased in size.

David

TheBay:
It does seem to be a EHT issue, it would be useful if you could measure it at the PDA.
Then it could either be a LOPT fault or the H drive circuitry.
Does the LOPT feel hot after it has been on for a while?

shakalnokturn:
The H drive and LOPT are in the same circuit on the TDS540.
Anyway +1 for the LOPT being defective, I had the same scope with exact same symptoms.
You may also find that the current draw rises and regulated 21.5V (? Off the top.of my head) droops a little as it warms. You'll notice the regulator's heatsink is very hot.
ISTR posting on groups.io about mine.

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