Tektronix 453 trace way off-screen horizontally

Sep 12, 2006 5 Replies
W

Hi all,



I recently got hold of an old Tektronix 453 oscilloscope. It seems to work just fine, but the trace seems to be way off-screen horizontally:



When I press the "beam finder" button, which is supposed to compress the display to fit all of a trace, I can see the trace running as a dot that moves about 1/16th of a div at a position of approx 75% of the display's width. I can adjust the horizontal position of that dot by about 1/2 div. When I release the "beam finder" button, I get a horizontal streak to the right and the trace is gone again.



After opening the cover and measuring the horizontal deflection plates' voltage (to ground), one plate constantly read approx. 110V, the other



0V, which seems to be off-scale - I expected something like a sawtooth of approx. 75V on both. When I shorten the plates, the dot is dead-center.

Could it be that something is wrong with the horizontal amplifier circuit?



I hope this is a common fault of this series and you can give me blind advice on where and how to check for errors - I wouldn't know where to start...


Thanks in advance,



Wolf



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N

Swap the two final driver trannies or replace them both with something voltage/current-wise suitable and see what happens, go for proper replacement later if nominally corrected.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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A

first get a manual from

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or similar place.

Then try rotating the front-panel accessible screwdriver trimpots.

They often go intermittent. Then try wiggling the under-chassis horizontal related trimpots.

Before you spend very much time on this-- if the trimpots behind the panel are intermittent, or the Nuvistors are weak, consider junking the scope. The Nuvistors are hard to find and expensive. It's a major disassembly job to get to those trimpots, pry them open, and squirt cleaner in them.

All of the power supply capacitors are likely to be on the verge of going bad. The high voltage cage is likely to have a component or two short out within the next 10 hours.

Don't ask me how I know this. :)

( They're very pretty scopes inside, with all that gold plating and expensive looking components, it's just that many of them will require LOTS of TLC and expensive or unobtainable components. )

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M

Do you have it set to a free running mode? If not, the beam is held to the side waiting for a trigger.

Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
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W

2N4125

Thanks alot! The driver transistors were also my prime suspects.

Thanks also to the other posters and sorry for not responding earlier. I'll check it out this weekend and let you guys know if it worked.

Kind regards,

Wolf

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