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Tek 2235 display problem

Creede

Apr 22, 2021
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Apr 22, 2021
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Thanks Bertus

I had a data sheet. I need to figure out how it is supposed to work.
I will spend some time on it this afternoon..
Creede
 

Creede

Apr 22, 2021
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Apr 22, 2021
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After you asking if I had the scope setup properly to make the measurements, I was not sure, so I am going back and doing a do over on the measurements. It seems to take me a long time just to find the place to measure.
I also got side tracked with the focus.I got on line and tried to find out how the focus circuit works. Not much information on the subject.
Is it just a DC bias or is it far more complex?
Thanks again for sticking with me.

Creede
 

Creede

Apr 22, 2021
28
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Apr 22, 2021
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Hi
I found my X100 scope probe and looked at the focus voltage, It varies with the pot, 1600 to 1950 Volts.I have no idea if this is within the range it should be. I have read the threads you sent me. There is not much info on the web about Tek focus circuits. I have not been able to find any specs on the CRT.
Also, there is about 3 volts ripple on the focus line, Seems like that's not too bad.
I will keep at it.
Creede
 

bertus

Moderator
Nov 8, 2019
3,304
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3,304
Hello,

Perhaps a weird question, but what happens when you press the beamfinder button, next to the display?
That should show a small picture where the beam is.

Bertus
 

Creede

Apr 22, 2021
28
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Apr 22, 2021
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Hi Bertus

The beam finder displays a 4 to 5 units high and 1 unit wide
The good new is, I think I have located the problem. The focus voltage is too high. When I put the high voltage scope probe on the focus pin of the CRT, there is a voltage drop and I can almost focus the trace. There is a problem with the 6.2 meg resistor and one of the 510K resistors is out of tolerance. I have ordered parts. Finding and using the HV scope probe really helped.
I spent hours trying to find some specs on the CRT, including talking to Tektronix,. If I had known what the range of voltage to focus the scope tube, i would have been able to solve it right away. (Tektronix was no help). I think the tube is probably made for them and that is why no data is available.

Thanks for coming along for the ride.
I will post again if it really fixes it.

Many Thanks, Creede
 

Creede

Apr 22, 2021
28
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Apr 22, 2021
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It is all back together and WORKING. It was a simple repair, I just got side tracked.
A friend brought me a TeK 7514 to see if I could fix it. I have never used one of these, I will have to get a user manual just to figure out what is broke.
Thanks for your support.
This is the end of this thread
Creede
 

Creede

Apr 22, 2021
28
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Apr 22, 2021
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While in the board, R890 and R860 measured high. After carefully removing both R860 was high by about 15% and R890 was open. I tried cooling and heating it but it was just open.
As for the 7514, it is loaded with switches and at first glance, they are in bad shape.I ordered some contact cleaner and we will see what that does.I retired in 1988 and at that time we had no 7000 series scope's. I will play with it. As for the user manual, I have found it but thanks for looking.
Thanks again, it has been great having you on board.
Creede
 

Creede

Apr 22, 2021
28
Joined
Apr 22, 2021
Messages
28
A final final note.
I had to buy 100 510K resistors. If any one needs some let me know.
Creede
 
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