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Old 29th May 2016, 2:25 am   #1
Mitch-W
Tetrode
 
Join Date: Feb 2015
Location: Celje, Slovenia
Posts: 70
Default Tektronix 2213 Auto intensity problem

Hi, I had this scope for my main use for almost 8 years now, when I stared with electronics. I got it for almost free, and it was working okay for my use. I only needed to replace paper RFI Rifa Y capacitors on the SMPS part, because one had burned, but this was long ago. There was always a bit of an issue with a auto intensity control, as the screen wasn't that bright on higher sweep speeds. But today, when I have it on the highest sweep speed ranges, the trace goes almost 100% dim (barely visible in the dark), of course with the Auto intensity pot turned all the way up.

On the slower speeds, it seems to hold the trace brightness well, also I can adjust the brightness all the way from the completely dark, to the point of blooming. The trace brightness will be stable until I hit about 0.1 ms mark, then I can clearly see that the trace gets dimmer with each step further.

Also if I hit the Beam find control, the trace is displayed with the two "dots" on each side. But also, if I go beyond 0.1 ms, the "dot" on the right side gets dimmer than the one on the left (left one seems to hold the brightness through the whole sweep range).

I have the service manual for this scope, and it suggests there is something wrong with an Z axis control or the Auto intensity control. I checked the voltages, and it seems that on the U835B pin 8, I don't get the right voltages, if I turn the Auto Intensity pot, but the circuit is too complicated to follow. Also If I had another scope, I would be able to check if there is Swp duty signal, and so on, to find out which one is missing, but sadly, this is my only scope.

Service manual: https://www.hellspark.com/dm/ebench/...13_service.pdf
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Old 31st May 2016, 3:50 am   #2
tony brady
Hexode
 
Join Date: Mar 2014
Location: Peacehaven, East Sussex, UK.
Posts: 278
Default Re: Tektronix 2213 Auto intensity problem

pin 8 of U835B is the positive power rail shown as +8.6V. what voltages are you getting on pin 8 & pin 4?

or did you mean to say pin 7?
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