Electronics > Repair

Unable to perform CAL08 in a Tek 2465B- now vertical position not working (4 ch)

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rodd:
Hi folks,
I was performing the CAL08 procedure as suggested in other trend to fix a four rows of dots that are showing on the screen.
First, I could not adjust grid bias trimpot (R1878) because the spot was MUCH MORE brighter than the line of dots for the entire pot range.
The the display flickered and the dot became a lot less brighter but still brigter that the dots, but I decide to move on.
When I started the geometry adjustment moving R4350, the scope rebooted and the vertical position controls for all the channels are not working
The scope is able to display the calibration signal, but it is high "up" for CH1 and CH2.
Just in case I checked the voltages at J119 and they are all fine.
I went to the troubleshooting chart but it is very "vague" to me.
It says " if the problem happens on the four channels the problem can be:
1-  channel switch
2- delay line
3- Vert Output Amplifier
4- Hybrid Power Suplies

I do not have enough knowledge to proceed.
Any suggestions?
Thanks to all,
Roger

rodd:
Another observation:
The scope is capable of displaying a signal that is aplied to any of the channels.
The gain and sweep time seems to be working.
However, I can not change the position of teh waveform that is displayed.
Is this an indication that the problem is in the A5 board?
Roger

MathWizard:
When you say you moved R4350, is that a trim pot on the inside of the machine? or a knob on the outside ?

If it's inside, did u maybe short something with a screw driver ? Or maybe it's an old trim pot, that's dirty/corroded, or cracked ?

IDK the circuits or this scope, but can u check the voltage(s) out of R4350 to see if it changes ?


What do u mean the scope rebooted? Did it have a short or something and trip some protection ? Maybe something in your adjustment circuit failed when u changed it.

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