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CRO repair help.

linux-dude

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Hi all.

I'm repairing an old Kenwood CS-5130. The first problem was that the blanking circuit was broken, I found and replaced a dead diod. I also replaced associated caps that i suspected was the root cause, see image.

repair.png


After i fixed the blanking circuit, i found another problem that confuses me. After about half the sweep X and Y axis are heavily distorted, se video.




I have checked X and Y deflector voltages and do not see anything strange. Below an image of X-deflection voltage (blue) and the blanking voltage (yellow).

Screen Shot 2023-05-27 at 5.42.25 AM.png


Any suggestions would be greatly appreciated.

Thanks in advance,
Mike
--- Updated ---

I removed the time base circuit from the equation by using X/Y mode. The distortion remains the same.


 
Last edited:
I suspect some of the horizontal timebase signal is getting back to the vertical deflection circuits. As a guess I would suspect the power supply rail has a dried up capacitor across it. Use the other scope to check the supply to the Y amplifiers.

Brian.
 
Thanks Brian.

The power rails (12V, -12V, 140V) is within 1% and less than 30mV p-p noise.

If i set the scope in X/Y mode and apply a 1Khz sinus to both channels i get this:

XY.png


With this setup, the following is measured at the back of the tube:

X-plates:

X plates.png


Y-plates:

Y plates.png


To my eyes the distortion on the trace is not present on the deflection plates, or am I missing something?
 
Hi,

off topic:
2.1MBytes is rather big file size for the "infromation" in the picutre.
As a linux guy you could just convert it to .JPG with 30% quality setup and get less than 10% of the file size.
(PNG is not good for photos)

Or use an online "picture converter tool".

Klaus
 
Hi,

off topic:
2.1MBytes is rather big file size for the "infromation" in the picutre.
As a linux guy you could just convert it to .JPG with 30% quality setup and get less than 10% of the file size.
(PNG is not good for photos)

Or use an online "picture converter tool".

Klaus
Apologies, will keep this in mind for the future!
 
Could this be mechanical in nature, i.e. that the internal geometry is tilted or broken? It would make sense as the issue seem bound to physical locations on the CRT display.
 

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