CRO repair help.

[linux-dude]

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.

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).

Any suggestions would be greatly appreciated.

Thanks in advance,
Mike

--- Updated Friday at 11:08 PM ---

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

 

[betwixt]

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.

 

[linux-dude]

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:

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

X-plates:

Y-plates:

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

 

[KlausST]

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

 

[linux-dude]

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!