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CTM-644 Vertical Rolling Issue

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kbjunkie:
Hey all,


I'm having a look at my CTM-644 colour monitor and the screen is rolling continuously - and when adjusting the V-HOLD on the back, I'm able to slow down the roll, but not get it to lock.  I've cleaned the VR405 (20k pot) with some contact cleaner and checked it out of circuit with a meter and it seems smooth enough - seems to go from about 50R to 18.5K.


If I very gently turn the pot, I can sometimes get the picture to stop rolling, but on a switch off/on it just starts rolling again.


Does anyone have any ideas?


Thanks,

Mark.

Animalgril987:
Dirty contacts on the DIN connector maybe?

Bryce:
The DIN connector has no influence on the V-Hold.

VR405 should go from 0R to 20K, so there's probably still lots of dirt in there.

Bryce.

kbjunkie:
Hey Bryce,

Cleaned the DIN - it was fine.


I've cleaned the pot within an inch of its life :-)


There does feel like a small spot on it that kinda grinds, right at the very end of clockwise travel.. I may have to try replacing it - any idea where spares can be found?


Cheers,


Mark.

Bryce:

--- Quote from: kbjunkie on 17:01, 27 May 21 ---Hey Bryce,

Cleaned the DIN - it was fine.


I've cleaned the pot within an inch of its life :-)


There does feel like a small spot on it that kinda grinds, right at the very end of clockwise travel.. I may have to try replacing it - any idea where spares can be found?


Cheers,


Mark.

--- End quote ---

As stated above, the DIN connector has no effect or influence over the V-Hold, so cleaning it would definitely not solve the issue. You could try replacing R412 with a slightly lower value. I have no idea what the dimensions of the original VR is, so I can't suggest replacements.

Bryce.

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