Commodore 1702 Monitor - No Color After Re-capping

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lothian
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Commodore 1702 Monitor - No Color After Re-capping

Post by lothian »

My 1702 monitor worked great with my C64 for years. After it failed to display recently, I decided to re-cap the thing as the tried-and-true fix all. There must've been a bad cap among the 39 I replaced 'cause the monitor powered on with no snaps, crackles or pops, and I get a picture from a C64 source.

However, there are two issues:

1) The monitor does not display color; and
2) retrace lines are visible.

The first things I checked were the color pot on the front panel, the front/back video inputs, the switch selector, and the cables. None of these things are the source of the problem. I can think of just two ways to mess up a re-cap job: installing incorrect spec cap and reversing cap polarity.

Obviously the problem is limited to video signal processing, which should limit the number of caps to scrutinize. I looked over the suspects with a borescope: cap specs and polarity for each are correct.

I'm stumped.

Any electronics engineers in this forum with experience t'shooting this type of issue with a Commodore 1702 monitor?


rmzalbar
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Re: Commodore 1702 Monitor - No Color After Re-capping

Post by rmzalbar »

The way I usually mess up recap jobs is by accidental solder bridges. That's the first thing I would look for, anything I worked on or adjacent to the color circuit.

Depending on what your retrace lines look like, vblank or hblank might be compromised (maybe the point of trouble is common to the signal prior to color and sync processing) or the screen pot on the flyback needs to be adjusted.

I've never worked on a 1702 though. Instead I have jvc tm monitors that are descendents of it.

Could be a faulty or poorly rated capacitor in a critical place:
https://www.electronicsrepairmadeasy.co ... t.html?m=1
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Gyro Gearloose
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Re: Commodore 1702 Monitor - No Color After Re-capping

Post by Gyro Gearloose »

lothian wrote: Tue Apr 04, 2023 6:49 pm I decided to re-cap the thing as the tried-and-true fix all.
Can this myth please die now?
The price one pays for pursuing any profession, or calling, is an intimate knowledge of its ugly side.
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