Having a Vertical Linearity issue...

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PacManPlus
Posts: 28
Joined: Sun Apr 03, 2022 9:40 pm
Location: Central Florida, USA

Having a Vertical Linearity issue...

Post by PacManPlus »

Hello -

I was hoping someone could help here. I've purchased two of these: https://www.ebay.com/itm/116772811350
However they do not come with the remote boards. They seem to work well, and the seller was great.

I noticed that the boards had a place for Variable Resistors instead of the remote board, and I had a bunch of spare '103's (10k) hanging around, so I put them to use... and I got a picture! (I'm testing it with a standard Pac-Man board).
However, the screen seems to be compressed on the right side. I've included pictures below.
I'm *guessing* that I need a different value of Variable Resistor in the 'V.LINE' place (second in from the left). But I've tried different values for that resistor and nothing seems to help.

I've tried *both* boards, trying to narrow the issue down, but they both do the same thing. I've also tried two tubes, and *they* both do the same thing... so I'm stumped.

In the second picture below you can see how the maze is squished on the right side.
Does anyone have an idea of what to try?

Image
Image
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PacManPlus
Posts: 28
Joined: Sun Apr 03, 2022 9:40 pm
Location: Central Florida, USA

Re: Having a Vertical Linearity issue...

Post by PacManPlus »

BUMP - Apologies, but I was really hoping someone could hopefully give me a direction to go in. I don't mean to bug, I've just got everything open on my workbench (please).

Thank you so much...
KPackratt2k
Posts: 280
Joined: Sun Apr 04, 2021 11:02 pm
Location: Seattle, WA, USA

Re: Having a Vertical Linearity issue...

Post by KPackratt2k »

If you have access to an in-circuit capacitor ESR meter, it may be worth a shot to check the ESR on the capacitors for the linearity circuit to make sure none of them have high ESR.

If the chassis has a linearity coil, try adjusting that with a plastic screw driver.
MKL
Posts: 453
Joined: Wed Feb 02, 2005 9:33 pm
Location: Pordenone, Italy

Re: Having a Vertical Linearity issue...

Post by MKL »

Check if your chassis follows these schematics, at least the part that is relevant for linearity:
https://ibb.co/tTjyGZCZ

Here the trimmer is 5K but if it's used as variable resistor (wiper = one of the other pins) I don't see how it could do what a 10K (103) doesn't. A 10K would just be more sensitive to movement. Rather, I would change the resistors in series with the trimmer, those corresponding to R414 and R413.
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PacManPlus
Posts: 28
Joined: Sun Apr 03, 2022 9:40 pm
Location: Central Florida, USA

Re: Having a Vertical Linearity issue...

Post by PacManPlus »

Thank you both for the reply; work has been taking up most of my time but I am going to see what I can figure out.
There is no adjustable linearity coil that I can see; just the pot adjustment that I had to put in (you can see it in the picture).
I'll also look for the resistors in line with the trimmer.
Worst case scenario, I'll post a full shot of the board to see if anyone sees anything obvious.

...at the same time, I'm trying to work on a Baby Pac-Man VIDIOT board that's only giving me two flashes, and I've already done the troubleshooting I've found on the web... So I'm having all sorts of issues :P

Thank you!
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