WG4900 horizontal color misalignment

mike944

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Hi everybody, i'm new here. I have a Baby Pacman with a WG4900 monitor. sorry for the long message, i'll try to describe it as best i can. I'll follow up with some pictures.

I just recapped it, and reassembled it. while trying to readjust everything, i noticed what appears to be a horizontal offset between the various colors. i don't remember whether it was there before the recap or not, but i think it was. Note: The monitor is 90deg to the normal orientation, but all my comments are referring to monitor directions, and ignore the fact that it's oriented sideways. When i say left, i mean monitor left. (the left-side is mounted towards the top)

I'm pretty sure the problem lies in the drive electronics, not the adjustments on the picture tube. I've moved just about every adjustment, and it doesn't seem to help or hurt anything.

I also messed with all the on-board horiz adjustments, and i can't seem to make it any better or worse.

Unfortunately, i don't have a signal generator, all i have is an oscilloscope, the color bar screen courtesy of the Bally video controller, and the horizontal line you can get by tying TP302 to ground. Unfortunately, since the problem is horizontal, the horizontal line doesn't help much. (is there a built-in vertical line?)

Using the color bars, and turning the screen control way down, i can get the problem to clearly appear as vertical colored lines on the right-hand side when there are vertical transitions between the black background and each color.

I went through the white balance adjustment on P7 of the WG 4900 manual, and i noticed that the line in step 5.6 sort-of "fades in" on the left side, and the right side has a "hot spot". Same thing when i remove the jumper and view the grey raster. the left side "fades-in" and the right side has a bold line.

Any ideas?

Thanks,
Mike
 
Last edited:
Here's the pictures i promised.

With the screen set normally, this issue is not too bold. in the images below, I've purposely adjusted the monitor to illustrate the problem, and make it look it's worst.

The first picture is during the white-balance adjustment procedure, with TP302 tied to ground (TP301). Notice how the line gets a bright spot at the right-hand end.

http://i129.photobucket.com/albums/p205/mark129845/IMG_1239.jpg

The second photo is also during the white-balance adjustment procedure, with the jumper removed, and the screen control turned up just enough for a even grey screen. Note the whole right-hand edge has a bright line.

http://i129.photobucket.com/albums/p205/mark129845/IMG_1238.jpg

The 3rd photo is of the Bally color bar screen, with the screen control turned way down to make this anomaly appear as best i can. As you can see, colored lines seem to appear at any place where a black background turns into a color (looking left to right, not sure which direction the scan happens) it does not appear where colors change from one color to another. It's like the colors don't all shut off at the same time. Like the red and green stay on a fraction longer then they're supposed to be on for, instead of shutting off at the same time. Not sure any of that makes any sense.

http://i129.photobucket.com/albums/p205/mark129845/IMG_1242.jpg
 
Do you have a game? Hook it up to a classic game and let's see what it looks like....
 
Yeah, it's in a working baby pacman. The game is definitely playable, but after doing the cap kit, i was basically expecting the picture to look almost new (except for the small amount of screen burn)

The distortion is bugging me. I'm pretty much ignoring the game at this point, because it's much easier to see the problem during the monitor adjustment and color bar setup.

You can see the color distortion anywhere there is a black line on the left, followed by a colored line on the right. the easiest place to see it is about 2 "pac-man widths" to the left (or above) of pacman in this view. See how there is a bright vertical green line on the left edge of the green field? You can also see it on the red escape tunnels

http://i129.photobucket.com/albums/p205/mark129845/IMG_1243.jpg
 
Have you tried replacing the IC on the chassis? It might be overdriving slightly giving you this odd effect...
 
I haven't replaced anything other than the cap kit.

i did notice that the cap kit had 3 caps that didn't match the caps either on the board, or in the manual. the new C308 was 2.2mf. What i took out (and what the manual says) is 3.3mf. The new C311 was 4.7mf, the old one (and manual) was 10mf. C313 new one was 100mf, the old one was 47mf. Could any of those cap differences cause the issue?

I can try replacing the IC. I have a o'scope, is there anything i can check for, before replacing the chip?

What exactly does the IC do? I couldn't find a datasheet in english.
 
I just figured out i have a 4800 monitor, not a 4900. The cap kits are different for the 4800 and 4900. I installed the 4900 kit, because that's what i thought i had. Does anyone know what the difference in kits is? is it the components i mentioned above? None look like they have anything to do with the horizontal circuit, but i'll try changing them and see if that fixes the issue.

Anyone have a manual for a 4800 monitor? i couldn't find one online anywhere. I did find a schematic, but not a manual.
 
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