k4900 foldover

hindered

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I've got a k4900 with some foldover on the left side when mounted vertically (top when mounted horizontally). I ordered a cap kit from Mr Bob Roberts, and noticed that a couple of my caps didn't match his (C313 or whatever it is was 47uf instead of the 100uf provided, and one 3.3uf cap instead of 2.2uf). I went ahead and installed the new caps anyway, and the foldover got much worse. I went ahead and reinstalled the original caps for the two positions in question and was back to my original display: good color, good geometry, good width and height, but foldover on the left side.

Any ideas how to fix this?

Also, I've got the older model chassis that has a jumper for "fine tuning" the centering.. even though I have the horizontal one as far "down" as it'll go, I can't center my image vertically. There's probably an inch of black to the right and the image is flush with the left border. Any way to address this?
 
Here's some pics, a couple of the chassis and one of the foldover. The chassis pics are pre-cap-kit, and the tube image is post-cap-kit with the two incorrect value caps installed. The image looks like that now still after reverting to the old caps for those two positions, but the area folded over is much smaller. In my infinite wisdom, I didn't take pics of the monitor after reverting the two caps.
 

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First off, that's not really foldover. if it were foldover, you wouldn't see anything past the lines.

Second, your vertical size is too big. Adjust it down so that you can see the entire screen. Once it gets a bit smaller, you might not see it as much.

Third, was this chassis always with this tube? You're missing a vertical Dampering pot on your chassis. Usually this means you have an early model K4900. You can tell because the number silk-screened on the back will end with -023. If it does, then it means the chassis must be used with a specific yoke. If this chassis has always been with this tube, then you're probably okay. It it has not, then you might have a mismatched set.

Fourth, sometimes I see this when using these chassis with the multicade boards. Most of the time you can adjust it so you only see it on the very edge of the menu screen, but then you never see it during game play. You may not see it if using it with a normal board.

And the caps you mentioned - C313 should be 100uF 160v, and C303/C308 should both be 2.2uF 50v...
 
First off, that's not really foldover. if it were foldover, you wouldn't see anything past the lines.

Second, your vertical size is too big. Adjust it down so that you can see the entire screen. Once it gets a bit smaller, you might not see it as much.

Third, was this chassis always with this tube? You're missing a vertical Dampering pot on your chassis. Usually this means you have an early model K4900. You can tell because the number silk-screened on the back will end with -023. If it does, then it means the chassis must be used with a specific yoke. If this chassis has always been with this tube, then you're probably okay. It it has not, then you might have a mismatched set.

Fourth, sometimes I see this when using these chassis with the multicade boards. Most of the time you can adjust it so you only see it on the very edge of the menu screen, but then you never see it during game play. You may not see it if using it with a normal board.

And the caps you mentioned - C313 should be 100uF 160v, and C303/C308 should both be 2.2uF 50v...

Thanks for the reply -- some points:

First: Thanks for the clarification and education.

Second: I have adjusted it down since taking that picture -- your'e right, it was way too wide. Problem still exists.

Third: I'm not sure, although I've seen other posts indicating this as a possible issue. I'll have to investigate further.

Fourth: You're right, I was able to get it to the point where it was only visible on the menu, and not an issue during gameplay. Problem still exists on a different JAMMA board.

Fifth: Please see http://forums.klov.com/showthread.php?t=111159 and http://forums.klov.com/showthread.php?t=48027 with regards to C313. The problem became much worse and was unadjustable to an acceptable point with 100uf in C313.
 
sometimes the ceramic capacitor that is connected to the horizontal output coil needs to be changed to accomodate the swap. It is a big orangeish red cap. Its size determines the Horizontal range of adjustment(up and down view in a vertically mounted monitor). Bob roberts has an article on the specifics. You might have to move the yellow wire from post to post to then adjust the vertical shift (left and right in vertically mounted monitor).
 
I'll be watching. I have the same issue. Early 4900 mounted vertically with a 60 in 1. Adjusted to minimize the problem and just left it that way. Sure would be nice to get it fixed.

Murph
 
I have found and scanned the Wells-Gardner service bulletin about the 4900 series foldover with the yoke/chassis mismatching.

It is now available as a pdf file at Michael Roma's website.
 
I have found and scanned the Wells-Gardner service bulletin about the 4900 series foldover with the yoke/chassis mismatching.

It is now available as a pdf file at Michael Roma's website.

Thanks for the information. I still need to pull this out and investigate the yoke/chassis combo.
 
Rise from your grave!

I know this is a thread resurrection, but did you ever get it fixed. I have exactly the same problem (early 4900, multicade board). The thing I found is that, even though the caps that Bob sent me matched the drawing, they didn't match the parts list.
 

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I am still having the same issue with a different k4900 in a Sinistar and the K4900 monitor with the original yoke and tube. It has been re-capped in the last 6 months.

Weird. I'll take a look at the cap values.
 
Link no longer works, but is it just a given that the lines are there with a 60/1 board? I can't adjust it out.

all that stuff got moved to
https://sites.google.com/site/mtpacifico/kens_korner

pretty sure that you are stuck with it if the monitor is displaying that problem with a multiboard, but the only time i ever had that issue we just swapped to a different monitor and kept on going. didn't try swapping caps values or coils or any other mods.
 
To revive this thread since it's one of the first results when you google this issue...

I've had a WG4900 in my Robotron for years, with the same chassis as pictured in the images in this thread, that exhibited the same issue also pictured in the thread. So, as you typically do with monitors, you recap them when there are issues like this. I did this about 5 years ago, and installing the cap kit didn't help at all.

Today I decided to finally tackle this problem.

Looking through my filing cabinet, I found two separate cap kit instructions for WG4900; one from Zanen, and one from some unknown source, but both list C308 as 2.2uf / 50V capacitors.

However, digging through my WG4900 schematics, I found one version of the schematics where C308 is listed as a 3.3uf / 50V capacitor instead.

Willing to try anything at this point, I swapped in a 3.3uf / 50V at C308 and the picture is now perfect! No lines wrapping over at all, and picture fills full screen.

So, there you go; if you just recapped your WG4900 with a capkit and you have vertical fold over, you may have a chassis that requires a 3.3uf /50V at C308 instead.
 
this has come up but its only on one certain model of k4900 and super uncommon but i can't remember specifically which one but there are a couple recent threads about it.
 
To revive this thread since it's one of the first results when you google this issue...

... So, there you go; if you just recapped your WG4900 with a capkit and you have vertical fold over, you may have a chassis that requires a 3.3uf /50V at C308 instead.

Cool. Thanks very much for posting this. My Stargate monitor has this issue. I will install a 3.3µF cap at C308 and see what happens.
 
OK. Good news and bad news.

First, here are some pictures of this monitor before changing C308. The image on the left shows the vertical size set very small to avoid the foldover at the top. The image on the right shows the foldover when I set the vert size to fill the screen.

uc

https://drive.google.com/file/d/1ep5TTRZdEnbuqzBH05c0QzzmjrRIQnhC/view?usp=sharing

I did not have a spare 3.3µF, 50V al cap lying around. But, I did have three 2.2µF, 250V film caps in my junk box. By putting 2 of these in series, then putting them in parallel with the third cap, I was able to get 3.3µF.

The image on the left below shows the 2.2µF, 50V cap I had installed when I re-capped the monitor. The image on the right shows the new 3.3µF film cap assembly. Looks pretty goofy. But, I already have a hand wound horizontal width coil installed, so this chassis looks weird anyway.

uc

https://drive.google.com/file/d/1AFdQxxKl8mor_TFaaQeGBMDPXf4WsT4O/view?usp=sharing

Good news! The foldover is gone. I can now adjust the size to fill the screen. My linearity is better on top too (still squashed at the bottom tho).

uc

https://drive.google.com/file/d/1yMdbiE_AFks8oJ5i3ovvlzepVj_817AT/view?usp=sharing

This mod works. It would be better if I just had a 3.3µF, 50V cap, but this is fine.

I just re-capped a different 4900 for someone a few weeks ago, and I did not see this foldover problem. So, does not affect all 4900s.

Bad news: My Stargate went flatline a month ago and I haven't been able to fix it yet (even the ROM board LED display is dark), so I can't play it and enjoy this improved image. Looking forward to getting it back running.

Many thanks to mjenison for the tip.
 
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Just wanted to bump this thread as I was only able to fill 2/3s of a screen without being severely affected by fold over. Replacing C308 with a 3.3uf cap vs. the 2.2uf fixed it. I now have a full screen.

6439B493-2BF2-4213-960E-C37C609AF24B.jpeg
 
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