Wells Gardner K4900 picture offlimits, cant center it. please help

[abispac]

So i got a generic cabinet that came with an snk neogeo system without a cart, and what according to this link https://forums.arcade-museum.com/threads/ms-pacman-restoration-part-3.405826/ looks like an k4900 wells gardner monitor. Now i scraped the neo geo, but before that, i borrowed a cart and tested it. The image looked off limits , as you can see on this image

the credit are outside or as i call it, offlimits, you can also see here

the image its not centered either. Moving the pots dot help much, they are allready either turned all the way up or down and it does not help much. I can shrink the image no problem but either top or bottom would be off limits. Colors are good, but i can see like 3 lines on top that do bother me a bit

I found a couple of  topics about k4900 monitors  but they are not much of help.
Thanks in advance for any help.




 

[grantspain]

just looks badly adjusted to me, horizontal size is via the coil with a plastic hex tool, vertical size on the chassis pot and the screen volts on the flyback is a touch too high
if the picture is not centre then you have the horizontal and vertical position jumpers to help
does not look like anything major to me

[abispac]

Since i dont have a plastic hex tool and actually never seen one, would it be posible to adjust it, while is disconected  to one side, then turn it on , and see the results, ? or does it has to be turned on to actually see some results?

just looks badly adjusted to me, horizontal size is via the coil with a plastic hex tool, vertical size on the chassis pot and the screen volts on the flyback is a touch too high
if the picture is not centre then you have the horizontal and vertical position jumpers to help
does not look like anything major to me

[grantspain]

you need that tool or you will likely fracture the ferrite core, you can buy them from various places
look for width coil adjustment tool

[abispac]

I also found on an old topic from the arcade museum this"

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.

so while i get that tool i also would buy that cap. what do you think?

[Zebidee]

Caps like that are as cheap as woodchips so it can't really hurt.

[Gilrock]

Yes you could adjust with the power off but it could take many iterations.  If you are going to work with CRTs you want to order the plastic tool kit.  They are barely $10.  Checkout maybe arcadeshop.com for one.  Have you tried moving the horizontal raster jumper.  You can see where it is in the photos for the link you posted.  There are 3 pins.  Put it on the one that moves it closest to the direction you need.  I had a CRT where I could not get it to center and someone pointed me to a resistor I could change that would move it over and BAM it worked like a charm so I'm sure there is a way to fix this.  I would do the cap kit first and get the board cleaned up.  I ran my chassis through the dishwasher and it came out sparkly clean.  Then in an oven below 180 F for a few hours.  Those width coils can be fragile.  I've broken one and had to do hot glue surgery to repair it because I could not find a replacement.  Yours looks like a vertical style which might be easier to get if needed.  I would definitely buy that cap suggested in another thread if its not already part of the cap kit you should do.

[abispac]

Yes you could adjust with the power off but it could take many iterations.  If you are going to work with CRTs you want to order the plastic tool kit.  They are barely $10.  Checkout maybe arcadeshop.com for one.  Have you tried moving the horizontal raster jumper.  You can see where it is in the photos for the link you posted.  There are 3 pins.  Put it on the one that moves it closest to the direction you need.  I had a CRT where I could not get it to center and someone pointed me to a resistor I could change that would move it over and BAM it worked like a charm so I'm sure there is a way to fix this.  I would do the cap kit first and get the board cleaned up.  I ran my chassis through the dishwasher and it came out sparkly clean.  Then in an oven below 180 F for a few hours.  Those width coils can be fragile.  I've broken one and had to do hot glue surgery to repair it because I could not find a replacement.  Yours looks like a vertical style which might be easier to get if needed.  I would definitely buy that cap suggested in another thread if its not already part of the cap kit you should do.

Thanks for the advice, yes i tried the jumper to many directions and put it at the far left one as thats the one that helps the most. Tweaked the pots to get the best color i could and i really like the results. It does look like the monitor need either a cap kit or maybe rejuvenating work as is not as bright as i wish but at the same time it looks ok ,it looks good. is just that foldover that bothers me and the fact that i cant get the image to fit the screen. So today im going to unmout the monitor and remove the chassis to but the cap kit here locally. Hope it does help with this little problems.

[abispac]

Update as i still need help with this. So i got me 2 more monitors of the same model. one didnt turn on at all and it has qbert burnt in, so ima scrap the tube. I dont really think ill ever buy a rejuvenator so is trash for me. The second turns on and it has an almost ok image as the horizontal width coil lookd its better adjusted than my original monitor, however it has bad traces on the main board so it sparks alot, also the tube has several old marks of burnt in of diferent games, so ima scrap the tube and use it for parts. Now what i did, i desoldered the horizontal width coil and soldered on my first original monitor, and it helped alot, still not all the way closed as it should be but im getting there. I installed some caps and also did the 3.3 50v cap and it didnt made a diference. So heres where i am now.
Picture 1 shows that the image almost fit in both directions vertical and horizontal. but it is a bit off limits still.
picture number 2, shows 2 or 3 lines of foldover still, still bothers me, i need to find out why is showing them.
Anyway i desoldered the weidth coil in one of the parts chassis, and ima let it rest in cocacola overnight to see if i can get it loose, i know this are no longer made so i dont want to brake it. if sucessfull im replace the one its allready there.
So any advice on what to do to make the screen fit right? any resistors ill should be aware of? Any caps? Or maybe some advice on how to get the weidth coil loose? I really want to keep this monitor, the screen is clean although colors are not as bright as the chinese monitors i have ,is still ok. thanks for any help.

[grantspain]

i can't see any vertical foldover, i can see the screen volts on the flyback is too high and giving you some flyback lines at the top
in any case these chassis will benefit greatly by replacing most if not all the electrolytic capacitors