Video Issues in Two 29" CRT Monitors. Chasis pictures and video of the issues

[Guepardo]

Hello everyone.
I have built two arcade cabs from scratch around 2014. Basically I replaced the CRT and its chasis with new ones, did several cosmetic modifications, did my own control panels based on usb gamepads. The two systems were a PC with Groovy Arcade to convert VGA to CGA.
Last year I bought two GBS-8100 boards to do the VGA to CGA conversion by hardware, upgraded the computer hardware and now I run both machines with Windows 10 and RetroFE.

I don't know the brand of the CRT, these are 29 inches and the chasis are from EAGO.

I'm having an annoying video issue from the beginning. Most of the time the video is fine, but sometimes I have a flag effect, the left and right sides of the screen start to move in a wave pattern. The waves usually are very small, and they just are on the sides. Sometimes they propagate to the whole screen. But since they are small the video its still acceptable. The size of these ondulations might increase from time to time.
Another video issue I have sometimes is the left and right sides of the screen start to shrink to the center, expanding and shrinking around one inch.

I've found some articles in the web relating these issues to some capacitors failing. But these issues are present in two separate machines, so I think the problem is in another place.

Here in Argentina we have 220V AC line. The cabs are two OK BABY ones with a 220V Isolation transformer, and a 220V to 110V transformer for the monitor. Maybe I need an AC stabilizer?. Or an AC filter?.

I have a 29 inches CRT flat screen TV in the same room and it doesn't have any video issue. All the home appliances work fine except for this occasional video issue in the arcade monitors.

Maybe my ground wire needs to be replaced?.

When I bought the monitors the seller said they were new. They tested them with me at his place and the video was perfect. Maybe these hardware is not new, but "new old stock", with several years since its manufacturing?.

I really don't want to dissasemble the monitors, these CRTs are very heavy, but sadly to access the chasis I need to extract the whole monitor out of the cabs. But I fear that the monitors can be damaged if I don't solve these issues.

I'll really appreciate if you can help me solve this.

Thanks in advance .

[Guepardo]

Here's some pictures of the chasis:

The only data in the chasis:


Board:







Potentiometers:







A picture of the screen showing some white lines at the bottom. They dissapear if I low the brightness, but I tuned it to the lowest possible value. Otherwise the image is too dark.
You can see a "shadow" vertical line at the left margin. It seems to be related to the GBS-8100 board.



And here is a video of the two mentiones issues:



Thanks in advance.

[grantspain]

screen volts too high on flyback

[Guepardo]

screen volts too high on flyback

Hello, Grantspain.
Thanks for your reply.
So it seems an easy fix, I just need to tune the "screen" pot of the flyback, right?.
Regards .

[grantspain]

yes, then if your picture is not bright enough use the gain pots on the gbs converter

[Guepardo]

yes, then if your picture is not bright enough use the gain pots on the gbs converter

Perfect, thanks a lot.
I will do it right now.
Have a great week.

[Guepardo]

Well I adjusted both flybacks, "screen" pots.

Here's the results:

Arcade Cab A:



Arcade Cab B:



The picture got darker, but the image quality seems to be much better, with more brilliant colors.

Fortunatelly I didn't need to adjust brightness, since the GBS-8100 doesn't have any pot to do that. All settings are modified through an OSD menu and changes are lost once power is shut off.

About this clearer vertical line in the left margin of the screen (old pic before adjusting the flyback):



Its present since I switch on the cab, before I switch on the computer. Should I worry about it?. Most of the time its not visible, but I wonder why it has appeared.

Regards .

[Guepardo]

Hello everybody!.


Well, recently I made some modifications in the cabs, and I wanted to share them. Maybe they can be useful to anyone with similar problems.


The first thing I did was adding an AC stabilizer before the transformer of the cab. This transformer only feeds the CRT. All the other devices are connected directly to 220V.

I've been investigating, and my 29" CRT monitor should consume around 150W. The stabilizer has a peak power of 500 VA and a nominal one of 240 VA. Thats around 160/170W so it suffices perfectly fine.


After I adjusted the "Screen" pot of the flyback the video issues almost dissapeared. I rare ocassions I had a minor flag issue.

But, when the air-conditioning was in use the video issues were much worse. Obviously, its great power demand caused low voltage.

Now with the stabilizer all these problems are solved. I also notice a better picture.


The second change was to modifiy the switch 3 of the GBS-8100 labeled "size".

This switch is not mentioned in the manual. It reduced the image size on the screen a little, and I had to adjust the image again with the chassis controls.


Now the mentioned "line" is almost invisible. Is most noticeable with dark backgrounds, but at least is mostly gone.


Regards .