Hi all,
So I got a Thomson 4123 monitor.
The story of this monitor is that previous owners accidently dropped it from low height.
Nothing major really happed to the outer enclosure nor the CRT itself.
But after opening it I realized that the main board had a couple of cracks, causing trace openings on those areas. So I went ahead and bridged all those damaged traces.
Then, after making a general inspection I saw that lots of solder joints were dry / cracked. So I re-touched all of those soldering issues I could catch.

After another inspection, everything else seemed fine to me so I fired it up.
The image showed up, crisp and colorful, this is really a great monitor.
However, the image isn't totally centered, it hangs up a little.

After searching for this monitor over the net, I found that this monitor is pretty much the same as the Commodore 1901. Actually, it seems like Thomson was the manufacturer of the Commodore 1901 monitor.
There are couple of version for this monitor. The primary difference between them (as far as I could see) are the input interface options. Mine have only db-9 connector, while others have RCA input. It has also SCART input option, that is tricky to use because the pins on the PCB are inverted. There are people that made it fit also.

My main question is, how do I center the image? I couldn't find any potentiometer that is responsible for that. From reading over the net, it looks like it is also an issue for others who own this kind of monitor.

I was able to find the commodore 1901 service manual that includes schematics. It looks like that main board of the Thomson is similar to the Commodore, but the daughter board (the vertical one, who sticks to the main board) is a bit different.

Any option to modify the boards and add a potentiometer that will control the image vertical position?

You can download the Commodore 1901 service manual here:
https://gona.mactar.hu/Commodore/monitor/sche … igh_Quality.pdf

Thanks.