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I think this isn't the best place to ask a question like this, but I tried some tips I found on other forums and none worked.

My CRT TV is acting weird... it has horizontal retrace lines only on the center of the screen.
If I play a bit with the screen adjust on the Flyback I get them to disappear, but the screen becomes too dark.
If I turn the screen adjust to the other side, they become fullscreen.

Any tips or other forum recomendations are welcome.
Thanks in advance!

To make sure I understand ... you can see the electron beam during horizontal retrace but only in the center of the screen?

This is almost certainly a bit of crosstalk between all the HV parts of the tube, one of the more awkward bits to compensate for. I don't know what to look for, but I'd start by seeing whether I could get my hands on the service manual for the TV.

If the TV was made in the late 90's through early 00's, I would be extra suspicious of any electrolytic capacitors.

edit: https://en.wikipedia.org/wiki/Capacitor_plague

What kind of TV is it exactly ?

It kind of sounds like black current loop isn't working right, so the video amp might be damaged or there might just be a bad connection. Did it happen suddenly ?

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http://www.tmeeco.eu

I hope this picture helps to explain better:

It had a problem that it had sound but no image.
I tried to activate the insurance and they "fixed" it.
Unfortunately they say it has no problem and that are "my eyes" that are seeing something that doesn't exists.
Did I somehow become a medium or a prophet to see more than meets the eye??
I'll try to get the service manual and look for bad caps and resistors on the circuits surrounding the tube.
Unfortunatelly the label that has it's model number is missing but I bought it new around 2008.
And... yes, it's a CCE!!

If it is a capacitor problem it only involves one or two high voltage capacitors that are on B+ (usually +140V) and Video Supply (usually +200V). Service manual will list the exact voltages if you can find it, and when you do, I'd like to take a look also.
Low filament voltage can have such effect too, acceleration voltage (the thing you adjusted on the flyback) needs to be boosted to gain brightness, but sooner or later you reach cutoff limit and guns don't get switched off at low/no signal levels (reason you see the retrace lines).
If all those voltages check out then the tube is EOL. You can do a trick that boosts filament voltage (more heat, more electrons, more brightness) but it will only postpone the inevitable a bit. Flyback itself might be bad too, if anode voltage drops so will brightness but you cannot really measure the anode voltage (15...28kV, depending on tube size).

_________________
http://www.tmeeco.eu

Given the spacing there, that actually looks like it's leaving the gun on during vertical retrace... makes me suspect that it's never actually turning off the guns at all.

horizontal blanking retrace lines are pretty much invisible due to their speed, the ones seen on the photo are indeed of vertical blanking period.

_________________
http://www.tmeeco.eu

Retrace lines are invisible because they occur during the horizontal and vertical blanking periods of the video signal. During both horizontal and vertical blanking, the voltage is set to the blanking level, which is below the black level (outside of Japan at least), and this is done to make sure the gun does not output during retrace.

Modern TVs may manually turn off the gun during retrace, but "officially", it's the video signal that's supposed to turn off the gun during the retrace.

I've seen a TV before which has these lines when you're sitting on the blank input screen with no signal, but the lines disappear once an input signal actually appears. Do you still see these lines when you have a device plugged into the TV and turned on?

Yes I do.
They're less noticeable on scenes with lighter colours and very apparent on dark.
I'm just kind of pissed off because it seems the guys who fixed it removed the identification label, besides saying they're seeing nothing.
Would this be very noticeable to me because I'm a old gamer or it's just an excuse to not fix not completely well done job?

I'm still searching for some service manual. Looks like I've put this TV name on my (very messy) Xorg.conf:

If someone is interested in see the full mess, the file is here. It's a multiseat setup, what kind of explains the mess...
Unfortunately I could not find anything besides the remote control and its LIRC codes.

Yeah, something's really funky, those lines showing up suggests that the brightness is set so high that the blanking level is above 0 volts, but for that to happen, the picture would appear really super light and washed out, so something else must be wrong.

It's not automatic gain control copy protection, is it? Because when I was in school, I saw a cheap TV where that caused distracting white lines across the screen to slowly fade on and off.

Interesting.
But it seems to not be the case since this picture was taken with no active video source.
I strongly need to take my time and disassemble it.
Maybe I can at least figure the correct model number.

That sounds like Macrovision protection on a DVD, combined with a cheap television that has harsh overscan and/or doesn't blank during vertical retrace. Those were intended to upset consumer-grade VCRs, which might encounter tracking problems when the white lines are introduced.



It does look to me like your Screen /G2 control is too high. If there are bias controls for the individual guns, you can try turning those up after turning down the screen control on the flyback to counter the crushed dark colors that you'd get from turning down screen.

I'm dumb when it comes to electronics, but have you inspected the area that was repaired for shorts? Maybe they screwed something up when they fixed it.