Hey guys, first time posting in this subforum, thanks for all your help

I've been trying to set up this monitor for a while now. At first, I tried hooking it up (after mounting it to that wooden case) to my 15khz capable PC, which is known to be working good. No sync at all, scrambled picture... Ok, I thought, maybe I need to do a fresh install of CRT_Emudriver and Groovymame to get this to work? Anyway, I left this at my bedroom.
Last week, I started messing around with it, this time with my Neogeo 1slot mobo, and same issue. Scrambled picture, at first it stayed like the video shows but then started moving, like when you are having H.Hold issues.
I've tested with two good jamma harnesses, and I made sure to be plugging the connector right (it uses a 5 pin connector, RGB-Gnd-Sync).
It's a 19" tube with a no name chassis, I think it's Eygo or one of those, because I have several of the same chassis (same component location, etc) but with different board colors and pot labels (for example, in the video I'm messing with V-Hold if I remember correctly, and it makes the picture start rolling as you can see. I also found a pot in the chassis facing the tube which controls the 'other' Hold, but still no luck, no sync at all.
Sorry, I don't know how to make the preview visible inside the post
So, messing with pots makes no difference, cables are good, and I've tried with both a Jamma source and a 15khz PC video signal.
Is there something in the chassis that can go bad and cause this to happen? Hopefully, a reflow / resoldering can help, but I can only take a look at this in the nights after work
Thank you all guys