How can I fix this poor display quality?

Hi,

I recently received an old Samsung SyncMaster 2243SN that didn't worked anymore. For a couple of € I replaced the capacitors and made it work again but the displayed quality is very poor. Does someone know what the issue is? I have this big pixels on the screen and an effect called “burned faces" (?).

What I tried:

• Change the connected laptop -> same issue
• Reset the settings of the screen -> same issue