Hello,

I purchased a used Sony CPD-G400, and it's in relatively good condition (except for slight screen burn-in in the center).

After about a week of normal use without any noticeable problems, the monitor suddenly went majorly out of focus (so much that it hurt to look at the screen). This would happen after the monitor had been running for at least an hour or so. Most of the time, if I let it keep running, there will be a loud spark/snap sound and the monitor will suddenly go back into focus. Other times, the monitor doesn't go back into focus after a minute or two, so I shut off the monitor for a few seconds and turn it back on, and it goes back into focus.

Does anyone know what the problem could be, and if I can do anything to fix it? I was suspecting it was a faulty connection or a short that happens after it warms up, and letting it cool slightly allows it to go back into place. I've tried putting the monitor on its face and hitting the sides to see if I could loosen any short-causing debris, and it seems like it's going out of focus less frequently now, but it still happens at least once a day.

Also, while the monitor is warming up, any horizontal black lines seem to have a grey "twin" right below it, which is pretty annoying. It seems to mostly go away after about half an hour (the usual warm-up time), but I was wondering if there's any way to fix that too.

Thanks so much in advance!

Sounds like a CRT fault - seems common in these and the 21" G500/520.
However it can also be caused by the line output transformer or the CRT base connections but in my experience its always been the CRT.

check the connection betwen focus output of fbt and crt, can be loosen

He encontrado que en ciertas ocasiones el socket del CRT se contamina de impurezas y dentro de el en los arqueadores (spark gaps) ocurren fugas continuas de corriente. Debera desensamblar dicho socket y limpiar por dentro dichos arqueadores. Tambien tenga en cuanta limpiar la zona de conexion del G1 al CRT (chupon). Si su problema no es el CRT entonces habra encontrado la solucion a su falla. Suerte.