I have a 520 ST+ (no F, no M) and I have a problem with the video (I think).
When I power it on I get GEM desktop and all seems to work OK but the screen goes black for a split second every now and then (irregular/no pattern - can be OK for a minute and then go black or can be 10 seconds and black). It doesn't look like it's affecting the Atari (ie. everything seems to work) but it's very annoying... I'm using good quality rgb scart that works with my STE.
Any idea where to start looking for the solution? I've tested/replace power supply, I changed video cable, my TV works perfectly fine with my other STE...