520STFM RGB Out SCART Audio Buzzing & Display Fuzz

[lzappa]

I've used the RGB out for the first time today, via one of the following SCART cables from Retro Computer Shack (apparently very reputable):

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I'm experiencing quite a loud continuous buzzing noise through the audio, which can change in pitch depending on what kind of load the ST is under. I've not fired up this ST for years and I don't have a composite cable to hand to test it via the other non-RGB port.

https://www.youtube.com/watch?v=4MdwI9xaCj4

As you can see from my video, the display can be very crisp clear momentarily when wiggling the cable connector in the port but soon goes back to being fuzzy. It may be hard to tell in the video but the green desktop goes from being a completely clean flat colour to having little zig-zag lines through it.
When the ST makes plays any sound, for example when pressing the keys at desktop, you can hear that the buzzing goes away completely and then slowly fades back in again.

I've heard about people recapping the PSU's to fix certain problems but I have no idea if that applies here. I opened it up to see if anything stood out but I couldn't see signs of dry joints or anything like that. It looks like there may have sat on top of a minor spill at some point in it's life, which you can see from the small brown marks (these rub off with my finger) unless this is just old flux perhaps:

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Old dry flux on the surface?

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No real signs of liquid damage anywhere here.

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[exxos]

Recap PSU.. Resolder rgb port.. Clean it with contact cleaner...

[czietz]

I had the same symptoms with a ST-to-SCART cable: buzzing audio and bad image quality and it turned out just to be bad contacts. Thus, using a contact cleaner on the video port (as proposed by Exxos) should be the first step.

[lzappa]

Thanks guys. I'll let you know how I get on.