Eminent Omegan 7500 Weird Noise Problem


2020-02-04 1:01 pm
Hello friends, newbie here.

I got old Eminent organ. The pedals don’t work and a few dodgy notes here and there on certain settings. But that's not the main problem. Every few minutes there's this low freq sweeping sine wave appears out of nowhere for a few seconds, followed by white noise hiss and it disappears again. I was about to take this organ to my local chapel. Good thing I discovered this problem before that.
I did the only thing I can, that is disconnected everything that can be easily disconnected.
I came to a conclusion that this anomaly comes from the expression board as you can see in the video there is nothing else left in there, other than the amp.
I dont even know where to begin, what to check. I have a multimeter and a soldering iron, thats about it.
any help, advice would be greatly appreciated.

Imgur: The magic of the Internet
About two years ago I bought an old Hammond Concorde organ. It also makes strange noise immediately when powered on and with no key depressed. I know from issues with PCB contacts that most probably are the cause, but I decided to get it scrapped some day and salavge just the manuals, pedal contacts and drawbar assemblies, perhaps also the speakers.
Best regards!