DrSynth Boss DS-330 : huge noise output since yesterday!

I’ve got an old DrSynth Boss DS-330, which I still like to play with some 25 years after ! THe other day however, all of a sudden, it started to output a very noisy signal, both from the 2 14/inch jack outputs and from the mini jack headset output. I’ve tried to reset it to factory settings, to change cables, etc. Couldnt get rid of the problem. I was wondering whether someone could help me figure what is going on… Seems to me like faulty electronics… But what component? Is there a workaround?

I have been wrestling with the same thing for ages. I finally broke down and bought the service manual and have been going over that to see if there’s any obvious place the noise could be introduced. If I figure anything out, I’ll let you know.