[sdiy] Korg Delta problem

[Jean Bender]

Hi !
i just got a korg delta, but it seems to be a bit tired.
Once you start it, it works as a charm, no probs, but if you wait one,
two hours, even if you are outside, with sun or no, the synthetizer
part stops by itself.
All four voices shut down, but i still can use the string part.

It looks a lot to me as a temperature problem, but if i open it,
nothing seems to be broken or something.

Where should i look at first ? Would it be a cap problem in the audio path ?

Any help would be greatly appreciated.
Thanks !!
J.