ON561 problem.
The problem with the ON561 seems to pop up at a regular rate.
I must admit that I didn't pay much attention to it because I didn't
understand what the problem was and I still don't. If you got a
defective ON561 there's gonna be also a good half which can be
used to select another fet to replace it. So build part of the circuit
from the scope twice on a breadboard and start comparing the
original part with a number of lookalikes which you select from the
Philips program. Possible candidates are BFW10, BFW11 and 2N3823.
But most of these will be obsolete so see what is still available
from other manufacturers.
The description of the ON561 by Panter did ring a bell, I started
digging and I found two similar double fets, the ON235 and the
ON384 which had it's terminals shorted by conductive straps.
I also found similar double fets in a databook of 1976, the BFS21
and the BFS21A. Probably also obsolete.
I'm afraid this post won't be of much help.
So build the test circuit and start comparing what is still available.
on1aag.