Hi Forum

I have a set of Beolab Penta's 2.nd generation, which have developed a fault in both units.

I feed them by the RCA input and they turn on fine when signal is applied, but they are playing with a quite low volume.

The "funny" part is, that if I move the mode switch (off-auto-L-R) from auto to off, the volumen turns loud at normal level for a fraction of a second. Switching back to auto it plays again with low volumen. 

If I move the switch after app. 10 minutes ON time, it will suddenly play fine at the correct volumen level.

I have done a range of measurements. All supply voltages are fine and smooth. Tracing the signal with a scope, show that the signal is weak all way through the amplifier, even at the RCA input.

So, something is "clamping" the signal. The level switch is working fine in 3 steps, and so is the bass level switch. Even though, I tried to disable them by desoldering PCB 7, but then the signal turned extremely high, and the amp went to "yellow lamp" (soft clipping?) mode, and had to be restarted.

Anyone having a clue? Or a circuit description?