Trace Elliot RAH600SMX low output level problem

Since a while I have been tinkering with my RAH600SMX to get it working again. The problem is that is seems to be working fine but at a very low level. When I connect to an active bass and crank the gain up all the way I manage to get the green an yellow light to light up. I would expect it to go full in clipping, especially since the bass has very high output level.

I have found the schematics and have been debugging for quite a while now and come up with the following findings.

Turning the input blend from FET to Valve (and back) makes no difference, since there are separate circuits and assume that those parts are fine.
Enabling/disabling the Pre-Shapes also make not difference, so since these are also separated signals paths I again assume that these parts are OK
Same goes for the EQ section.
I tried bypassing the Compressor section by using a patch cable between Send from FX1 to the return of FX2. Same problem. So seems not to be a problem over there.
The full range outputs connectors can also be used as inputs in seems are there are directly connected (through a Pot) the end stages. Connecting a mixer to them an giving them signals makes the room shake so the end stages also seem to be fine.
Since the gain LEDs are connected somewhere in the EQ circuit and they indicate the low level a assume the problem somewhere to be in the first part of the circuit around the input gain stage.

Now my questions
Is there anyone out there who had the same problem or has experience in fixing these amps?
If so any ideas what the problem might be?

Thanks a lot for any help.

Kind regards,
Peter

 

Would consider bringing it to a expert, but since I live in Switzerland the transport costs to the US and back would probably buy me a new amp.

 

Thanks. I tried that yesterday. Resoldered half the board, but no go.

Also connected a 100Hz tone generator with 1V peak-peak as suggested in the drawing an measured all the reference points. Everything seems to check out and the yellow light lights with the test signal.

I also measured the input impedance and it is also Ok. But when I connect a bass I get about -12 dB signal max out of the FX1 send. Any ideas?
Does anyone know a board where some TE fans/techies hang out?

 

Thanks, but I tried a passive bass and a brand new active bass which gives a lot of output on my other amp.

 

Yes is it and switching on/off eq or preshapes does not matter. Also moving from FET to Valve does not matter so is assume the problem is also not in those parts of the circuit. That leave very little left. Only the buffer stages between those different parts, but from what I was able to measure all seems to be fine.

This think is driving me crazy