Looking for a schematic of a Shure Beta 87 A

I have a Shure Beta 87 A that produces a very low output level and a lot of noise.
The owner said that he has dropped the microphone.
One would of course not expect that electronic components have failed because of the drop.
When I inject a signal at the gate of the FET, I get a strong signal after the FET.
But after the 2 transistors, the level drops.
Also distortion sets in at fairly low levels when connected to a phantom powered microphone input.
Frequency response is reasonably flat, but drops below 100 Hz.
Transformer seems to be OK.
Because it is a pretty cramped double sided PCB, it is a bit difficult to trace the schematic.
I have searched this board, but appearently no schematic is available? Or am I wrong?...

I didn't found any schematic or service manual for it, and i've searched also few times in the past.
You can't also count on shure customer service help...
I found similar symptoms in sennheiser 614 electret.