Wanging everything with engraving tool + nylon bolt eventually elucidated.
Loss of ch 2 , no prob on its i/p board, due to bad mono/stereo/bridge slide
sw on the ch1 i/p board.
Unusual DC rails for the SMD opamps , will go on my tips files for anyone
else confused by this.
One operates from -113V and -101V supplies and the other 40V and 55V, same
for both ch