maclean wrote:Usually I put the ground through the hole on the heatsink of the chip on the I/O board, however in this case I tried several ground points including the left side of r144 which according to the schematic is a ground... No matter which ground, I got a consistent result.
OK. I'm only asking because there are actually different "grounds" (an analog and a digital one) that are tied together on the IOboard. If both J3 and J4 are connected they behave as one "big" ground; if either J3 or J4 are connected (but not both) they don't which can lead to strange things.
maclean wrote:I have removed Q37 and as you said, the middle pad is measuring about 11.7v close enough I believe?... Again not going to take any further action till I hear your thoughts.
This looks as if (at least) Q37 is faulty. If you have a spare SC536 install it. If you don't have a spare you can use Q50 from the IOboard in the meantime (you'll not have any MIDI In functionality without Q50, though).