Originally Posted by Forte
It is probably Q3P (MPSA42) that is causing the low reading on Pin 6 and D1R, I had a similar problem with low voltage(55v) on Pin 1 and D1L, replacing Q4P fixed it.
It would be fairly easy to test, though with a steady voltage drop across it, I'm not sure.
Anyhow, with the amp turned off, set your DMM to diode test. Put the red probe on the base (middle pin). Put the black probe on each other leg (collector and emitter). It should measure about 0.6V for both. Reversing the probes should yield nothing.
An NPN can be viewed as two diodes, back to back, for this test. With the anode at the base and the cathodes at C and E.
If it passes, the transistor is good.
You can do a similar test for the CRD, i.e., one way only.