You can verify the preamp by using headphones to test, can't hurt to verify bias as well.
Haven't done any work to my 2285 except rebuilding the power supply so can't comment further on your issue.
I used my multimeter on diode function to measure the transistors. I'm not exactly sure how to read these.
Transistor measurements are as follows while in circuit:
2SA747A
Collector(+) + Pin 1 = .531
Collector + Pin 1(+) = .531
Collector(+) + Pin 2 = .428
Collector + Pin 2 (+) = 0.0
Pin 1(+) + Pin 2 = .480
Pin 1 + Pin 2(+) = .408
Is there a reason I am getting readings when the transistors are in circuit as opposed to out of circuit? Is this indicative of improper mounting?
I reused the mica sheets beneath the transistors and only used a small amount of compound.
In response to testing with headphones, the preamp is functional only on the left side (the side with the unmodified amp board). It also has quite a bad hum.
If you move the good module over to the right side (leaving the bad one out, you should get sound. That would prove the pre-amp ok, the hum is most likely because you have the bottom cover removed.