DCV on all terminals of the LM339?
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
I see 19v on pin 8 11 and 12 of the 494
Pin 1: 0.031
Pin 2: 4.67
Pin 3: 19.78
Pin 4: 0.273
Pin 5: 2.094
Pin 6: 4.94
Pin 7: 3.676
Pin 8: 4.014
Pin 9: 4.94
Pin 10: 4.94
Pin 11: 7.56
Pin 12: 0.001
Pin 13: 4.67
Pin 14:4.67
Pin 1: 0.031
Pin 2: 4.67
Pin 3: 19.78
Pin 4: 0.273
Pin 5: 2.094
Pin 6: 4.94
Pin 7: 3.676
Pin 8: 4.014
Pin 9: 4.94
Pin 10: 4.94
Pin 11: 7.56
Pin 12: 0.001
Pin 13: 4.67
Pin 14:4.67
Recheck. Either something changed while checking or the diagram (which is for an 801S but is the 4333) is wrong. 2 numbers don't seem right.
It still seems a bit strange but let's check something else. Do you have audio reaching C201 and C304?