Failed voltage check. [tentatively resolved]

No, A3 and A8 wouldn't be 174V.  That is pin 3 and pin 8 on the 9 pin socket.  No pins on the 9 pin socket should read that high (although 1 and 6 will for about ten seconds when you first turn the amp on).
 
Yes, 3 is a ground.  It looks like your amp is working properly now.  I would poke around with a wooden chopstick and a cheap pair of headphones plugged into the amp to be sure nothing causes a popping noise when you poke around in there.  If you have a loose connection and you poke it, you will get a pop through your headphones and that can help refocus your efforts.
 
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