Are you able to post a picture of the back of the rectifier board please?

this may not have anything to do with it, but...

did you trim back the wires, tinning them also before you soldered them to the rectifier board?

it's not a criticism here, just an observation, but some of the solder joins don't look to have taken well where the wire meets the rectifier board.

if only a few strands of a cable are making connection it isn't enough to carry the necessary current, creating resistance resulting in a voltage drop.

you could doing a resistance test for each wire from the transformer lug to the relative rec board header pins ?

i'm trying for a process of elimination

you mention connecting J2 only, as J2 has the mains voltage, can you remove the other pins, 1,2,5&10?
isolating the machine from the rec board.

or if you happen to have a variac make a plug with wires going to pins 6 & 7 on J2

so you only have the active and neutral going to pins 6 & 7 and see if there is any difference?

if i'm doing a rec board i use a variac to check the board prior to putting it back in the machine so i know it's ok, if something doesn't check out afterwards, i know it's not the rec board.

you confirmed the transformer outputs were okay, give or take a little:
E3 - E4 = 49VAC
E7 - E8 = 7.3VAC
E9 - E10 = 7.8VAC
E11 - E12 = 12VAC
E5 - E6 = 173VAC

what is your AC line voltage?

this is frustrating....

and the following may do nothing at all, but something is amiss causing the problem, and the fuses aren't going open so the bridges aren't shorted internally.
the transformer shows to putting out the correct voltages

okay, maybe try removing all the fuses, and putting in one at a time and checking the test points?