Diodes are usually marked 1N4007 or something like that.
You could check here:
I'd go for at least 2A ones, maybe the 1n5408 - if the pins will fit the original holes.
One of the 9VAC pins in the connector looks very bent, does it go in correctly?
The iron core transformer itself can make a buzzing sound, only way around that is to put put a bunch of epoxy on it, wait for it to harden and then check again and add more if it's not quiet...
You should measure close to 5V DC on the closest together pins in the DIN-connector. Multimeter set to DC, then probably 10VAC on the other two pins with the multimeter set to AC.
If that's OK I'd measure the 5V when turning computer on, if it stays at 4.8-5.2 everything is cool. Goes over 5.5V shut it down right away!
The user port is an easy place to measure, or over a logic IC if the computer is open. The large capacitors on the right is an easy place as well to attach a clamp. GND for measuring 5V is everywhere...
If it's on and you start hearing the buzzing noise, try pushing the iron core transformer with an isolated material, to check if the sound changes. Not uncommon that the caps can make noise as well... next thing to press.