X68000 ACE HD Memory Expansion

[lydux]

2SK643 found new on eBay

Ok fine ! Just to let you know : there are cheaper and better alternatives nowadays.

I noted that the DC voltage from the rectifier was measured in excess of 140v. Maybe because the step down transformer was on the way out?...

Maybe... Highly possible.

Would this cause the noise from the transformer?

Highly possible as well ! I hope nothing else passed out... Especially this main transformer ! Because it'll be hard to find a replacement.

I've ordered a new 300w step down transformer with fuse protection 

Excellent choice ! 

[X-Col]

New step down transformer arrived.
Blew the fuse as soon as plugged into the PSU. 

Found Q1 mosfet was touching the case. Worked after that but high pitched squeal still heard from transformer. Unit powered on as normal and correct voltages output.
Noise from transformer stopped suddenly and no power to X68000, no red standby.

Update: replaced the fuse in the PSU and working again. Although the high pitched 'squealing' sound still comes from the transformer. Here is a video of the PSU as it is now, turn up the volume to hear the noise I mentioned as the video is pretty quiet. https://www.youtube.com/watch?v=BlUyz4L9qyo&list=UUpdEEkadgCceijY-RKZEv1A

If it's just coil noise due to it being an old transformer (and it's not dangerous), I'll just live with it for a while (I'll replace it with an ATX PSU eventually). At least you guys helped me get it running, much appreciated!