Ian I have noted that a lot of toroids tend to be wound with low temperature spec wire.
That is the sort of wire that the insulation bubbles off if you stick a soldering iron on it.
Real wire needs a flame to burn the insulation off.
The low spec wire also has a poor mechanical strength and can develop a shorted turn simply by crossing over and those toroids have plenty of cross overs!
Unless you find a shorted rectifier I would go for the winding fault.
Keep up the good work.

Fred.

Hi Fred,

I have taken a few educated guesses in re-winding these coils ... some lessons learnt here ...

Wire and size - was given some reels of wire from old companies who used to wind transformers .... wood and metal reels with many metres of wire ... I am hoping that the older stuff is of a better quality than what I might buy today ie copper content, insulation etc.. I didn't have a thick enough single strand wire, so I doubled up on smaller gauge with larger total cross-sectional area. I taped between each layer to avoid shorting of windings. I am hoping that this doesn't lead to overheating when transformer is loaded.

Number of windings and voltage - luckily, I allowed for lengthening of each winding due to extra copper and tape ... and that proved correct. A couple of extra windings were needed to get the required voltage. I am guessing that the voltages I measured with my test circuit may 'sag' when the transformer is loaded.

I have tested all main components in the PSU Control Board and can find find no faults. This was mainly 'in circuit' testing as I don't want to risk damaging the PCB any more than maybe unavoidable ... there are some limitations to these results.

Interestingly ... comforting(?) .... worrying(?) ... each of the 4 supplies have IC's controlling the voltage with current sensing circuitry ... so it is a bit puzzling as to what would cause the cooked windings ... usually supplies like this just shut down. Time to re-assemble, add some fuses and Meters ... put on my Safety goggles ... .... and fire up the PSU as a stand-alone Unit.

Oh, I forgot to describe my Coil winding machine .... it keeps the wire held straight across the Lounge room floor and down the Hall to avoid tangling ... feeds the wire to me for inserting through the toroid hole .... lays the wire out on the floor again and waits for me to straighten out the wire around the toroid ... then repeats that process .... verbally controlled like Siri, sometimes. It also makes my a cup of coffee and Lunch ... running costs are very high ...... ...... any guesses?????

Lol, high-maintenance wife.

Hey Ian!
All of the above sounds good to me!
The wire you have probably is "motor" grade so the insulation will be polyvinyl high temperature grade.

Your insulation sounds good and your winding "shuttle" far better than mine!!
So modern, and voice controlled, WOW!
I have to stay in the workshop and do it all myself.
My VCS just looks at me and tells me to wipe my feet before I come into the house.

Fred.