On Thu, 21 Jan 2016 22:06:02 +0000, Cydrome Leader wrote:

You're running a switcher at way out of spec input voltage. The
magnetics making awful noisy or hissing sounds is not unexpected under
those conditions as it fails to startup correctly.

Well I've now wound it up to the correct supply volts and it's still
hissing. Nothing's blown that I can see; there's just one power resistor
that's running too hot to touch (because the psu is unloaded?)everything
else, including the transformer is cool. Also, by use of better gauge
pipe, I've been able to detect the sound is coming from the grey 1.5kV
transformer in the middle of the board:

https://www.flickr.com/photos/128859...2/16727519128/

Could this be just normal behaviour that we don't normally hear since
it's normally buried deep within the scope casing??

BTW, those burnt areas are previous problems that someone else fixed
years ago and not relevant to the current issue.