Trace Elliot 1215 Hum on output

[ElectricEel]

Hi, I'm a freelance service engineer, I have an amp that has stumped me!
It's a Trace Elliot 1215 12ch EQ Amp

The Fault is a mains hum on the output. with all gains down and nothing on the inputs I get a noticeable hum on the output.
I've replaced the caps and rectifiers in the power supply but this hasnt fixed it. If I remove the mains transformer from the case and turn it on the hum disappears.

Can anyone help with this or has anyone had similar problems and managed to get it resolved?

Darren

[52 Bill]

If I remove the mains transformer from the case and turn it on the hum disappears.

If you electrically ground the transformer core/mounting lug when it is removed from the case does the hum return?

If you place the transformer in the case and rotate it can you make the hum lessen or stop?

[ElectricEel]

If you electrically ground the transformer core/mounting lug when it is removed from the case does the hum return?

If you place the transformer in the case and rotate it can you make the hum lessen or stop?

Thanks for replying,

If I ground the tx, it makes no difference. But if I rotate or move the tx around the chassis it comes and goes, but never disappears completely until I move it out of the chassis.