Vintage Synth Repair

Hi everyone .

I am working on a Jupiter 6 PSU and I am having problems with the 5v dc.
It seems that when the psu is disconnected from the synth then everything is fine and all readings are correct.
However, when I connect the PSU to the synth I lose the 5 volts, they drop to about 0.7v.
+-15v stays intact and I get the somewhat classic blinking light on the LFO 2 board.

It seems that whatever card I plug in I lose the 5v so it seems like a PSU problem rather then something downline.

Any ideas to help me get this synth up and running?

Thanks 
Arnar