Vintage Synth Repair

>>How about before you blame the PS you make sure that there isn't
something of an excessive load pulling it down?  Could be that,  or
the PS,  and you're assuming there without anything I'm seeing posted
to indicate one way or the other...<<

I know it's a different kettle of fish altogether, but I recently had
a fault on a studer b67 deck where the -12V was apparently being
pulled down to about -9V by some rogue component on one of the audio
cards; the symptoms went away with all the audio cards pulled, leading
me to exonerate the power supply & spend a small fortune on tantalum
capacitors. 
I anticipated replacing capacitors on all of the boards, & began by
putting them back in one at a time to begin fault-finding. but on a
hunch, I tried a dummy load on the power supply first (actually just a
small light bulb like the one in the deck's meters) & discovered that
the regulator was fine off load but couldn't deliver anything more
than 20mA. changed it... deck now fine, but I'm down about £50 on
tantalums I don't need. :-(

the offending component was an LM320, a series regulator that looks
like a power transistor. the way series regulators fail never ceases
to surprise me- I had a 7812 in a pro-1 fail into short circuit, so
that it passed about 19V to the board & fried the vcf chip.

hth-
duncan.