Vintage Synth Repair

Thank you all so much for tips so far.  

I took some measurements of the ICs in the power supply, the rest of the device was connected during the measurements.  I used the center leg of the 7805 as the ground reference.  I'm making up board numbers here, so if a schematic exists and happens to turn up (please please please), don't take these numbers as reference... IC 1 may not be IC 1 on the schematic, I'm just numbering them right to left.

IC 1:  7805  
in  10.6v   
g   0v
out 4.86v

IC 2:  7806
in  16v
g   0v
out 5.98v

IC 3:  8535  (7906)
in  -15.9v
g   0v
out -6v

the last part was a little hard to find..  8535 apparently refers to an AVR microcontroller now, but I found this cross reference:

http://www.datasheetarchive.com/5962-01-068-8535-datasheet.html

which lead me to this:

http://www.datasheetarchive.com/KA79M12-datasheet.html

It also says 7906c on it, which was much easier to find:
http://www.alldatasheet.com/datasheet-pdf/pdf/91828/MOTOROLA/MC7906CD2T.html

The input and output of IC 1 seem out of line... should I also measure this with the rest of the device disconnected to see if it changes?  

What next?  Replace IC 1?  Test the diodes?  Measure resistance of each diode in both directions with the power off and look for one that conducts in both directions?  

Thanks for your help, any pointers would be appreciated!

Christian