Thanks everyone for your replies! Just to reiterate, I'm really curious about those who are powering their SG503 through the TM5000 not TM500. The reason being is that they have very different supply voltages. For the TM5000 and TM500 they supply -26V vs -33.5V and 8.2V vs 11.5V, respectively. So I've come to the conclusion that the -20V and 4.7V that I am measuring is normal when powering it with a TM5000. Especially now that I have shown it works fine. I'll look into it further if someone can prove me wrong!
@Adam
Regarding R624, I made so many measurements on the power supply circuit I forget at this point! But both the 5.2V and -22V rails are clean and smooth signals. Very little ripple. Sounds like you have your work cut out for you with your SG503!
@Eric
Thanks for the tip! I definitely don't have that cable. I'll have to look into that.
@Siggi
I have adjusted the -22V trim pot as low as it could go which is -20V. But again, this is powering the plug-in with a TM5003. After all the troubleshooting I've done, I'd be willing to bet the rails would be normal if I was using a TM500, but I don't have one. Especially when you consider the LM723. It needs a differential of 3V. And the TM5000 series has an acceptable range for the -26V rail anywhere between -23 to -27V. Mine currently outputs -25V.
-Frank
Frank Mashockie