[michaelsmith1160]

Test point v48 yields only about v14. All other test points are fine. What even more weird is that a budge 500 series pre amp works fine and doesn't seem to be starved for power. It's a solid state pre, no transformers or tubes. Is +48v required for normal operation or is this necessary only for extremely power hungry 500 series modules? Thank you!

[JPK]

The 48V is only in use when using a condenser microphone which needs phantom power.
Does the 55V come out of the the switcher? It can be measured on R7 on the 501 PCB.
If not, the 48V is built from T1, D1, R6, C6, C9 C14, L1 in the switcher. Check the value, direction and solder joints of these components.