[Coco] CoCo 3 Power Supply Question

[Mike Rowen]

Hello all. I have a little reclamation project going on. At last year's
CoCoFest, I purchased an old AT chassis that was used for some sort of
kiosk application that contained a logic board and an entire CoCo3
motherboard. I have removed the CoCo3 board and it seems to be unmodified
except for one component and this is what my question is about.

There is a 100 ohm resistor soldered between the cathode of D2 of the
bridge rectifier and the cathode of D13. Power was connected from the PC
switching power supply at the normal transformer connector, but the input
power was -12VDC and +12VDC, rather than 12VAC from a transformer. I have
not encountered this method of powering the CoCo before.

Can someone with circuit analysis skills tell me if this would work, why
the 100 ohm resistor would be necessary, and whether this configuration
could damage or shorten the life of the power supply components? Your help
is appreciated! Thanks!

Regards,
-Mike Rowen