I have a number of SMPS boards that should give me 12V and 24V on the output side but only give 12 and 1.2. I can't figure out what in hell is wrong with them.
I don't think there is anything wrong with your SMPS. At the bottom-centre of the top-side of the PCB (second photo), there is a connector labelled 'CONTROL'. I think the connector requires feedback to enable the normal operation of the SMPS. 4 of the pins go to optocouplers (output side, i.e transistor/switch) and 3 of the pins go to zener diode circuits.
Can you test the zener diodes? Which pin is anode and cathode? It looks like the top pin is the cathode.
I think the reason that the +12V rail is working is because it doesn't require a trigger or switch to enable it.
You could try using a pull-up (or pull-down) resistor (10k ohms) between the 3 connector pins and GND (or +12V). The resistor is for current limiting purposes.
I noticed that some of the fuses are missing or are they not required?
Without a full schematic it's very difficult to know what to do.