Analysing the rest of the board
It’s great that I can use the board as a 3.3V power supply as-is, but it would be really nice if I knew what the little golden fingers on the edge connector did. To help with this I photographed and printed out both sides of the PCB.
Having it down on a piece of paper really helps because you can jot down notes directly onto the image as you discover things. On the PCB side I labelled the little fingers A through F. Here’s what I managed to find out about them.
| A | B | C | D | E | F |
|---|---|---|---|---|---|
| 3.3V | NC | 12V | PGOOD | 12V | NC |
The 3.3V and 12V outputs are a mystery to me. They snake off through many components in the direction of the op-amp and the values don’t seem to change with load.
PGOOD is an easy one. That’s an open-drain output from the Intersil IC that floats when everything’s fine and is driven to ground when it’s not. Apply a pullup resistor to your MCU’s IO supply to sense the output of this pin.
I did the same sort of thing on the heatsink side, labelling the pins G through K. Here’s what I could find out.
| G | H | I | J | K |
|---|---|---|---|---|
| NC | NC | input | NC | input |
Only two of the contacts are actually connected to anything. I probed them and found that they weren’t driven to any particular level so I measured the resistance to ground and found it to be more or less exactly 50Ω which would appear to make them input pins.
I guessed that perhaps these pins formed part of an external resistor-divider that might calibrate the output voltage so I tried applying various resistances to ground, to the output voltage and using a potentiometer to create a divider. The good news was that there was some response from the output voltage as I experimented, but only ever upwards. That is, all I could do was cause the output voltage to rise slightly, nothing I did caused it to fall which wasn’t much use.
