I've built this circuit: http://www.tuxgraphics.org/common/images2/article379/powersupply.gif
Here is a closeup of the amplifier section which I've built:
And in the instructions here http://www.tuxgraphics.org/electronics/200506/article379.shtml Guido suggests a testing routine:
Test1: Connect some powersupply (at least 15V) to the power input of the circuit and check that you get 5V DC behind the voltage regulator.
Test2: Measure the output voltage. It should be 0V.
Test3: Connect pin 7 and pin 26 on the microcontroller with a wire (no microcontroller in the socket). You should get on the output a couple of volts less than what is used at DC input. Remove the wire and the output should go back to zero. Be sure to not cause any short circuit on the output.
I'm stuck on Test3. I get 0 volts output when I connect pin 7 (Vcc) to pin 26 (end of DAC output). I've quadruple checked all transistors and matched their pinouts and orientations. I've tried replacing a couple of them incase thats the problem. However, now I'm trying to understand a little theory to understand how to debug it with a multimeter. What voltage drops could I measure to find where the problem is? I can probably gain access to an oscilloscope of that would help, however I am dealing with fixed DC voltages so I would think a multimeter would be enough.