My LM350 regulator with smoothing caps (C1:0.33uF, C2:1uF polarized, R1:150 R2:10ohms+trimpot) does not work. It works without capacitors. I am an idiot. What have I done wrong? I tested all the connections, and they match up fine with the diagram. On Vout, there is briefly a nice voltage, then it drops. When I retest with my DMM a few moments later, the voltage is up again, then it drops.
What is wrong? Hit my stupid skull with your cluebats!
Edit: Had the same problem with a LM317 voltage regulator. I 'fixed' it by removing the caps. But I really want to know what I'm doing wrong here. The LM350 is confirmed working – without those caps.
Edit2: This question has been answered by @sstobbe. I had a bad solderjoint in an inconspicuous location. Thanks for your time everyone.
Best Answer
Resistors R1 & R2 are constantly loading the output. So, having the output voltage sage due to probing the output with a DMM is suspicious.
Its likely a bad solder joint somewhere. When you apply pressure with the DMM probes, you break a connection.
It could also be that the output is oscillating and the impedance of you holding the probes plus meter is sufficient to detune whatever is oscillating.