I thought that maybe I could teach something today.
Here’s the trick, one does not really need to have every part number and pin-out memorized; as there are only 3 different voltages present. These are V+, V-(typically Gnd), and Out.
If there is any reason to suspect a power problem to a circuit the 3 legged regulator is a great place to start (provided it is not impossible to physically get to).
Connect the black lead of your “digital” meter (and yes to those that know, I was one of the two of us to keep an analog Simpson on my bench) to a quality ground point. Set the meter to DC and auto-ranging. Then, in any order that is easiest to do:
…Probe pin-1 at the left side of the devices connection to the pcb and note the reading on the meter.
…Probe pin-3 at the right side of the devices connection to the pcb and note the reading.
…Probe the tab on the top of the device and note the reading.
The readings should be stable, and make sense.
. 12V, 5V. and 0V make sense.
. 0V,12V, and a “floating near 0V” indicate a problem.
Note: The reason for not probing pin-2 is that it is way to easy for the lead of the meter to slip off of the round solder blob and short to either pin-1 or pin-3 and potentially damaging the device under test.
If anyone has any other hints to add, I’d like to read them.