After looking at this thread again, I realized that some people might have a problem with the DC voltage tests. I made my first crystal set when I was 8, and 70 years later I'm still experimenting with electronics, so I've had a chance to do plenty of testing.
It's easy enough to test the DC voltage of the power supply without the preamp connected:
1. After unplugging the AC, insert a short length of no.18 gauge solid wire (same size as the center conductor of RG6) into the center of the "From Antenna" coax jack on the 0747 Power Supply.
2. Use a clip lead to connect the positive probe of the meter to that wire.
3. Insert the AC plug, and touch the negative meter probe to the outer threads of the power supply coax jack to read the voltage.
It's a little more difficult to measure the DC voltage of the power supply when the preamp is connected, because you don't have access to the center conductor anymore. You could open the power supply to measure the voltage, but that is a lot of trouble, and it isn't easy to get the AC wires back in place to replace the cover. To my knowledge, there isn't a T adapter for F connectors like there is for BNC, so you need to improvise:
1. After unplugging the AC, insert a short length of no.18 solid wire into the center of the "From Antenna" coax jack on the 0747 Power Supply.
2. Insert the other end of that wire into the center of an F-81 coupler that has been put on the end of the coax to the preamp that normally connects to the power supply.
3. Use a clip lead to connect the outer threads of the connector on the power suppy and the F-81 coupler, to connect the grounds (shields).
4. Connect the negative lead of the voltmeter to that gound connection, plug in the AC, and touch the positive probe to the center conductor to read the voltage.
If the voltage for the first test was about 22 volts, and the voltage for the second test is about 18 volts, that's normal. (The preamp could be defective in other ways, but that is rare.)
If the voltage for the first test was about 22 volts, and the voltage for the second test is near zero, then you probably have a short in the coax to the preamp.
If the voltage for the first test was about 22 volts, and the voltage for the second test is also 22 volts, then you probably have an open in the coax to the preamp.
If the tests are inconclusive, then you need to make some ohmmeter tests (no voltage on the coax please; disconnect both ends of the coax before making ohmmeter/resistance tests) of the coax that goes to the preamp to check for opens and shorts as I described in the other thread, post #18
If you still can't figure it out, then it's time to substitute another preamp.MikeBiker
Please let us know how it came out.