Batboard

I have a VHF CDM 1250 45 watt LDMOS with zero power output. My only clue is the collector of the driver transistor goes from + 12 volts to 0 volts when transmitting. Does this mean the power amp transistor is bad?

Not necessarily, it is a faulty component in the DC feed to the driver transistor.

Also check the power control circuit.

OK. Anyone have more advice? Depot is not an option.

Most of the time I ended up changing out the final. However if you have a good power meter or monitor with good probe this should help out. Keep in mind that your key ups should be short and if I'm not mistaken you'll have to have the cover "detector" pad on the radio in order to attempt to key up the radio. (This could just be with the low band but I'm speaking from long term memory here).

Step one can you adjust the power. I know crap power is crap power but if you can adjust it up or down that means stage one is good. (not likely bad in any case but not impossible either)

Step two check out the driver PA. This is pretty much the same part that is used in VHF portables just probe the output while keying up the radio. Keep in mind you will load the circuit down so you won't get really high wattage you are just looking for more than you get on your output.

Step 3 change the LDMOS final. Not really much checking here, you've already eliminated the other two circuits.

If I come up with anything else I will post. but that is what I have for now. Good luck

LDMOS is under $40 from Moto. You will NEED a hot air debonder....