Page 1 of 1
VHF 45W CM300 - Low Power Issues
Posted: Fri Nov 05, 2010 1:00 pm
by ummhello1
We have received several VHF 45W CM300's in the past few weeks with low TX power. They will range anywhere from 12W to 18W even on "High" power. Has anyone else experienced this issue?
Jeff
Re: VHF 45W CM300 - Low Power Issues
Posted: Sun Nov 07, 2010 3:56 am
by Al
More than likely a defective transmitter PA. Those PA transistors are LDMOS, and they fail partially because some of the individual transistors in the package fail. If the DC current drawn on tx is low, and you're unable to make rated power output even with the soft controls set at maximum, check the forward bias on the PA. If it's low, check for gate-source low resistance/shorts. If it's low, that should be the cincher.
And good luck finding a Motorola p/n for the thermal pad that sits between the transistor case and the chassis...I haven't been able to get replacements from M. They tell me that there's no p/n. If you find a suitable replacement, please post what you found.