Query on relacing RF mosfet 2SK3476 on a radio transmitter pa component

[bcoleman1]

Hi All,
Hope all is well.
Query on relacing RF mosfet 2SK3476 on a radio transmitter pa component. Should the radio transmitter in question working for rx/tx i.e send and receive signals, get on network, if rf mosfet is replaced and soldered back on correctly?

I tried so solder back on new rf mosfet, however some units still flash amber on acknowledge LED light on transmitter and wo't connect to the radio mesh network while one or 2 others I worked on are completely dead. Presumed may need desolder and clean, resolder again.

radio units in question are within the last 10-14 years old and is relatively good condition otherwise. I have seen a common issue with several of the radio units output stage blown on pa component. We discovered that the rubber duck like 18 inch antennae is causing this issue mostly. We have adopted a better antennae solution in the meantime.

Appreciate any feedback please as I am under pressure to get a number of these units back in working order. Used as fire/intruder alarm units in radio mesh network setup btw.

Thank you.

 

[prcguy]

I would suggest running tests to determine what is wrong the the transmitter or radio before changing any parts. A wattmeter and 50 ohm load will tell you if the transmitter is making rated power. If its not then the PA transistor is suspected but not always the case. Further testing is required with RF millivolt meter, RF probe, spectrum analyzer with appropriate probe, etc, to determine if the PA transistor is actually bad or if some other component or connection is the problem.

If the radio/transmitter is in the VHF/UHF or higher bands component spacing, lead lengths and other things become very critical, usually requiring a realignment of the transmitter after a component change. Working on RF equipment is not like changing a band light bulb, there are lots of things to consider.

Working on RF equipment without the proper test equipment might be compared to working on a motorcycle engine and your tools are a cheese knife and spoon. Fine for a Chef but not a motorcycle tech.

 

[bcoleman1]

I would suggest running tests to determine what is wrong the the transmitter or radio before changing any parts. A wattmeter and 50 ohm load will tell you if the transmitter is making rated power. If its not then the PA transistor is suspected but not always the case. Further testing is required with RF millivolt meter, RF probe, spectrum analyzer with appropriate probe, etc, to determine if the PA transistor is actually bad or if some other component or connection is the problem.

If the radio/transmitter is in the VHF/UHF or higher bands component spacing, lead lengths and other things become very critical, usually requiring a realignment of the transmitter after a component change. Working on RF equipment is not like changing a band light bulb, there are lots of things to consider.

Working on RF equipment without the proper test equipment might be compared to working on a motorcycle engine and your tools are a cheese knife and spoon. Fine for a Chef but not a motorcycle tech.

thanks for the informative and constructive feedback, appreciated. Rgds, Barry