[ICOM] More on my Pro3 pwr issue

[kb4t at arrl.net]

I had a similar problem with my Pro3 several years ago. I found that the
power cabling that goes between the rear power connector to the power amp
module had developed an intermittent connection at the PA module. It's been
a while but my recollection is that the power connections to the PA module
are made using crimp terminal lugs and screws. I solved my problem by
removing (or loosening) the screws, removing the lugs from under the screws
and cleaning the lugs and the surface to which they connect. Once the
surfaces were cleaned and bright, I reattached the lugs under the screws and
tightened. Problem solved. 

I concluded that the mating surfaces had developed some sort of film or
something that introduced enough series resistance as current flowed to
create a significant voltage drop. Cleaning the mating surfaces eliminated
the series resistance under current flow and have not had a problem since. 

It was quite disconcerting to observe these symptoms. I confirmed that the
power supply was not dropping voltage at the rear power connector so I
pulled off the covers and traced the wiring to the PA module. It was at the
circuit board connections from the power supply that I found the voltage
dropping. With only a mechanical connection between the circuit board and
the wires, cleaning was the only solution. 

Essentially, one employs a "divide and conquer" troubleshooting process that
seeks to determine the root cause of the PA output power dropping. Likely
causes are RF drive dropping, operating voltage dropping or devices failing
during operation. Doing the simple and easy stuff first makes sense. These
steps are checking voltage to the active devices and inspecting for obvious
damage/opens in the voltage feed path. If the voltage remains at its proper
level when the transmitter is operated, you will need to look into the drive
level and device failure possibilities. Or send the radio off to a competent
tech. 

Hope this helps. 

73, 

 Frank KB4T
Florida