[Kenwood] TS711A T/R switch problem

Sat May 15 22:24:42 EDT 2004

Hi Everyone,
I have a Kenwood TS711A, which is a fine radio except for one annoying problem.
When I try to run schedules, I burn up the PCB surrounding the T/R 
switching diode due to the duty cycle of transmit vs receive. I've had this 
thing repaired by Kenwood several times, each time they patch the pcb and 
put in a new switching diode and tell me not to use it key down for such 
extended periods.
This problem happens whether I run it at 2 watts or whether I run it at 25 
watts output. At 2 watts, the heatsink on the back barely gets above room 
temp, but the receive eventually fails due to heating of the pcb 
connections to the t/r switching diode. The solder actually melts and the 
receive path opens.
Each time Kenwood fixes it, they say they replaced the diode even though it 
tests good electrically.
I DO NOT believe this problem is related to the actual amount of output 
from the transmitter as it fails whether I run 2 watts or 25 watts.
I should note that the front end transistor has never blown and the 
transmitter has never failed either.
Has anyone else observed this problem or know of a fix?
Thanks,
Art