[Kenwood] TS940 PS problem

Tue Jun 20 01:20:55 EDT 2006

I just finished (well, almost!) repairing a TS940S which suffered a shorted bridge rectifier in the 28V power supply. Well, the radio now powers up and works, but the transmit power fluctuates all over from 25-100w. Also, the IC current meter and ALC meters are not working. The LM-324 style U9 op amp on the control board, which derives the metering circuit, seems to be fine, as well as the associated components. I found that the circuit monitors the voltage drop across a high-wattage resistor in the 28v rail feeding the final stage, and the points across the resistor are fed to the op amps thru .15mH chokes. 
The voltage at this point, while only a 150-200mV, seems to vary up and down, and proportionately to the RF power fluctuations. The resistor itself seems to be ok, so I am thinking that maybe the chokes are starting to act up. They check good when out of circuit, but I seem to recall finding a similar problem a while back on another rig, and it was caused by chokes that were not funtioning properly yet measured good DC-wise.
Anyone have a similar situation with a TS930 or 940?
Eric
KE2D