Discussion in 'Radio Circuits, Repair & Performance' started by W1GCI, Sep 11, 2019.
These are soldered.
Yes, as has been mentioned the Driver Transistors in the '930 and '940 are very near their maximum DC voltage limit . . . so the slightest spike from the PSU and they will fail. (unlike the PA Transistors, which never seem to)
Having read various articles, it seems that the PSU spike problem is caused by the fact that Kenwood disconnect the PSU Output from the rig every time you turn it on and off ! So I provide a permanent load on the PSU which will hopefully stop this happening - that load is a pair of 24V Fans connected directly to the Regulator Output - these have replaced the original Fans on the Regulator and PA Heat Sinks. (and running all the time also stops them getting hot in the first place).
And yes, when one of my Drivers went EB open circuit (prior to doing this PSU mod), I replaced them with a pair of 2SC1969 transistors (which have similar gain), fed by a 3 Amp 7812 regulator IC. No other mods are required, and the rig (and another one I modified) have been working fine for about 3 years.