repair notes
28.5-volt Power Supply

This is perhaps an obvious extension of what is in the W6NL document. However, it pertains to my repair, which may make it of interest to some. I'm confident that my failure was limited only to the 28.5-volt high-current supply because I installed W6NL's mods soon after purchasing the radio.

One day, I was testing a new antenna and the internal SWR meter on my TS-930S ceased to indicate. I tried the power meter setting and the Vc. No power out and the Vc was pegged. I slid the top cover off and read about 40 volts on the 28C terminal of the power supply. The other voltages in the service manual schematic read fine. Thus, I suspected the 2N5885 regulator pass transistors on the heatsink behind the power supply.

The 2N5885 is a relatively inexpensive transistor, about $3 each in small quantities. It can be obtained from a number of suppliers, although I purchased mine from Mouser Electronics.

After replacing the pass transistors, be sure to reset the voltage to 28.5 volts for proper operation of the PA using the trim pot accessible with the top cover removed. Alternatively, you may consider reducing the voltage slightly to reduce the risk of wear on the drivers. I have not tried this and take no responsibility for doing it as you may damage the radio due to an increase in current. Lowering the voltage may adversely impact the biasing of the PA as well.