TS-930S power supply

September 28th, 2008 by k8gu Leave a reply »
Benched TS-930S

Benched TS-930S

Remember how I said that I thought the W9RE switchbox had terrible isolation?  Well, although I didn’t measure it with a VNA, I was doing some testing the other day and noticed that it only seemed only bad when the left radio was transmitting.  For example, I put the left radio on 40 meters and the right radio on 20 meters.  There was terrible broadband hash whenever I closed the PTT line on the left radio.  So, I put the right radio on 40 and the left radio on 20 and transmitted again on 40.  No hash, just some faint trash that followed the keying.

I had noticed during the Sprint that the vacuum fluorescent display on the left radio was flickering following the keying.  But, I didn’t give it much thought until now.  I flicked the meter selection switch to Vc and sure enough, it was too high (>28 volts) on transmit.  Plus, it would spike and pin the meter whenever I released the key.

Today, I built a band decoder cable (fortunately, I had stocked-up on the mini-DIN plugs and the PIEXX board uses Yaesu BCD format) for the Yaesu FT-840 and put it into the left radio position. It’s clean, too.
The left ‘930 is now on my workbench, which is barely large enough for it.  It turns out that there is a substantial (4 volts peak-to-peak) ripple on the power supply when I close the PTT.  I sent a note to the TS-930S reflector; but, unless KA5IPF answers it, I’m probably on my own.  I suspect it’s just going to be a matter of disconnecting subsystems until I find the offender.

Until then, I’ll be using the FT-840 and the old TS-930 for SO2R.  But, at least I’ll be able to hear!  I’m also relieved that I probably won’t need to rewire W9RE’s switchbox.  I just need to build some short jumpers and W3NQN filters for all bands.