Hi all,
I've had an FT-301 for a couple of years, waiting for restoration. Finally got it on the bench and have been working thru the issues. I thought I'd share information about the biggest issue, which I've just solved. The radio was receiving pretty well, but not putting out as much as a milliwatt. I discovered that the PA brick is fine, and couldn't see any issues with the 10 watt amp either.?After some probing with a voltmeter I realized that there was no Switched Tx 13.8v. So started tracing that circuit, and soon enough found that L2, a 35 uH choke connected to one of the feed-thru capacitors on the underside of the rig, was open.
I replaced L2 with a similar value inductor (with a diode "backwards" across it), and immediately on keying up I was startled by a small explosion and smoke!! A tiny black component going from the downstream side of the choke to ground had fried. Whatever it was, it wasn't in the schematic as far as I could tell. But then I noticed an identical part on the other side of the choke, again going to ground. This one was labeled as "6.8 20v", so a capacitor. Not a form factor I'd ever seen before, but perhaps an early version of a tantalum? (small, black, rectangular shape)? Old tantalums are known for "exciting" fireworks on occasion.
Anyway, I replaced both with 6.8 uF electrolytics even though, as I mentioned earlier, I could not find them in the schematic. Clearly they, along with the 35 uH choke, are designed to keep RF out of the Switched 13.8v Tx line. After that I powered up the radio again, and it now puts out a solid 90-110 watts, depending on band.
I've already replaced all electrolytics in the radio, tightened every screw, have cleaned the card-edge connectors and of course also the case and knobs got a good scrub. Before doing a full alignment my next chore is to do something with the dial and S meter lamps. I find them woefully ... BLAH !! I'm not sure how else to describe it, but they just do not do the radio any justice. I'm going to put in LED's, and may mess around a bit to find some sort of (slight) color filter to give them a bit more "pizzazz." Any suggestions?
Joel, VE6EI
Joel Weder, VE6EI