I finished assembly and started the calibration and checkout. All my preliminary resistance checks were nominal. When I put the unit in tune mode, the power indicated 3/10 watt and remained there while I tried to adjust L1. After a few seconds I saw a faint puff of smoke and HI CUR appeared on the display so I immediately shut the unit off. I touched the driver transistor, Q6 (2SC2166), and it was extremely hot. I remeasured the resistances on Q6 and found that Q6 base to ground, which had read 118 ohms now reads 68 ohms. R50 (emitter to ground)which should have read 1.5 ohms now reads 1.8 ohms.
I removed the bottom covers and saw where the smoke came from.....R50 was burned but not open circuit. Resistance checks on Q6 (emitter to base, collector to base and emitter to collector) look nominal as far as I can determine in circuit. I rechecked T1 and T2 construction and installation visually and with an ohmmeter and all looks okay. Resistance checks on Q7 and Q8 are still okay. (As far as I could determine at the time of the problem they did not overheat, at least not enough to warm the bottom heatsink/cover.) Any ideas where to start looking? My thoughts are to check for RF waveform at Q5 collector and Q6 base with a quick push of TEST and then release. Am I heading down the right road? I'll wait until I hear before proceeding. I'll also order a new R50 but will wait to see if something else has fried. Thanks, Pat Haynes-K4BEH _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
