Brian, The DC voltages on Q24 are based on a properly working K2 at the 5 watt power level. What you now have is a K2 that will not develop power to the RF Detector, so the power control circuits will react to force the RF voltages to their maximum - the control element for that is the VALC voltage to Q24, and that will go to its maximum since there is zero power detected.
I note that you measure zero volts at the drain of Q24, but VALC at the source (CB emitter of Q8) is at 7.4 volts. Something is broken (not soldered) between those two points because the only component between the two is R98 which should not be drawing any current and therefore should not have any voltage drop (given your situation with no power output). Look for unsoldered connections (don't forget the connectors) or solder bridges in that signal path. Look critically at you soldering - if the solder did not flow out to an almost invisible edge on the solder pad, it is suspect, and the likely cause is that the solder pad did not receive enough heat. Re-flow the solder on all suspect connections using a hot (750 deg F) iron, and add a bit of flux if necessary. 73, Don W3FPR On 1/8/2011 10:44 PM, Brian Handy wrote: > Hi All, > > I've been working on my K2 and I'm on the home stretch. I had to dabble a bit > to find a cold solder joint in the Part II checks, but eventually got a > home-brewed test oscillator to reach through on 40m! Quite happy with things > so > far, and learning a lot. > > I still have a lot to learn about the transmitter side though, that doesn't > work. When I first hit 'tune' in the Part III checks, I noticed high current > on > the power supply, high current on the front panel, and changing the power > level > didn't help, it was always high draw. > > It didn't take much of this to zorch the PA finals and short things straight > to > ground. Nothing worked until I pulled T3, and while I had the soldering out I > took out the PAs and started looking around and reading the mail archives. > > I noted one suggestion from Don to someone else and checked the voltages on > base > on the finals - both are around 0.65V, which I think is OK. > > I realize things won't be quite the same without the PAs there and proper > feedback happening, but ... I then started going through all the voltages on > the > RF board with TUNE on. Everything looked pretty much fine except for Q24 ~ > > Leg - Expected - Measured: > G - 0V - 5.6V > S - 1.2 - 2.5V > D - 13V - 0V > > That doesn't look right at all to me. Exploring further, I started chasing > VALC > down the rabbit hole. > > Pin 2 of U8 (V PWR) seems to vary between 3.8-5V as I turn the PWR knob in > TUNE. I decided that was OK. > > Pin 1 of U10A doesn't move around a lot, only up and down about 0.1V. Finally > the emitter of Q8 (V ALC) seems stuck at 7.4V. > > I was firmly confused at this point, so went back and started checking Control > Board voltages per the page of expected readings in the back of the manual > with > CAL FCTR turned on. Everything seems turned off when I do that and I'm seeing > pretty much 0V everywhere. > > I'm a bit saturated at the moment, but thought I would ask if this sounds like > I'm on the right track, or if I have to get to poking elsewhere ... > > > > Cheers and thanks in advance, > > Brian Handy > AE7JW > Tokyo, Japan > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
