Brian, The PA transistors will normally take some abuse - for a short time, so put them in and do a short test to see what happens - just be aware of the conditions and keep the transmit times as short as possible while still allowing some measurements to be taken. Everything in life is a compromise, including this situation - TX time vs. potential abuse must be compromised to come to the resolution of the problem.
73, Don W3FPR On 1/9/2011 7:01 PM, Brian Handy wrote: > Don, > > You're absolutely right, I checked again across R98 just to confirm and you > are > on the money....5.6V at the drain. It seems possible this part may be working > fine. > > I understand the voltages are going to be different, the whole feedback loop > isn't there. I'm just hopeful to identify the problem before nuking another > set > of finals ... ! > > I'll keep looking. Thanks! > > Brian AE7JW > > > > > ----- Original Message ---- > From: Don Wilhelm<[email protected]> > To: Brian Handy<[email protected]> > Cc: [email protected] > Sent: Sun, January 9, 2011 11:27:58 PM > Subject: Re: [Elecraft] [K2] TX Issue in Part III checks > > Brian, > > Looking again at your Q24 measurements, I think you reversed the leads. > Check against the J310 basing diagram on the Schematic Key page and > remeasure. > > 5.6 volts on the drain is well within reason when there is no output - > VALC will go to its maximum value when there is no output sensed and > tries to make Q24 conduct harder so more BFO signal is delivered to the > Transmit Mixer. That is how the power control works - the conduction of > Q24 is the controlling element. > > The voltages listed in the DC voltage chart are for a properly working > K2 at 5 watts output. > > 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
