Well, I apparently mis-diagnosed my issue since after installing all the components in the K2PAKIT made little difference in the symptoms.
So, back to square one... Initial conditions: base K2 with KAT2 and KSB2 removed. 7.1 MHz CW, 5 watts set on power control. Transmit signal tracing: Basic voltage checks - pass Sidetone - pass ALC - pass up to item 4, VPWR around 4.5 VRMS Transmit mixer output - pass Buffer output - 1.38 VRMS Anode D7 - .46 VRMS D7 / R5 junction - .4 VRMS Junction C5 / C4 - .6 VRMS L1 / C6 junction - .6 VRMS C6 / L2 junction - 0 VRMS Thinking I had the issue identified, I replaced C6 with a 4.7 pF NP0 disc ceramic. Still no voltage at the C6/L2 junction. Removed C6 again, check pad/trace continuity to the top of L3, DC checked OK. Re-installed C6, no change. No output RF output on any band noted. I saw some questionable solder joints with T1 and T2 so I'm going to pull both transformers and rewind them. I have plenty of the correct magnet wire left over from previous K2 builds. I'm stumped at this point, so any guidance would be appreciated. Thanks and 73, John K2ZA Sent from my iPad On Aug 10, 2013, at 0:04, Don Wilhelm <[email protected]> wrote: > John, > > What is the DC voltage at the base of Q7/Q8 during a TUNE? If it is in > excess of 0.64 volts, then Q11 and Q13 as well as Q7 and Q8 are toast. Order > and install the K2PAKIT which includes all those parts. Q7 and Q8 are > connected in push-pull output, so a failure of one will reflect on the other. > > I don't know how that would change the behavior of the KIO2, so you may have > multiple problems in your K2. > > If you want to do a test, remove the KAT2 and try working into a 50 ohm dummy > load. If you then have good power output, the PA transistors are OK and the > problem lies with the KAT2, > > 73, > Don W3FPR > > On 8/9/2013 11:39 PM, John Zaruba Jr wrote: >> I was using my new to me K2/10 (S/N 50xx) which has been working flawlessly >> for the last 2 months when out of the blue I started getting a P LO message >> from the KAT2. I checked the power out with an external meter and it was >> about .4 watts in general agreement with the K2 power display. No snap, >> crackle, or other dramatics, just loss of power. Coincident with the output >> power failure, the KIO2 stopped working, neither receiving or sending data. >> Coincidence does not imply causality, so I'm going to treat this as a >> separate issue. >> >> I started signal tracing per the manual with a DSO scope (Tek TDS-210) and >> the RMS voltages I read on the scope were nothing like the voltage charts, >> so I was just looking at voltage gains from the various stages. I removed >> the KSB2 and installed the cap and 2 jumpers to eliminate that module, with >> no symptom change. >> >> The one anomaly I think I've found occurred with Q7 & Q8, the voltage at >> each device's base lead was 3.2 VRMS (as measured by the cyclic RMS setting >> on the scope), but the collector voltages were around 500 mVRMS. Just to >> clarify my thinking, I would expect the collector voltage to be >> significantly higher than the base voltage. >> >> As an additional question, if I have had a final amplifier failure, what >> might cause both devices to fail, rather than one or the other? Hopefully I >> can receive some wisdom from the list before I call the factory on Monday to >> order parts (to make sure I get the correct ones) I'm also thinking I should >> order new thermal pads and shoulder washers, if new finals are indeed >> required. > ______________________________________________________________ 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
