Larry, With those RF voltage measurements, I would say that the final output transistors have likely failed - that goes along with your earlier report that the power out decreased rapidly to zip.
There is only one other possibility that I can think of, and that would be the transmit signal being shorted somewhere - so before blaming the finals themselves, check that Q2 is operating properly - the juction of D3 and D4 in the TR switch should be at a low voltage during receive and go up somewhere close to 8 volts during transmit. If the receiver is still functioning properly, a short in the Low Pass Filter is quite unlikly because that kind of fault would drag the receiver way down too. 73, Don W3FPR > -----Original Message----- > From: Larry Phipps [mailto:[EMAIL PROTECTED] > Sent: Sunday, December 11, 2005 10:46 PM > To: [EMAIL PROTECTED] > Cc: Elecraft@mailman.qth.net > Subject: Re: [Elecraft] K2 dead xmtr > > > > Hi Don. The levels are high everywhere in the chain up through the bases > of Q7-8. Requested power is immaterial in this case, since the ALC sees > zero detected power, and therefore is pegged at 5v all the time. > > I measured the levels with a scope, and divided the p-p values by 2.82 > to compare with the voltage probe reference levels in the manual. BTW, I > removed the KAT2 and KSB2 to simplify access and minimize the number of > possible fault zones. > > W6 - .28 Vrms > Q5 case- 1.4 Vrms > Q6 tab- 3.5 Vrms > Q7,8 base- 1.4 Vrms > RF out- .55 Vrms > > Note: These waveforms are pretty dirty looking except on 10m, where I > made these measurements. > > Larry N8LP > > > > Don Wilhelm wrote: > > >Larry, > > > >With the requested power set at 5 watts, send us the RF Voltage levels at > >the W6 jumper, Q5 collector (case), Q6 collector (tab), Q7,Q8 > base, and the > >RF Output jack. With that info, we should be able to home in on > the problem > >area. > > > >73, > >Don W3FPR > > > > > > > >>-----Original Message----- > >> > >>OK. I'm hoping someone has seen this before I start tearing into things > >>(and tearing my hair out). > >> > >>My K2 started to lose power yesterday. Within an hour, the output > >>dropped to close to zero (1mW on 160m, 40mW on 10m). There are no signs > >>of distress or burning odors. > >> > >>I checked the ALC... pinned at 5v. Everything looks good in terms of > >>levels/frequencies thru the XMIT mixer and filters, except the rf levels > >>are higher than indicated in the manual. I suspect this is due to the > >>ALC being wide open. > >> > >>The dc levels for Q5, Q6, and Q7-8 bases are normal, and the resistance > >>checks on Q7-8 are OK. 8T looks fine. But the rf levels are all > >>considerably high, and look pretty ratty except on 10m. The rig draws > >>about 600ma in xmit. > >> > >>Anyone seen this before? > >> > >>Larry N8LP > >> > >> > >> > > > > > > > > > > > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.1.371 / Virus Database: 267.13.13/198 - Release Date: > 12/12/2005 > > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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
