Mark, I don't think the finals are the problem. I would check Q3 for good soldering and the value and soldering of R5 - make certain you used the 1k trimmer at R6 rather than the 100k trimmers for R26 and R27. The soldering at U1 pin 5 should also be checked, and be certain U1 pin 5 is not bent under the socket or sticking out the side. Make certain there is 5 volts on one end of R5 - if not, find out why.
The temperature of the heatsink is sensed by the conduction through Q3 from the base to the emitter (and collector), that resulting voltage is sent to U1 pin 5 for calculation by the firmware - it has nothing to do with the actual PA transistors, just the temperature of the heatsink at the Q3 location. 73, Don W3FPR On 11/26/2011 1:04 PM, Mark Flavin wrote: > Yeah. I did that too. Im dreading changing the finals lol > > T-Mobile. America's First Nationwide 4G Network. > > -----Original message----- > From: Don Wilhelm<w3...@embarqmail.com> > To: Mark Flavin<markf1...@hotmail.com> > Cc: elecraft@mailman.qth.net > Sent: Sat, Nov 26, 2011 17:45:04 GMT+00:00 > Subject: Re: [Elecraft] KPA100 Problem > > Mark, > > Have you checked the setting of the K2 CAL TPA menu? It should read the > same as the actual temperature of the PA transistor cases. > > Let everything acclimate to the ambient room temperature (power off for 30 > minutes should do it), then turn power on and set CAL TPA to the room > temperature in degC. > > 73, > Don W3FPR > > On 11/26/2011 11:44 AM, Mark Flavin wrote: >> >> >> Well, I wanted to change the bridge diodes in the KPA 100 cause I was > getting some wierd readings and hi swr readings so I decided to upgrade it > while I had it apart. I did the whole upgrade and now as soon as I put it > in high power, even at only 15 watts, I get PA HOT readings. I have checked > all the parts values twice and did the calibration again including the C6 > adjust, the r26 and 27 adjusts and even pulled the finals to make sure they > weren't shorted or anything. Q3 and Q4 seem fine and are not cracked. The > voltages seem to be fine and I readjusted R6 bias as per book. Whats wierd > is as soon as I hit the key, even at 15 watts the fan comes on with the > keying. A dot gives a short fan wiggle and an dash gives a loneger fan > activation. Eventually it comes on and then I get the PA HOT. The fan even > responds to my voice on SSB. I mean it comes on almost instantly. I have > checked the archives and am starting to suspect the finals. I put on new > pads on the transisto >> rs and checked it all twice. Resoldered all connections. All works > fine at 10 watts. Im sure Im missing something but I dont seem to be able > to find it. Any ideas where I can check before I order new finals and go > through that work again. Thanks MarkN5MF > > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
