Merlin, First a correction - the IF signal path into the AGC does not flow through D2, so removing it will not shut down the AGC, but rather will guarantee that AGC will always be present - the IF signal comes into the mixer on pin 1 while C10 effectively grounds pin 2 at the IF frequency.
I have not seen or heard of a failure for Control Board U2, but I guess it is possible - but before making any rash conclusions, can you provide the voltage measurements at U2 pins 5, 6 and 7? Also check the resistance measured from U2 pin 7 to pin 6 - if it is much greater than 33k, check the soldering at R5 and/or check for a bad R5. PS - yes I would like to see your KSB2 shielding. Can you put it on a website or something like that? - I'm certain we will need pictures. 73, Don W3FPR > -----Original Message----- > > Unrelated to the finals, I turned the K2 on and the S meter > pegged and the > receiver shut down its 1350P IF amp. I measured the AGC voltage. > It's way up > there at 5.5 volts, regardless of whether the AGC is disabled and > regardless > of the position of the RF gain control. Sure enough, if I lift the > collector on Q12, the receiver comes up to full sensitivity. If > I lift d2 (these are > all components on the control board, by the way), thus depriving > the AGC amp > of a signal from the IF, it still makes no difference; the AGC amplifier > still makes too much voltage. Any thoughts? Everything else > works, by the way. > Does U2 just go bad sometimes? > > By the way, in the matter of filters, I've come up with a simple > shielding > technique, using tin sheet from hobby shops, that actually improves the > ultimate rejection and the shape factor of the seven pole device > that's used in the > KSB2. > > I bet somebody out there has experienced this weirdness. I hope > > _______________________________________________ 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
