Pat, One further check - RFC7 (15 uH) and C104 (68 pF). This is a series resonant circuit tuned approximately to the IF frequency - if for some reason these 2 components are series resonant somewhere around 12 mHz, it could reduce the 30 and 20 meter signals significantly. As a quick check, you could lift one end of RFC7 and see if you can tune the bandpass on 30 and 20.
73, Don W3FPR > -----Original Message----- > > Over the weeks now of troubleshooting this problem here are some of the > steps I have taken: > > * I suspected either a defective low pass filter or bandpass > filter for this band and one other. (I had damaged K7 with a soldering > iron that > put an ever-so-small dimple in one end of the relay case. > This prevented the slide from fully engaging one set of contacts. I > replaced it and > that band was then okay.) After replacing the defective relay > I lifted one end of W1 to isolate the two sections of filters and hooked > a > signal generator to the antenna connection. I hooked my > scope to W1 and found all low pass filter characteristics as one would > expect, > no loss of signal strength on the selected band but noticeable > attenuation on the next higher band. I forgot to say that I had already > reflowed all solder connections on both the LPF and BPF > circuits. > > * I replaced C22 (2.7 pF). > > * I hooked a jumper to the BPF test point (I had soldered a loop > of wire onto D7 cathode to prevent damaging the component leads with > my scope probe) and could hear stations on both 20 and 30 > meters. I coupled this lead through a capacitor (to prevent shorting 8R) > and > the signals were as loud on the two bands in question as the > other, functional bands. > > * My friend Ron used a high quality capacitance / inductance > meter and found L9 to vary from, as I recall, about 3.9~4.9 uH with the > slug > top to bottom. The capacitors in circuit measured > approximately their stamped values considering stray circuit > capacitances. Each of us > checked and rechecked the values of all components and they > were correct. Neither capacitors nor inductor were shorted to ground > except the ends of caps that were supposed to be. > > * I have measured contacts 2,3,4 and 7,8,9 on relays K3 and K4 > and they function as you would expect from the relay truth table. I even > > tried a relay reset (control board removed on power up) and > then rechecked with identical results. I also have cheched that the > signal line > (W1, W6 and BPF T.P.) is not shorted to ground on 20/30. > > * When feeding a signal from my sig generator through the coax > connector and checking at the BPF T.P. there is no noticeable attenuation > > on any bands except 20 and 30 which was down about 70 dB. > > * L8 peaks properly on 30 meters. With the added cap acrross L9 > it peaks about two turns from the top of the can. > > At this point I had already decided to arbitrarily replace C24 and C25 > but I don't really expect any change since they check okay with a > capacitance meter in circuit. (C19 and C20 check the same as C24 and > C25). I am really getting discouraged at this point, but like Little > Orphan Annie sings, "The sun will come out tomorrow!" Thanks to all for > your suggestions. If I have an epiphany, I'll let you know! > > 73, > > Pat-K4BEH > _______________________________________________ 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
