Someone, Don I think, posted a message this week suggesting that the background noise with no antenna connected should be the same with AGC either on or off. I checked mine out of curiosity and discovered that mine was quieter with AGC on.
Before making adjustments to R1, I thought I'd run through the AGC voltage checks in the manual to see what they looked like. With RF gain at maximum, pin 5 of U2 = 3.8vdc I turned to Troubleshooting/Signal Tracing (Appendix E, page11) and made the following measurements on the control board: Using the XG2 signal generator, 7040khz @ 50uv Test 1, XG2 off, RF Gain MAX U2 pin 1 = 3.41vdc - expected 3.6 Test 2, XG2 off, RF Gain MIN U2 pin 1 = 4.50vdc - expected 4.6 Test 3, XG2 on, RF Gain MIN U2 pin 1 = 4.50vdc - expected 6.9 (VFO adjusted for max) U2 pin 5 = 4.89vdc - expected 5.0 In test 3, U2 pin 1 is 2.5vdc too low. Just for grins, I compared the voltages on U2 pins 1 & 3 at various RF Gain settings and I found the same voltages on both pins; pin 1 seems to be tracking pin 3 accurately; I think this is OK. Using an RF probe, I measured the anode of D1 and found 65mv with XG2 off and 110mv with XG2 on, a 45mv swing. Using an DMM, I measured the cathode of D1 and found 4.73vdc with XG2 off and 4.86vdc with XG2 on. Q12 measures: C = 7.9vdc E = 4.5vdc B = 4.5vdc I'm inclined to believe Q12 may be defective. Before I order parts, though, thought I'd check with you folks and see if I'm even in the ball park. _______________________________________________ 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
