Re: [Elecraft] Setting the AGC Threshold on K2
Hello Jeff, Have you tried measuring the voltage at the wiper terminal of R1 (Control Board) or RP6 pins 4/5? These points are all connected together along with U2 pin 5, so you should get the same voltage +- a couple of millivolts at each of these points. The voltage at all these points should vary but remain equal as you tweak R1 and be .002V, approx 3.8V downwards. However your .002 volt reading makes me wonder whether or not the probe is actually making contact with U2 pin 5 or is sitting on top of a layer of gunge that has formed on the IC's pin e.g. corrosion. 73, Geoff GM4ESD jrb [EMAIL PROTECTED] wrote on December 18, 2005 at 1128 PM I've just completed the first alignment and test and everything checks out except setting the AGC threshold. When I put the probe of my DMM on pin 5 of U2 (a hellish place to get consistent readings) and adjust R1 I get only .002 DC volts. I've resoldered the pins on both U2 and R1. I've looked through Troubleshooting and the Reflector and haven't found anything relevant. By the way I had no trouble with the S-Meter alignment which is dependent on the AGC threshold. Is there any place else I should look on the control board for a possible source of trouble, or could U2 or R1 be defective? (I know components are rarely defective). ___ 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
RE: [Elecraft] Setting the AGC Threshold on K2
Jeff, Try measuring the voltage at U2 pin 5 again making certain your probes both have good contact. The voltage at U2 pin 5 is determined only by a resistor network - if it is still quite low, check the voltage on the 8A line - the output of regulator U4 (upper leg) - it should be 8 volts. If you have 8 volts at U4, then check and re-check the soldering of Control Board RP6, R1 and U2, then remeasure. Remember that the voltage is determined only by a resistive network (which includes the RF Gain pot), there are no active components involved, so if the voltages to the resistors and the connections are proper, you should achieve the correct voltage for the AGC Threshold. Be aware that the voltage for the AGC Threshold may not be optimum for your K2. After your K2 is fully built, aligned, and everything is working properly, you can optimize the AGC Threshold so that the AGC does not become active with no signal into the K2 antenna - so don't be concerned if the 3.8 volts is near the upper limit, I find that the optimum setting will vary from a low of 3.65 volts to a high of 3.78 volts. 73, Don W3FPR -Original Message- I've just completed the first alignment and test and everything checks out except setting the AGC threshold. When I put the probe of my DMM on pin 5 of U2 (a hellish place to get consistent readings) and adjust R1 I get only .002 DC volts. I've resoldered the pins on both U2 and R1. I've looked through Troubleshooting and the Reflector and haven't found anything relevant. By the way I had no trouble with the S-Meter alignment which is dependent on the AGC threshold. Is there any place else I should look on the control board for a possible source of trouble, or could U2 or R1 be defective? (I know components are rarely defective). TIA, Jeff KG6ZVT ___ 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
Re: [Elecraft] Setting the AGC Threshold on K2
Don I worked with him last night, he has it all going it was a cold solder joint on RP6 so he didn't have the 8 volt line. He's got it working nowwe emailed off the list. (Sometimes I forget to hit the reply all.) Gregg R. Lengling, W9DHI, Un-Retired K2/100 SN 3075 http://www.milwaukeehdtv.org - Original Message - From: Don Wilhelm [EMAIL PROTECTED] To: jrb [EMAIL PROTECTED]; elecraft@mailman.qth.net Sent: Monday, December 19, 2005 7:45 AM Subject: RE: [Elecraft] Setting the AGC Threshold on K2 Jeff, Try measuring the voltage at U2 pin 5 again making certain your probes both have good contact. The voltage at U2 pin 5 is determined only by a resistor network - if it is still quite low, check the voltage on the 8A line - the output of regulator U4 (upper leg) - it should be 8 volts. If you have 8 volts at U4, then check and re-check the soldering of Control Board RP6, R1 and U2, then remeasure. Remember that the voltage is determined only by a resistive network (which includes the RF Gain pot), there are no active components involved, so if the voltages to the resistors and the connections are proper, you should achieve the correct voltage for the AGC Threshold. Be aware that the voltage for the AGC Threshold may not be optimum for your K2. After your K2 is fully built, aligned, and everything is working properly, you can optimize the AGC Threshold so that the AGC does not become active with no signal into the K2 antenna - so don't be concerned if the 3.8 volts is near the upper limit, I find that the optimum setting will vary from a low of 3.65 volts to a high of 3.78 volts. 73, Don W3FPR -Original Message- I've just completed the first alignment and test and everything checks out except setting the AGC threshold. When I put the probe of my DMM on pin 5 of U2 (a hellish place to get consistent readings) and adjust R1 I get only .002 DC volts. I've resoldered the pins on both U2 and R1. I've looked through Troubleshooting and the Reflector and haven't found anything relevant. By the way I had no trouble with the S-Meter alignment which is dependent on the AGC threshold. Is there any place else I should look on the control board for a possible source of trouble, or could U2 or R1 be defective? (I know components are rarely defective). TIA, Jeff KG6ZVT ___ 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 ___ 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
