Re: [Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI
Hi The last K2 I built had strange AGC and S-meter operation that sounds like the one you are working on. The problem was I had skipped installing the toroid RFC11 on the bottom of the board. It is amazing the K2 worked at all but it received fairly well. I could even hear the 1 uV signal from the XG2. Anyway installing the RFC solved the problem. May be worth a look to see if you have the same problem Don Brown KD5NDB - Original Message - From: "Gerhard Schwanz" <[EMAIL PROTECTED]> To: Cc: <[EMAIL PROTECTED]> Sent: Friday, November 11, 2005 2:23 AM Subject: [Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI > Hi list, > hi all those who answered my first question. > > I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to > 3.65, > 3.72 and 3.8V. It got better for sure. The difference between AGC on and > off > is in all cases noticable, but slightly. But I think it's significant, > because... > > When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start > lighting. So I guess AGC sets in. And this should not be the case, I > guess? > Any idea? > > Have a nice day, > > Gerhard > > > - Original Message - > From: "Don Wilhelm" <[EMAIL PROTECTED]> > To: "GS" <[EMAIL PROTECTED]> > Sent: Wednesday, November 09, 2005 3:35 PM > Subject: RE: RE: [Elecraft] K2 receiver problem > > > > Gerhard, > > > > If you have a K2 with serial number greater than 3000, the AGC > > adjustment > > pot is on the Control Board near the right end - the designation is R1. > > > > For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor. > > Same procedure applies - change the value of R1 to set the AGC > > threshold. > > It is easy to substitute a temporary pot (50K will do fine) to make the > > adjustment - once the right value is found, solder in the closest value > > fixed resistor. > > > > In my experience, the fixed resistor that one would end up with will > > vary > > between 33K at the low end and 47k at the high end. > > > > BTW, if this receiver has worked properly before and suddenly developed > this > > problem, look more closely for a failed component - it will likely be in > the > > AGC area - see the control board schematic in the lower left corner. > > > > 73, > > Don W3FPR > > > > > -Original Message- > > > From: GS [mailto:[EMAIL PROTECTED] > > > Sent: Wednesday, November 09, 2005 9:48 AM > > > To: [EMAIL PROTECTED] > > > Subject: Ant: RE: [Elecraft] K2 receiver problem > > > > > > > > > Hi Don, > > > > > > I can't find how to set the AGC threshold for optimum > > > receiver sensitivity, neither in the manual nor is > > > there any hint in the circuit. At least not for me ;-) > > > > > > Only threshold mentioned in the manual is for the > > > NB... > > > > > > WHAT do I have to adjust to achieve max. voltage at U2 > > > pin 5, ctrl board? > > > > > > Thanks!!! > > > > > > Gerhard > > > > > > > > > --- Don Wilhelm <[EMAIL PROTECTED]> schrieb: > > > > > > > Gerhardt, > > > > > > > > It sounds like the AGC Threshold is not set > > > > properly. > > > > > > > > I would proceed by first checking the alignment of > > > > the bandpass filters in > > > > Transmit mode (at 2 watts) and then set the AGC > > > > Threshold for optimum > > > > receiver sensitivity - with no antenna connected and > > > > AF and RF Gains set to > > > > max, adjust for the highest voltage at Control Board > > > > U2 pin 5 which yields > > > > no change in the audio noise when switching the AGC > > > > between OFF and ON. > > > > That will usually result in a voltage in the range > > > > of 3.65 to 3.8 volts at > > > > U2 pin 5. Set the S-meter end points (CAL S Hi and > > > > CAL S-Lo) after setting > > > > the threshold. > > > > > > > > If that does not cure the problem, then look for a > > > > problem in the IF receive > > > > chain - that will be where the signal tracing is > > > > required, follow the > > > > p[rocedure for receiver signal tracing in the > > > > Troubleshooting appendix of > > > > the K2 manual. > > > > > > > > > > > > 73, > > >
[Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI
Hi list, hi all those who answered my first question. I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to 3.65, 3.72 and 3.8V. It got better for sure. The difference between AGC on and off is in all cases noticable, but slightly. But I think it's significant, because... When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start lighting. So I guess AGC sets in. And this should not be the case, I guess? Any idea? Have a nice day, Gerhard - Original Message - From: "Don Wilhelm" <[EMAIL PROTECTED]> To: "GS" <[EMAIL PROTECTED]> Sent: Wednesday, November 09, 2005 3:35 PM Subject: RE: RE: [Elecraft] K2 receiver problem > Gerhard, > > If you have a K2 with serial number greater than 3000, the AGC adjustment > pot is on the Control Board near the right end - the designation is R1. > > For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor. > Same procedure applies - change the value of R1 to set the AGC threshold. > It is easy to substitute a temporary pot (50K will do fine) to make the > adjustment - once the right value is found, solder in the closest value > fixed resistor. > > In my experience, the fixed resistor that one would end up with will vary > between 33K at the low end and 47k at the high end. > > BTW, if this receiver has worked properly before and suddenly developed this > problem, look more closely for a failed component - it will likely be in the > AGC area - see the control board schematic in the lower left corner. > > 73, > Don W3FPR > > > -Original Message- > > From: GS [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, November 09, 2005 9:48 AM > > To: [EMAIL PROTECTED] > > Subject: Ant: RE: [Elecraft] K2 receiver problem > > > > > > Hi Don, > > > > I can't find how to set the AGC threshold for optimum > > receiver sensitivity, neither in the manual nor is > > there any hint in the circuit. At least not for me ;-) > > > > Only threshold mentioned in the manual is for the > > NB... > > > > WHAT do I have to adjust to achieve max. voltage at U2 > > pin 5, ctrl board? > > > > Thanks!!! > > > > Gerhard > > > > > > --- Don Wilhelm <[EMAIL PROTECTED]> schrieb: > > > > > Gerhardt, > > > > > > It sounds like the AGC Threshold is not set > > > properly. > > > > > > I would proceed by first checking the alignment of > > > the bandpass filters in > > > Transmit mode (at 2 watts) and then set the AGC > > > Threshold for optimum > > > receiver sensitivity - with no antenna connected and > > > AF and RF Gains set to > > > max, adjust for the highest voltage at Control Board > > > U2 pin 5 which yields > > > no change in the audio noise when switching the AGC > > > between OFF and ON. > > > That will usually result in a voltage in the range > > > of 3.65 to 3.8 volts at > > > U2 pin 5. Set the S-meter end points (CAL S Hi and > > > CAL S-Lo) after setting > > > the threshold. > > > > > > If that does not cure the problem, then look for a > > > problem in the IF receive > > > chain - that will be where the signal tracing is > > > required, follow the > > > p[rocedure for receiver signal tracing in the > > > Troubleshooting appendix of > > > the K2 manual. > > > > > > > > > 73, > > > Don W3FPR > > > > > > > -Original Message- > > > > > > > > got a K2 from another OM on my workbench. It's got > > > a > > > > receiver problem and I just want to make sure I do > > > the > > > > checks in the correct order and I'm looking for > > > hints, > > > > if available! > > > > > > > > Thanks in advance! > > > > > > > > So here's the problem and what I want to do. It > > > seems > > > > the receiver runs with "handbrake on". So the > > > s-meter > > > > shows 3 bars without an antenna but the rf gain is > > > > fully clockwise. I can reduce signals to zero > > > (using > > > > RF gain) with this K2 which I can't using my own > > > K2. > > > > So mine has a higher sensitivity. > > > > > > > > Any idea what's wrong? > > > > > > > > What I want to do: > > > > - s-meter alignment > > > > - I.F. amplifier alignment > > > > - (maybe band pass alignment) > > > > - signal tracing receiver and synthesizer > > > > > > > > Kind regards > > > > > > > > Gerhard > > > > DH3FAW > > > > > > > > > > > > > > > > > > > > > > > > > > ___ > > Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - > > Hier anmelden: http://mail.yahoo.de > > > > > > -- > > No virus found in this incoming message. > > Checked by AVG Free Edition. > > Version: 7.1.362 / Virus Database: 267.12.8/163 - Release Date: 11/8/2005 > > > > > ___ Gesendet von Yahoo! Mail - Jetzt mit 1GB Speicher kostenlos - Hier anmelden: http://mail.yahoo.de ___ 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.):
