Re: [Elecraft] K2 Low transmit power after shut down
Mick, You cannot properly troubleshoot a problem like that with too many variables involved. In your case, you have the base K2, the KPA100 (even when bypassed), your antenna tuner, and your antenna involved - the problem could be with any one of them. The solution is to reduce that number down to one at a time. One thing your lack of receive tells me is that you are likely looking for an intermittent connection somewhere. The challenge is to find out where. First, physically remove the KPA100 from the base K2 and set it aside. Then connect the base K2 to a known good 50 ohm non-reactive dummy load. When that is done, see if you have good power output (the K2 display will be close to correct with the dummy load). Check at a range of powers. If it OK, then we can move on to the KPA100 for the next step - tell me that is the case and we can continue with that. If the power output of the base K2 has problems (I presume it will have low power at some power setting), then set the power knob to 5 watts and proceed to make the measurements of RF voltage at the points shown in Appendix A page 14, starting midway down the left column. Make the measurements in order. If the RF voltages are *higher* than those listed, that is *not* a problem. Tell us the first point where the RF voltages are substantially *lower* than that listed. That is the output of the failing stage. We don't have to know the voltages at the prior stages, just the one that is lower than expected. Once we have that information we can help you localize it to the failing component. 73, Don W3FPR On 6/28/2015 8:04 PM, Mick Hall wrote: Hi Working on my K2 with a long wire antenna and externalATU and my K2 shut down. Only working at 5 watts and an SWR of 2.1:1. I didn’t smell anything initially so I powered it backup. At first I couldn’t hear anything on any band and slowly the sound cameback, which was a bit strange. The lights on the ATU no longer indicated any output sostarted checking a bit more when I got a faint smell of fried component. Before removing any covers I started checking basicthings. S meter stopped registering any received signals, although all bandscould be heard at normal levels. The ATU can only handle 15 watts so I tested up to thisand found that when I dialled in up to 10 watts, It was indicating 0.5 watts. Icould hear the KPA100 switch in at 11 watts but anything up to 15 watts showeda max of 6 watts. I bypassed the KPA100 by powering it from the base K2power socket and the I had the same results. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] [K2] No Transmit Power
?Don: I am still trying to get my K2 kit to transmit. Since my last post, I have purchased a power meter and confirmed that virtually no power comes out of the antenna jack when the transceiver is keyed (the meter barely moves on the 20 watt scale). I also purchased a new RF probe kit and so far have the same dismal result: the lowest voltage I can measure (probing nothing) is 380 mV, and also 380mV when I attach the ground clip to the probe tip. Touching my finger to the probe tip gives no result as well. This probe was built with new components from Elecraft, the diode is in the way the silk screen indicates (for the banded end). there is no other way to build it! The only idea I have is to take the probe into work and check it with a nice new Fluke meter with the idea that my 2 multimeters are just not suitable or have the wrong input impedance (needs to be ~10Megohms if I understand the probe circuit). Without some way of measuring RF in the transmitter circuit I am just shooting in the dark. I attempted to check Q24 but it's solder joints are placed right under the small SMT board that is mounted on the backside of the RF board and difficult to reach unless I remove that board. Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelm d...@w3fpr.com To: Brian Denley b.den...@comcast.net Sent: Monday, September 20, 2010 6:23 PM Subject: Re: [Elecraft] [K2] No Transmit Power Brian, If there is nothing coming from the internal power detector, you will not see deflection on the K2 bargraph when keying. It could be a K2 transmit problem or it can be a problem in the RF detector. Hard to tell which without further measurements. 73, Don W3FPR __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, Did you use coax for the lead from the RF Probe to your DMM? Behavior like that indicates noise pickup after the detector diode - RF? Magnetic coupling? It is really difficult to say what, you will have to examine your environment as well as your meter. Yes, unless you can get the stray pickup (from whatever source) out of your DMM, you will have a difficult time doing any transmit signal tracing. Hint - take your DMM into work with you and do a 1 to 1 comparison in the same environment with another meter. If there is noise pickup on your meter at home, but not at your work location, having your DMM with you at work will reveal that condition. 73, Don W3FPR On 10/4/2010 10:18 PM, Brian Denley wrote: ?Don: I am still trying to get my K2 kit to transmit. Since my last post, I have purchased a power meter and confirmed that virtually no power comes out of the antenna jack when the transceiver is keyed (the meter barely moves on the 20 watt scale). I also purchased a new RF probe kit and so far have the same dismal result: the lowest voltage I can measure (probing nothing) is 380 mV, and also 380mV when I attach the ground clip to the probe tip. Touching my finger to the probe tip gives no result as well. This probe was built with new components from Elecraft, the diode is in the way the silk screen indicates (for the banded end). there is no other way to build it! The only idea I have is to take the probe into work and check it with a nice new Fluke meter with the idea that my 2 multimeters are just not suitable or have the wrong input impedance (needs to be ~10Megohms if I understand the probe circuit). Without some way of measuring RF in the transmitter circuit I am just shooting in the dark. I attempted to check Q24 but it's solder joints are placed right under the small SMT board that is mounted on the backside of the RF board and difficult to reach unless I remove that board. Brian Denley http://home.comcast.net/~b.denley/index.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
For getting to Q24 leads, yes the SMT diode gets in the way, but I have found that most builders have left the leads long enough to bend the board assembly up enough to allow access to the Q24 leads. That may or may not be the case with your construction, but I mention it just in case. Unsoldering one lead to swing it out of the way is not a big deal either. My preference is to unsolder the lead from the RF board (leaving it attached to the small board) - it is easier to re-install the diode that way. 73, Don W3FPR On 10/4/2010 10:18 PM, Brian Denley wrote: I attempted to check Q24 but it's solder joints are placed right under the small SMT board that is mounted on the backside of the RF board and difficult to reach unless I remove that board. Brian Denley http://home.comcast.net/~b.denley/index.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, Yes, Elecraft has a repair service. If you contact sa...@elecraft.com, you should be able to obtain the necessary forms and an RSA number. If they ask you if you have tried contacting support, you can try telling them that you have been working with my suggestions. 73, Don W3FPR On 9/19/2010 10:26 PM, Brian Denley wrote: ?I am just about at the end of my rope trying to get this K2 to transmit. Nothing is coming out of the transmitter because nothing seems to be going into the PA circuit. The receiver circuits all work fine. All RF board transistors and diodes check out fine as far as DC is concerned but my RF probe does not function and I am unable to find the fault. I suspect the T/R switch or whatever circuit generates the RF signal in the first place but the trouble shooting help in the manual does not go yery deep on those issues. What is my next step? Does Elecraft offer a repair service? I have been at this for 4 weeks now with no progress at all. Thanks Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelmw3...@embarqmail.com To: Brian Denleyb.den...@comcast.net Cc: Elecraft Reflectorelecraft@mailman.qth.net Sent: Tuesday, September 07, 2010 11:08 PM Subject: Re: [Elecraft] [K2] No Transmit Power On 9/7/2010 10:16 PM, Brian Denley wrote: Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 voltsthis is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW 7.)Driver Input (base of Q6):34 mV 8.)Driver Output (collector of Q6):179 mVthis is VERY LOW 9.)PA Inputy (base of Q7):80 mV this seems HIGH 10.)PA input (base of Q8):80 mV this seems HIGH 11.)RF Detector Input (anode of D9):143 mV this is VERY LOW on my own I also measured: 12.)base of Q5:43 mV 13.)out of C10743 mV all of the DC voltages in column 1 on page 17 are normal __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, DON'T DO THAT! If the K2 is developing any power, it will not do it for long without a 50 ohm dummy load. The PA transistors can go poof in a hurry when operated into an open circuit - yes, the small antenna wire is an open circuit. 73, Don W3FPR On 9/19/2010 10:39 PM, Brian Denley wrote: ?I should add: If I connect a small wire to my K2 antenna and press tune, it shows a strong signal on any of my receivers at that frequency. So somethings coming out of the K2. Either the ouput signal is low OR the K2 RF detector just doesn't measure it correctly for the ALC circuit. Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Brian Denleyb.den...@comcast.net To:d...@w3fpr.com Cc: Elecraft Reflectorelecraft@mailman.qth.net Sent: Sunday, September 19, 2010 10:26 PM Subject: Re: [Elecraft] [K2] No Transmit Power ?I am just about at the end of my rope trying to get this K2 to transmit. Nothing is coming out of the transmitter because nothing seems to be going into the PA circuit. The receiver circuits all work fine. All RF board transistors and diodes check out fine as far as DC is concerned but my RF probe does not function and I am unable to find the fault. I suspect the T/R switch or whatever circuit generates the RF signal in the first place but the trouble shooting help in the manual does not go yery deep on those issues. What is my next step? Does Elecraft offer a repair service? I have been at this for 4 weeks now with no progress at all. Thanks Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelmw3...@embarqmail.com To: Brian Denleyb.den...@comcast.net Cc: Elecraft Reflectorelecraft@mailman.qth.net Sent: Tuesday, September 07, 2010 11:08 PM Subject: Re: [Elecraft] [K2] No Transmit Power On 9/7/2010 10:16 PM, Brian Denley wrote: Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 volts this is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW 7.)Driver Input (base of Q6):34 mV 8.)Driver Output (collector of Q6):179 mVthis is VERY LOW 9.)PA Inputy (base of Q7):80 mV this seems HIGH 10.)PA input (base of Q8):80 mV this seems HIGH 11.)RF Detector Input (anode of D9):143 mV this is VERY LOW on my own I also measured: 12.)base of Q5:43 mV 13.)out of C10743 mV all of the DC voltages in column 1 on page 17 are normal __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
?I am just about at the end of my rope trying to get this K2 to transmit. Nothing is coming out of the transmitter because nothing seems to be going into the PA circuit. The receiver circuits all work fine. All RF board transistors and diodes check out fine as far as DC is concerned but my RF probe does not function and I am unable to find the fault. I suspect the T/R switch or whatever circuit generates the RF signal in the first place but the trouble shooting help in the manual does not go yery deep on those issues. What is my next step? Does Elecraft offer a repair service? I have been at this for 4 weeks now with no progress at all. Thanks Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelm w3...@embarqmail.com To: Brian Denley b.den...@comcast.net Cc: Elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, September 07, 2010 11:08 PM Subject: Re: [Elecraft] [K2] No Transmit Power On 9/7/2010 10:16 PM, Brian Denley wrote: Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 voltsthis is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW 7.)Driver Input (base of Q6):34 mV 8.)Driver Output (collector of Q6):179 mVthis is VERY LOW 9.)PA Inputy (base of Q7):80 mV this seems HIGH 10.)PA input (base of Q8):80 mV this seems HIGH 11.)RF Detector Input (anode of D9):143 mV this is VERY LOW on my own I also measured: 12.)base of Q5:43 mV 13.)out of C10743 mV all of the DC voltages in column 1 on page 17 are normal __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
?I should add: If I connect a small wire to my K2 antenna and press tune, it shows a strong signal on any of my receivers at that frequency. So somethings coming out of the K2. Either the ouput signal is low OR the K2 RF detector just doesn't measure it correctly for the ALC circuit. Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Brian Denley b.den...@comcast.net To: d...@w3fpr.com Cc: Elecraft Reflector elecraft@mailman.qth.net Sent: Sunday, September 19, 2010 10:26 PM Subject: Re: [Elecraft] [K2] No Transmit Power ?I am just about at the end of my rope trying to get this K2 to transmit. Nothing is coming out of the transmitter because nothing seems to be going into the PA circuit. The receiver circuits all work fine. All RF board transistors and diodes check out fine as far as DC is concerned but my RF probe does not function and I am unable to find the fault. I suspect the T/R switch or whatever circuit generates the RF signal in the first place but the trouble shooting help in the manual does not go yery deep on those issues. What is my next step? Does Elecraft offer a repair service? I have been at this for 4 weeks now with no progress at all. Thanks Brian Denley http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelm w3...@embarqmail.com To: Brian Denley b.den...@comcast.net Cc: Elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, September 07, 2010 11:08 PM Subject: Re: [Elecraft] [K2] No Transmit Power On 9/7/2010 10:16 PM, Brian Denley wrote: Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 volts this is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW 7.)Driver Input (base of Q6):34 mV 8.)Driver Output (collector of Q6):179 mVthis is VERY LOW 9.)PA Inputy (base of Q7):80 mV this seems HIGH 10.)PA input (base of Q8):80 mV this seems HIGH 11.)RF Detector Input (anode of D9):143 mV this is VERY LOW on my own I also measured: 12.)base of Q5:43 mV 13.)out of C10743 mV all of the DC voltages in column 1 on page 17 are normal __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 voltsthis is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW 7.)Driver Input (base of Q6):34 mV 8.)Driver Output (collector of Q6):179 mVthis is VERY LOW 9.)PA Inputy (base of Q7):80 mV this seems HIGH 10.)PA input (base of Q8):80 mV this seems HIGH 11.)RF Detector Input (anode of D9):143 mV this is VERY LOW on my own I also measured: 12.)base of Q5:43 mV 13.)out of C10743 mV all of the DC voltages in column 1 on page 17 are normal Anything look new? Thanks for any help!! Brian http://home.comcast.net/~b.denley/index.html - Original Message - From: Don Wilhelm w3...@embarqmail.com To: Brian Denley b.den...@comcast.net Cc: Elecraft Reflector elecraft@mailman.qth.net Sent: Tuesday, September 07, 2010 12:59 AM Subject: Re: [Elecraft] [K2] No Transmit Power Brian, Since you are unable to measure any RF voltage, I am going to start at the beginning - proper assembly of the RF Probe. The RF probe voltage is not read across the 4.7 meg resistor, it is read between the end of the 4.7 meg resistor and ground. That is an important difference. In other words, the 4.7 megohm resistor is in series with the detector. Since the nominal input resistance of a DMM is 11 megohms (established in the old days of VTVMs), that resistance in series with the 11 megohms will cause the DMM to indicate the RMS value of the RF voltage being measured. There are other techniques that will provide DMM readings that indicate the zero to peak RF voltage, but the RF probe parts provided with the K2 will indicate the RMS voltage values when used with most DMMs. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, VPWR is high because there is not enough output being sensed by the RF detector, and the K2 firmware is telling the control circuit to add more power. With that fact in mind, there does not seem to be sufficient RF voltage at the Xmit Mixer Output, and the other points beyond it as well - but we will come back to those at a later time if necessary. You are correct that the Pre-driver output is the first point significantly lower than the expected value (and all measurements beyond that add no further value at this time), so the Q5 circuit is the one to investigate. I would suggest temporarily removing T3 to remove the 12 volts from Q7 and Q8 and gives you the ability to safely make measurements without the heat sink installed (Do NOT transmit with the heat sink removed and 12 volts connected to the collectors of Q7 and Q8 - the PA transistors will fry quickly). The first thing would be to make DC measurements at Q5 and compare with the chart in the manual. If nothing looks awry with those measurements, then look at the schematic and find all components in the Q5 stage - examine each one for proper values, good soldering - even to the point of arbitrarily re-flowing the solder with a hot soldering iron (750 deg/F). Add a wee bit of solder during the re-flow process to add some additional flux. If there is a blob of solder on any connections already, wick the excess away and then resolder with a smaller amount. Most new build problems turn out to be soldering problems, followed by toroid lead tinning and by component mis-placement. Those components jump out of their proper holes and get soldered into the wrong places :-) . 73, Don W3FPR On 9/7/2010 10:16 PM, Brian Denley wrote: Don: I brought home a DSO5054A (very nice 500 MHz Agilent scope!) and I was able to take the better measurements. My measurements were in P-to-P but I have divided them by 2.8 for RMS comparison:\ (all measurments Keydown) 1.)VPWR line (pin 2 of U8 on control board):5.0 voltsthis is HIGH 2.)Xmit Mixer Output (pin 4 of U10):28 mV 3.)Buffer Output (pin 6 of U9):121 mV 4.)Band-Pass Filter Output (W6):42 mV 5.)T-R Switch #1 Output (anode of D1):41 mV 6.)Pre-Driver Output (collector of Q5):34 mV this seems LOW __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, Since you are unable to measure any RF voltage, I am going to start at the beginning - proper assembly of the RF Probe. The RF probe voltage is not read across the 4.7 meg resistor, it is read between the end of the 4.7 meg resistor and ground. That is an important difference. In other words, the 4.7 megohm resistor is in series with the detector. Since the nominal input resistance of a DMM is 11 megohms (established in the old days of VTVMs), that resistance in series with the 11 megohms will cause the DMM to indicate the RMS value of the RF voltage being measured. There are other techniques that will provide DMM readings that indicate the zero to peak RF voltage, but the RF probe parts provided with the K2 will indicate the RMS voltage values when used with most DMMs. The RF Probe parts and board that were provided with your K2 kit should give you the correct connections and RF voltage readings. The TIP should connect to whatever wire you choose to use for the probe tip - I suggest one of the heavy diode leads so it is physically sturdy enough to be pressed onto the point to be measured. The ground wire (with the alligator clip) should connect to the ground symbol point near the tip with a 4 to 6 inch wire and the alligator clip on the far end. The coax should be connected as indicated on the board silkscreen - the shield to ground and the center conductor connects to the end of the 4.7 ohm resistor (follow the PC trace on the board). At the far end of the coax, the red banana plug connects to the center conductor of the coax and the shield connects to the black - you should use a 4 inch length of wire between the shield and the black banana plug. The schematic on page 9 of Appendix E shows which is connected to what. The banana plugs connect to your DMM, and the DMM will read the RMS value of a sinewave that is probed by the tip (the alligator clip must be connected to one of the ground loops that you should have installed on your K2 RF board). I cannot discern from you postings whether you have things set up correctly to measure RF voltages correctly or not. An oscilloscope can be used in place of the RF Probe, but it must be used with a 10X probe (the voltage readings must be corrected for the 10 times attenuation of the probe), and the expected values listed in the manual must be massaged because the 'scope will show you peak to peak voltages which are 2.8 times the RMS values listed in the manual. 73, Don W3FPR On 9/6/2010 10:28 PM, Brian Denley wrote: Don: I am officially stumped. I cannot find the fault in my transmit circuit but that is basically do to my inability to accurately measure ANY RF voltage. The RF probe doesn't seem to function. I have replaced the resistor and resoldered all the connections twice now but I continue to read betwen 50 and 70 mV with any handheld DMM and basically nothing with an HP3478A, I am using the DC volt setting. And all that 50 to 70 mV is across the 4.7Mohm resistor on the probe board. This reading masks almost anything I am trying to measure and without that capability, I am at a loss trying to trouble shoot the transceiver. Connecting the ground lead to the probe still leaves me with the same reading. Is there any other instrument that I can buy or borrow that will accurately measure small RF voltages? Can I buy a working RF probe from Elecraft? Are there only certain DMMs that it will work with? Again, the receiver section and the panel and control functions work just fine but I only get about 0.5 mW on the readout with keydown. Brian Denley http://home.comcast.net/~b.denley/index.html Brian, Yes, I am sure about the 4.7 Megohms, but your 4.6 meg resistor will do just as well. It is DC voltage through the resistor, and it scales the peak RF voltage down to approximate RMS. Look at the schematic for the RF Probe on page 9 of Appendix E in the K2 manual. With the RF Probe, you will be able to measure RF voltages down into the millivolt region. Go through the steps listed in Appendix E of the manual under Transmit Signal Tracing. When you get to the points to measure on page 14 (assuming you do not find a problem with the VFO or BFO), the RF voltages will be HIGHER than the expected value because you do not have enough transmit output. What you are looking for is the first point where the RF voltage is LOWER than the expected value. That point is just beyond the failing stage, and you will know which stage to examine in detail. Only after your K2 is operating properly for RF output will you see the expected values - go with the higher or lower criteria. Don __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email
Re: [Elecraft] [K2] No Transmit Power
Brian, Are you certain you have nor swapped the collector and emitter voltages for Q11? Refer to the Schematic Key page for the proper leads - be certain you are keep the device orientation correct. Yes, the DC voltages on Q5 seem to be correct, but your prior RF voltages say that the Q5 stage is not working properly. Check all the components in the Q5 stage, including T1. Check the leads of T1 carefully. If you can see a circle around any lead, the solder did not adhere properly due to an improperly tinned lead. If there is evidence of that condition, you will have to remove T1 and re-tin the leads. 73, Don W3FPR On 9/1/2010 10:57 PM, Brian Denley wrote: Don: The Key Down voltages on Q5 were completely normal: E: 0.547 V B: 1.274 V C: 10.26 (12.0 volt power supply) I also checked the voltages from D1 through Q11 (page 17 or Appendix F) and they are vall OK except that the base voltages from Q6, Q7 and Q8 are close to zero when they should read 1.1, 0.6 and 0.6 Volts respectively. It seems Q5 is working OK but how do I know any signal is comping into that amplifier? The only oddity I have run into is that I read the opposite voltages for Q11 than the manula states i.e I got: E: 1.2 V B: 0.6 V C: 0 This was with key down. I have stared at the device again and again to see if I am reading it backwards but I cannot find my error so far. Thanks for any help. Brian http://home.comcast.net/~b.denley/index.html __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [K2] No Transmit Power
Brian, On your RF Probe, that 200 mV is noise pickup. Do you have a relatively short ground wire (4 to 6 inches) with the alligator clip connected to the board near the tip? That alligator clip should connect to one of the ground loops you installed on the K2 boards. A short grounding wire like that should reduce the noise pickup level - if it does not, check the soldering. The DMM reading should go to a very low millivolt level when the ground wire and the tip are connected together. If you have a 'scope, it will give you good readings if you use a 10X probe and both the probe and 'scope have adequate frequency ratings for the frequency in use. In general, a 'scope and probe can be used for reliable amplitude measurement if their frequency rating is 5 times the frequency of the signal. It is still usable above that frequency for relative RF voltage measurements. Remember that the 'scope will display the peak to peak amplitude (the RF Probe will indicate RMS values), so multiply the 'expected' voltages in the manual by 2.8 to obtain the corresponding peak to peak amplitude. Regarding the DC voltage at CB U8 pin 2, read the entire paragraph carefully. it is high because your K2 power output is lower than the requested value (reason a of the two reasons listed). Since you have checked the RF Detector, go to the end of the paragraph and do what it says If you can't find a problem with the RF Detector, continue with the next signal tracing section (transmit mixer, etc). Check the Transmit stages in the order listed - if the stage is working, the RF Voltage will be HIGHER than the expected value listed (that stage is trying to drive harder to increase the power output). When you come to the stage where the RF Voltage is significantly lower than the expected value, that is the output of the stage with the problem - stop and analyze that stage - Do the DC Voltage measurements associated with that stage, then move on to the schematic armed with that voltage information and see which component is likely to cause that problem. Hint: it is usually NOT the transistor. That process is consistent with the 3 steps for any generalized troubleshooting process. 1) Find the failing stage. 2) Make measurements of that stage 3) Analyze the circuit to determine what is causing abnormalities in the measurements. 73, Don W3FPR On 8/27/2010 11:41 PM, Brian Denley wrote: I have built the RF probe but I am unable to get any signal less than about 200 mV even when not touching anything. I have tried three DMMMs with no better luck. I do know that I am transmitting something because I can pick up the transceiver signal easily on any of my HF receivers. I have been able to establish that pin 2 of U8 on the Control Board reads 5.0 volts key down and that means (according to page 14) that I should check the components around the RF detector...and I will as soon as I can find a way sense RF. Maybe I will switch to the scope tomorrow and try that. Any other ideas will be welcome. BTW, I have checked the RF detector again and again. It's a pretty simple circuit and the diode is oriented correctly. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
