Re: [Elecraft] K3 died again and fixed
If you are doing hand solder replacements of SMD capacitors you should make sure you follow procedures to either pre-heat the component or take extreme precautions to guarantee that the soldering iron does not touch the capacitor electrodes. Thermal shock with cause the metal endcaps to crack the ceramic which will eventually cause high leakage or shorts in the capacitor. Seeing that you have found two SMD caps on the same board have failed then I am suspicious of the fabrication of this particular board. You might want to reference There are other stresses that can cause the capacitor to crack and fail such as board bending or contaminants under the part, BUT for home lab work the primary reason is thermal shocking during hand solder. de Dave K5MWR On 11/14/2019 00:37, Martin Sole wrote: A few days ago I posted the below message but had not had time until today to dig a little deeper. I took as my starting point the loss of both receive and transmit as an indicator that the culprit would likely be something common to both and given the lack of receiver noise whilst the P3 panadaptor showed normal signals and band noise suggested it would be after the first conversion. This suggested something in the second LO as a likely possibility and with the first intent being to measure the oscillator signals. I used my SDRplay RSP1 with the Steve Andrews spectrum analyser software as this was handy and is easy to use. BTW, this is a great tool if you have any of the RSP devices. Going to the KREF3 board between the synthesisers and probing the 49.380MHz reference showed a healthy signal close to 0dBm, as expected since the P3 confirmed tuning works, so I moved to the output of U2 the divide by 6, hmm, nothing, nada, zilch. Worries of a dead 74VHC175 with no replacement on hand was the first thought but rapidly followed by my knowledge that this board had not so long ago suffered a capacitor failure causing loss of the 7 volt transmit bias. With the KREF3 on the bench a quick measure from the 5 volt line to ground showed 82 ohms after L2, 87 ohms between L1 and L2 and about 91 before L1. Way too low for sure. There are 3 components here C7, C19 and U1. Having had a 0.1uF fail on this board already I was ready to bet the farm on either C7 or C19. C19 was the first to be removed and I hit pay dirt right off, shoulda bought that lottery ticket today! Another dud 0.1uF then. Measuring the 5v to ground showed it now at a much more respectable 1.3k ohms. Replacement was with a 1206 0.1 as I had done earlier with C6. Normal service is resumed. It's all back working as it should but I do wonder now about the possible longevity of the other 0.1uF capacitors both on this board and possibly in other parts of the radio. I count 12 more on this board alone. I should mention that my K3 is an early unit, S/N 298 so I presume circa 2008-ish. More than 10 years is not bad in my book and the faults have been fairly straight forward. It might be surface mount but it's eminently repairable. Martin, HS0ZED On 12/11/2019 19:48, Martin Sole wrote: Hi, My K3 is quite an early unit, S/N 298. Recently upgraded with new synths KRX3A and KXV3, I also have a P3 connected to the radio. A while back it failed with a shorted smd capacitor on the K3REF board causing loss of TX bias voltage. Today it has lost both receive and transmit and I am thinking it might be from the same module. Here's the situation. Rig powers on and appears to work normally except soft noise from the speaker, no band noise to speak of and no signals. P3 shows plenty of signals, S9 plus on FT8 freqs but nothing heard other than soft noise. Tuning works as signals move in the band scope. No sub receiver signals either and no TX output. Have not checked transverter output but expect to find nothing there. P3 take off at IF output so everything is clearly working up to there. DSP seems to be working as width and shift cause the expected changes in audio. S meter reads dead zero, no movement. About the only common point I can see is the K3REF board so it would appear a second failure on this module. Since this is where I had to do earlier work I wouldn't put it past being a user inflicted fault, but that repair was a month or more ago. Anyone care to have a guess or share thoughts? Martin, HS0ZED Earlier Hi, So I had some success in fixing this and thought I would write it up here briefly for future reference. Short version C6 on the K3REF module had become a 12 ohm resistor. Longer version Finding the 7T line only going to 3.5 volts or so was suspicious. Measuring the resistance to ground of that line showed about 20 ohms where the 7 volts is generated at U11 on the RF board, very suspicious. The first step then was to remove any removable item that has a connection to the 7T line. That's most modules in the K3. Checking the resistance of the 7T line each time I removed a plug
Re: [Elecraft] K3 died again and fixed
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Re: [Elecraft] K3 died again and fixed
A few days ago I posted the below message but had not had time until today to dig a little deeper. I took as my starting point the loss of both receive and transmit as an indicator that the culprit would likely be something common to both and given the lack of receiver noise whilst the P3 panadaptor showed normal signals and band noise suggested it would be after the first conversion. This suggested something in the second LO as a likely possibility and with the first intent being to measure the oscillator signals. I used my SDRplay RSP1 with the Steve Andrews spectrum analyser software as this was handy and is easy to use. BTW, this is a great tool if you have any of the RSP devices. Going to the KREF3 board between the synthesisers and probing the 49.380MHz reference showed a healthy signal close to 0dBm, as expected since the P3 confirmed tuning works, so I moved to the output of U2 the divide by 6, hmm, nothing, nada, zilch. Worries of a dead 74VHC175 with no replacement on hand was the first thought but rapidly followed by my knowledge that this board had not so long ago suffered a capacitor failure causing loss of the 7 volt transmit bias. With the KREF3 on the bench a quick measure from the 5 volt line to ground showed 82 ohms after L2, 87 ohms between L1 and L2 and about 91 before L1. Way too low for sure. There are 3 components here C7, C19 and U1. Having had a 0.1uF fail on this board already I was ready to bet the farm on either C7 or C19. C19 was the first to be removed and I hit pay dirt right off, shoulda bought that lottery ticket today! Another dud 0.1uF then. Measuring the 5v to ground showed it now at a much more respectable 1.3k ohms. Replacement was with a 1206 0.1 as I had done earlier with C6. Normal service is resumed. It's all back working as it should but I do wonder now about the possible longevity of the other 0.1uF capacitors both on this board and possibly in other parts of the radio. I count 12 more on this board alone. I should mention that my K3 is an early unit, S/N 298 so I presume circa 2008-ish. More than 10 years is not bad in my book and the faults have been fairly straight forward. It might be surface mount but it's eminently repairable. Martin, HS0ZED On 12/11/2019 19:48, Martin Sole wrote: Hi, My K3 is quite an early unit, S/N 298. Recently upgraded with new synths KRX3A and KXV3, I also have a P3 connected to the radio. A while back it failed with a shorted smd capacitor on the K3REF board causing loss of TX bias voltage. Today it has lost both receive and transmit and I am thinking it might be from the same module. Here's the situation. Rig powers on and appears to work normally except soft noise from the speaker, no band noise to speak of and no signals. P3 shows plenty of signals, S9 plus on FT8 freqs but nothing heard other than soft noise. Tuning works as signals move in the band scope. No sub receiver signals either and no TX output. Have not checked transverter output but expect to find nothing there. P3 take off at IF output so everything is clearly working up to there. DSP seems to be working as width and shift cause the expected changes in audio. S meter reads dead zero, no movement. About the only common point I can see is the K3REF board so it would appear a second failure on this module. Since this is where I had to do earlier work I wouldn't put it past being a user inflicted fault, but that repair was a month or more ago. Anyone care to have a guess or share thoughts? Martin, HS0ZED Earlier Hi, So I had some success in fixing this and thought I would write it up here briefly for future reference. Short version C6 on the K3REF module had become a 12 ohm resistor. Longer version Finding the 7T line only going to 3.5 volts or so was suspicious. Measuring the resistance to ground of that line showed about 20 ohms where the 7 volts is generated at U11 on the RF board, very suspicious. The first step then was to remove any removable item that has a connection to the 7T line. That's most modules in the K3. Checking the resistance of the 7T line each time I removed a plug in module showed the fault to be somewhere on the K3REF module. The 7T line on this board goes to Q3 via R16, R8 and R9 and also to Q2 and U3 via L5. Measuring either side of L5 showed lower resistance on the Q2 and U3 side, now around 12 ohms as opposed to 14 or so at pin 3 of P75. Focus then was directed at Q2 and U3 as likely culprits being active devices likely more prone to failure but removing Q2 showed no change nor did very carefully lifting pin8 of U3 and confirming no connection to L5. That left C6 as the remaining component on that line and its removal restored a much healthier 2.7k resistance to ground on that line as formed by R16, R8 and R9 around Q3 noted above. I don't have any of the microscopic 0.1uF capacitors used in this location, are they 0402? but I have a good selection of
Re: [Elecraft] K3 died again
Martin, I recommend you email supp...@elecraft.com because the support folks have handy access to the K3 techs if they are not able to diagnose the problem themselves, and can best assist you with the analysis. 73, Don W3FPR On 11/12/2019 7:48 AM, Martin Sole wrote: Hi, My K3 is quite an early unit, S/N 298. Recently upgraded with new synths KRX3A and KXV3, I also have a P3 connected to the radio. A while back it failed with a shorted smd capacitor on the K3REF board causing loss of TX bias voltage. Today it has lost both receive and transmit and I am thinking it might be from the same module. Here's the situation. Rig powers on and appears to work normally except soft noise from the speaker, no band noise to speak of and no signals. P3 shows plenty of signals, S9 plus on FT8 freqs but nothing heard other than soft noise. Tuning works as signals move in the band scope. No sub receiver signals either and no TX output. Have not checked transverter output but expect to find nothing there. P3 take off at IF output so everything is clearly working up to there. DSP seems to be working as width and shift cause the expected changes in audio. S meter reads dead zero, no movement. About the only common point I can see is the K3REF board so it would appear a second failure on this module. Since this is where I had to do earlier work I wouldn't put it past being a user inflicted fault, but that repair was a month or more ago. Anyone care to have a guess or share thoughts? Martin, HS0ZED __ 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 donw...@embarqmail.com __ 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
[Elecraft] K3 died again
Hi, My K3 is quite an early unit, S/N 298. Recently upgraded with new synths KRX3A and KXV3, I also have a P3 connected to the radio. A while back it failed with a shorted smd capacitor on the K3REF board causing loss of TX bias voltage. Today it has lost both receive and transmit and I am thinking it might be from the same module. Here's the situation. Rig powers on and appears to work normally except soft noise from the speaker, no band noise to speak of and no signals. P3 shows plenty of signals, S9 plus on FT8 freqs but nothing heard other than soft noise. Tuning works as signals move in the band scope. No sub receiver signals either and no TX output. Have not checked transverter output but expect to find nothing there. P3 take off at IF output so everything is clearly working up to there. DSP seems to be working as width and shift cause the expected changes in audio. S meter reads dead zero, no movement. About the only common point I can see is the K3REF board so it would appear a second failure on this module. Since this is where I had to do earlier work I wouldn't put it past being a user inflicted fault, but that repair was a month or more ago. Anyone care to have a guess or share thoughts? Martin, HS0ZED __ 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
