Dead K2 After nearby power surge
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I also just noticed that the power output transistors Q7 and Q8 are getting warm when the power is on. I did not say before but, their is no display or any other activity on the control board or front panel.
Fred, KC9QQ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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I also just notice that the transistors Q7 and Q8 are getting warm when the unit is powered. Even though the display is dead. Fred |
Re: Dead K2 After nearby power surge
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In reply to this post by KC9QQ
Fred,
In cases like yours, first step is to connect a dummy load to the K2 just in case it is trying to transmit - it is not good to enter transmit state without a load on the PA transistors. If it is a K2/100, remove the KPA100 and connect the dummy load to the BNC antenna jack on the lower rear panel. First thing is to check the state of the 8T and 8R voltage rails. Those are easily checked at the anodes of D6 and D7. If D7 anode has 8 volts on it while D6 anode has zero volts, then the K2 is in a transmit state. If both D7 and D6 anodes have 8 volts present, power it only briefly while making further checks lest some components overheat. If both 8T and 8R are present, you need to check the state of the RX signal at the gate of control board Q4 as well as the TX signal at the gate of CB Q3 - one should be on (about 5 volts) while the other should be off (near zero volts). If both of these are on, the microprocessor was zapped with the power surge, but if only one is on, the problem is a shorted Q3 or Q4 on the control board. 73, Don W3FPR Fred Keller wrote: > I also just noticed that the power output transistors Q7 and Q8 are > getting warm when the power is on. I did not say before but, their > is no display or any other activity on the control board or front panel. > > Fred, KC9QQ > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by KC9QQ
I also pulled the control board and re-powered the unit with the control board removed. I heard relays click on the RF board. I then re-installed the control board and re-powered the unit. The display came on for just a few seconds with the Elecraft name and then went blank probably after the 12V pulled down. I am not quite sure where to look to further isolate the issue. I know the unit was on the 40 M band when the problem occurred. Fred |
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In reply to this post by Don Wilhelm-4
Don, I pulled the control board again to reset the relays and then reinstalled it to make the measurements on D6 and D7. When I powered the unit, Elecraft was again shown and the frequency of 7100 was briefly displayed. When then display went out I measured the anodes and cathodes of both d6 and d7 and measured nearly zero volts on both. Fred |
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I tested the voltages on D6 and D7 anodes again when I powered up. I had to power up twice, but each showed around 7 volts before they fell to near zero. I have found that I can let the unit sit for a few minutes before I re-power and I don't have to pull the control board to reset the relays. This only gives me about 2 seconds to make the measurement. The voltage on the gate of Q4 is 5 volts. The voltage on the Gate of Q3 is close to zero for the brief period I have to make the measurement. After a few moments the gate of Q4 drops to zero. How do I tell which is shorted? I made the following measurements to resistance measurements referenced to ground. Q3 S - 0.4 M G - 5.4 M D - 8.1 M Q4 S - 0.3 ohms G - 3.9 K ohms D - 8.1 K ohms I am assuming the culprit is Q4. Am I correct? Is it possible the something else is fried that may take out Q4 if I install a replacement? I still have 4 boards that I have not built (SSB, DSP2, AT and NB). I believe at least one of these has a 2N7000 I can rob for a temporary replacement. I just don't want to install it until I am sure another failure somewhere else upstream won't cause it to fail. Are there any other items I should check before I replace the failed transistor? Thanks, Fred Fred Fred |
Re: Dead K2 After nearby power surge
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In reply to this post by KC9QQ
Fred,
Zero volts on both is way better than 8 volts on both - at least the K2 is not trying to transmit. Check the gates of Q3 and Q4 on the control board. The gate of Q4 should be at 5 volts and the gate of Q3 should be near zero. If that is true (and only if that is true), short the drain of Q4 to its source and see if the 8R voltage rail comes to life - 8 volts at the anode of D6. If so, replace Q4. If still no 8 volts on 8R, then something is wrong with Q2 (likely open). OTOH, if the gates of both Q3 and Q4 are near zero volts, you have a bad microprocessor output. 73, Don W3FPR PS: Top posting is preferred here, it is easier to see the latest without scrolling all the way to the bottom - on some posts it is hard to determine what has been added - I know about 'netiquette', but that is slow and laborious. KC9QQ wrote: > > Don Wilhelm-4 wrote: > >> Fred, >> >> In cases like yours, first step is to connect a dummy load to the K2 >> just in case it is trying to transmit - it is not good to enter transmit >> state without a load on the PA transistors. If it is a K2/100, remove >> the KPA100 and connect the dummy load to the BNC antenna jack on the >> lower rear panel. >> >> First thing is to check the state of the 8T and 8R voltage rails. Those >> are easily checked at the anodes of D6 and D7. If D7 anode has 8 volts >> on it while D6 anode has zero volts, then the K2 is in a transmit >> state. If both D7 and D6 anodes have 8 volts present, power it only >> briefly while making further checks lest some components overheat. >> >> If both 8T and 8R are present, you need to check the state of the RX >> signal at the gate of control board Q4 as well as the TX signal at the >> gate of CB Q3 - one should be on (about 5 volts) while the other should >> be off (near zero volts). If both of these are on, the microprocessor >> was zapped with the power surge, but if only one is on, the problem is a >> shorted Q3 or Q4 on the control board. >> >> 73, >> Don W3FPR >> >> Fred Keller wrote: >> >>> I also just noticed that the power output transistors Q7 and Q8 are >>> getting warm when the power is on. I did not say before but, their >>> is no display or any other activity on the control board or front panel. >>> >>> Fred, KC9QQ >>> >>> > Don, > > I pulled the control board again to reset the relays and then reinstalled it > to make the measurements on D6 and D7. When I powered the unit, Elecraft > was again shown and the frequency of 7100 was briefly displayed. When then > display went out I measured the anodes and cathodes of both d6 and d7 and > measured nearly zero volts on both. > > Fred > > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: Dead K2 After nearby power surge
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In reply to this post by KC9QQ
Fred,
We are 'doubling' with overlapping posts here along with fast paced responses. From that brief measurement, I think Q3 is the problem - I base that on the fact that you measure 8 volts on both D6 and D7. Just remove Q3 to check that theory. The K2 will receive without Q3 installed, but will get mixed up if you try to transmit. If you get receive and a display with Q3 removed, then a new 2N7000 should fix it. BTW, you cannot check a transistor or FET for short/open by making resistance measurements - it is just not reliable nor predictable. 73, Don W3FPR KC9QQ wrote: > > KC9QQ wrote: > >> >> Don Wilhelm-4 wrote: >> >>> Fred, >>> >>> In cases like yours, first step is to connect a dummy load to the K2 >>> just in case it is trying to transmit - it is not good to enter transmit >>> state without a load on the PA transistors. If it is a K2/100, remove >>> the KPA100 and connect the dummy load to the BNC antenna jack on the >>> lower rear panel. >>> >>> First thing is to check the state of the 8T and 8R voltage rails. Those >>> are easily checked at the anodes of D6 and D7. If D7 anode has 8 volts >>> on it while D6 anode has zero volts, then the K2 is in a transmit >>> state. If both D7 and D6 anodes have 8 volts present, power it only >>> briefly while making further checks lest some components overheat. >>> >>> If both 8T and 8R are present, you need to check the state of the RX >>> signal at the gate of control board Q4 as well as the TX signal at the >>> gate of CB Q3 - one should be on (about 5 volts) while the other should >>> be off (near zero volts). If both of these are on, the microprocessor >>> was zapped with the power surge, but if only one is on, the problem is a >>> shorted Q3 or Q4 on the control board. >>> >>> 73, >>> Don W3FPR >>> >>> >>> >>> >>> >> Don, >> >> I pulled the control board again to reset the relays and then reinstalled >> it to make the measurements on D6 and D7. When I powered the unit, >> Elecraft was again shown and the frequency of 7100 was briefly displayed. >> When then display went out I measured the anodes and cathodes of both d6 >> and d7 and measured nearly zero volts on both. >> >> > > I tested the voltages on D6 and D7 anodes again when I powered up. I had to > power up twice, but each showed around 7 volts before they fell to near > zero. I have found that I can let the unit sit for a few minutes before I > re-power and I don't have to pull the control board to reset the relays. > This only gives me about 2 seconds to make the measurement. > The voltage on the gate of Q4 is 5 volts. The voltage on the Gate of Q3 is > close to zero for the brief period I have to make the measurement. After a > few moments the gate of Q4 drops to zero. > > How do I tell which is shorted? I made the following measurements to > resistance measurements referenced to ground. > > Q3 > S - 0.4 M > G - 5.4 M > D - 8.1 M > > Q4 > S - 0.3 ohms > G - 3.9 K ohms > D - 8.1 K ohms > > I am assuming the culprit is Q4. Am I correct? Is it possible the > something else is fried that may take out Q4 if I install a replacement? I > still have 4 boards that I have not built (SSB, DSP2, AT and NB). I > believe at least one of these has a 2N7000 I can rob for a temporary > replacement. I just don't want to install it until I am sure another > failure somewhere else upstream won't cause it to fail. Are there any other > items I should check before I replace the failed transistor? > > Thanks, > > Fred > > > > Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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