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qcx 20 metri burned transistors
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Hello
tonight I went to turn on my 20-meter qcx and it did not work
a faint smell of burning in the air of the three mosfet q3 was burned, one could see by eye.
not knowing how to measure them I took all three from the circuit.
even with these transistors removed, however, nothing is received and the voltage regulator is very hot.
I also found tr 6 shorted once removed, as it is difficult to work with double-sided circuits, the controller returns to normal temperature but still does not work.
I would like to replace the 4 transistors but I do not know if I find them on the market and it is possible that there are still faulty components?
what should I do?
I'm waiting for your answer
thanks for everything 73 and happy new year !!
ik5lwe luciano tarli Prato |
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Jess Gypin
I am currently working on exactly the same problem. First power up Q2 got super hot. Q6 was shorted. Replaced Q6 and all 3 PA transistors. Second time all was well. Did the alignment and IQ balance and others showed very little peaking. Band pass cap adjusted well to the half way point. Receiver sounded good. On first attempt to transmit, no power out at all. Got side tone and receiver muted. From that point on, PA transistors getting hot again. At this point I have changed all of the 170 transistors and Q6 again. Receiver is working, still no apparent peaks in alignment, band pass cap adjustment is good. I have not tried transmit as I want to check the circuit as operational as possible. I suspect that the sig gen line and the transmit line going to the nand gate or something after that may have them both in at the same time causing the PA to be in when it should be off or clocked by the oscillator. I have not found the problem but that have been a couple of other posts that have indicated a similar problem. Jess AE0CW On January 4, 2018, at 8:03 AM, luciano tarli <ik5lwe@...> wrote: Hello
tonight I went to turn on my 20-meter qcx and it did not work
a faint smell of burning in the air of the three mosfet q3 was burned, one could see by eye.
not knowing how to measure them I took all three from the circuit.
even with these transistors removed, however, nothing is received and the voltage regulator is very hot.
I also found tr 6 shorted once removed, as it is difficult to work with double-sided circuits, the controller returns to normal temperature but still does not work.
I would like to replace the 4 transistors but I do not know if I find them on the market and it is possible that there are still faulty components?
what should I do?
I'm waiting for your answer
thanks for everything 73 and happy new year !!
ik5lwe luciano tarli Prato |
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did this happen on power up, with pressing a key or keyer?? first, insure you don't have a short circuit making the QCX stay in transmit.?
my QCX experienced plenty of smoke - but I sense my BS170 devices likely were not damaged (I replaced them unnecessarily).? the PNP transistor feeding them is more likely to be damaged (mine still worked by constrained output power to 1.8 watts - replacing it I have 3 watts again).? I suggest inspection to rule out simple problems before replacing anything.? put a load on the antenna port while troubleshooting - a 5 watt dummy load is not hard to make.? then check to see if the unit is transmitting at power up.? if all is well, then I would consider replacing only the PNP transistor - for CW operation any common type than can handle at least 600 mA should work.? the hot regulator deserves a look, and I don't know if it is related.? it can only be hot with a short somewhere, and doesn't feed the PA parts as I remember.? proceed with care - most of us that have built things are experienced these things.? I hope its a simple fix when you find it, avoid actions that damage the unit (unnecessary replacement, being stuck in trasmit with no antenna load).? Curt |
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Steve Nichols
I have just been through this with my 20m QCX.? Turns out IC3 had failed (probably after the 5V regulator failed). Even after I replaced the regulator and IC3 (I used a socket this time) it still didn't work. But I noticed that Q1 was hot even on receive.? Replacing this (again) brought the TX back to life.
It is worth checking that you don't have short from the centre pin to earth. And also that you have continuity from the antenna to C29 to show the LPF is not open circuit. I would check the voltages on the pins of IC3 - I listed mine (key up and key down) in another thread. When my IC3 failed I still had receive audio but at much reduced volume, although the sidetone was still normal. Hot Q1, Q2 or Q3 on receive might indicate failure. Steve G0KYA |