Re: QCX 40 Up in smoke !

Vernon Matheson

Paul I have run mine on 40m WSPR for days and days and no issues…supply was 13.8 volts…even the voltage regulator did not get that warm.




From: [] On Behalf Of K2DB Paul Mackanos
Sent: Monday, July 15, 2019 7:42 PM
Subject: Re: [QRPLabs] QCX 40 Up in smoke !


 Thinking about this further, the day before it went up in smoke I came in the back door and thought that I smelled a slight Electronics burning smell. I walked all around the house and couldn't find it. It was the next day that I got on and started to call CQ when it went up in smoke. Here is what I think happened, from the day I got it working and all aligned, I had never turned it off, I had it installed in the qrp labs CW transceiver box I bought from Germany. My thought is that the heat eventually built up over that time and when I stressed it by hitting the key, that's when the parts went kabang. I'm thinking about buying a miniature little 5 or 12v fan, cutting a little hole in the back where the output transistors are, and cooling it down. I would think that the way it was designed and with the enclosure, that that would have all been taken into account. But, I've been wrong before it may have just been a faulty part or something, I just got the replacement transistors from digikey and tomorrow I will try and fix it. I guess another thing I could do is not leave the power on it 24/7.

73 Paul K2DB


On Fri, Jul 12, 2019, 12:18 AM Dan Pflugrath <dpflugrath@...> wrote:

In my case I was getting about 3.5 watts output (QCX Ver 3 after removing 2 turns from L3 and replacing the output filter capacitors with micas.) and turned up the power supply to 16 volts to see what the output power would do.  I found Q2 (BS170) shorted and Q6 (MPS2907) blown open because of the shorted Q2.  To bring it back to like new I replaced Q1, Q2, Q3, Q4, Q6 and IC3.  I thought IC3 could have been damaged because of how Q2 was shorted.  It is now working well and for some reason I am now getting just over 5 watts output.  The QCX is now performing well and running on 13.5 volts only!

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