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Hello,?

'fraid my QDX let out the magic smoke today.?

I had one of these rare moments when it would not transmit after changing band / frequency. I unplugged from both PC and power, plugged pwer back in and it started smoking and stinking immediately. Two leftmost BS17o get very hot and smoke.?
12V build, latest Firmware 1_10, being run at 11,3V - first thing I checked was if my downconvertar had gone nuts - no, it hasn't, it's outputting wonderful 11,3V, under load and without.?

Should changing the 4 BS170 (I have been so cautionary to stock some) fix the issue or should I look at something else before, lest I burn them again straight away??

73 de EA7KLK, Volker

Ah, yes. more data. This happened on 40m, 7074 KHz. I was transmitting sucessfully right before, couple of POTA QSOs, tuned antenna to SWR 1,2:1 (with NanoVNA)?

73 de EA7KLK Volker

On 28/02/2024 17:54, Volker Kerkhoff wrote:

Should changing the 4 BS170 (I have been so cautionary to stock some) fix the issue or should I look at something else before, lest I burn them again straight away?

Volker,

Remove the BS170s.
Test for 5 volts at the gate pads when in transmit. 0 volts receive.

If good replace BS170s.
Maybe consider a diode across L14, could protect against one failure mode.

73 Alan G4ZFQ

Measured, all good, replaced BS170s and back in business, 5 quick QSOs over Europe from my balcony on the 1st floor are proof

Congrats on successful surgery! I second the suggestion to add an L14 diode to protect against a possible failure mode that sounds consistent with what you described. Other than the L14 voltage, I have also observed low efficiency and resulting thermal dissipation issues for my hi-band QDX only on 10m; 20-12m are fine. So you could also check whether the efficiency looks okay across all bands for you.