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QDX - No transmit on 80M #qdx

 

Hi All,
I have a rev 3a QDX (80-20 model, firmware 1.10) that I built back around 10/2022. I used it more or less continuously for 6mo after building it, with great results. I wrapped T1 for 12v and usually ran it from my bench supply at 13.8-14.4v. I never had issues with heat - my shack is in the basement and is rarely over 60-65F, but perhaps this is the root of my problem?

In any case, I set it up again this morning and while going through the bands I discovered that 80M doesn't transmit at all. The LED pulses, but the meter on my ATU registers no output power. The rest of the bands seem fine - 5.5w on 20M, 7.3w on 30M, 5.9w on 40M, and 7.6w on 60M, tested using the built in transmitter tester. I see the same results using the tune button in WSJT-X.??

I shot a quick video here:


And have photos of the board here (I don't see anything wrong, but perhaps someone else will) -?



Any recommendations for things to check or test? I have a pretty standard complement of radio/lab gear to work with.

Thanks & 73s,
John K1QLN
 

John?

The usual culprit causing no output on one band is a bad solder joint at one or more toroid leads in the LPF for that band. That is usually? the result of inadequate enamel removal from the wire. It can be an intermittent problem. Check the solder joints and touch up if necessary.

JZ KJ4A?



On Fri, Feb 16, 2024, 10:10?AM John Miller via <k1qln=[email protected]> wrote:

Hi All,
I have a rev 3a QDX (80-20 model, firmware 1.10) that I built back around 10/2022. I used it more or less continuously for 6mo after building it, with great results. I wrapped T1 for 12v and usually ran it from my bench supply at 13.8-14.4v. I never had issues with heat - my shack is in the basement and is rarely over 60-65F, but perhaps this is the root of my problem?

In any case, I set it up again this morning and while going through the bands I discovered that 80M doesn't transmit at all. The LED pulses, but the meter on my ATU registers no output power. The rest of the bands seem fine - 5.5w on 20M, 7.3w on 30M, 5.9w on 40M, and 7.6w on 60M, tested using the built in transmitter tester. I see the same results using the tune button in WSJT-X.??

I shot a quick video here:


And have photos of the board here (I don't see anything wrong, but perhaps someone else will) -?



Any recommendations for things to check or test? I have a pretty standard complement of radio/lab gear to work with.

Thanks & 73s,
John K1QLN
 

That did the trick! I looked closely at the joints for L1 and L2 and noticed that one of L2's? pads (nearest IC3) wasn't fully flowed around the wire. It passed the continuity check when I assembled the board, but it must have been marginal. I reflowed it and the others on 80M just to be sure, and am now getting 7.1w on 80m.

Thank you!

John K1QLN
 

OK! Glad that worked!

A word of caution, though. Your power supply is pretty high for running a 12V QDX. You might want to bring it down a couple of volts, or perhaps two silicon diode drops in line.

73 JZ KJ4A?


On Fri, Feb 16, 2024, 11:05?AM John Miller via <k1qln=[email protected]> wrote:
That did the trick! I looked closely at the joints for L1 and L2 and noticed that one of L2's? pads (nearest IC3) wasn't fully flowed around the wire. It passed the continuity check when I assembled the board, but it must have been marginal. I reflowed it and the others on 80M just to be sure, and am now getting 7.1w on 80m.

Thank you!

John K1QLN

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