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High SWR -- QMX+

 

Hi Radio Friends.
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Unfortunately, I have a QMX+ with high SWR and I don't quite have the electronics knowledge to diagnose much deeper without a little help. This isnt quite my day job, but trying to learn the best that I can.
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I own an oscilloscope and signal generator in case those would help in troubleshooting.?
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As a note, I have accidentally broke L520 while winding it, so for the time being I just ran a jumper between those two pads. Because of this, I havent included the 6m band in any of my screenshots.?
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Would any of the attached screenshots help shed light on what could be the issue? Ive taken a screen shot of every diagnostic tool for all bands except 6m
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Thanks ahead of time for any and all help. Im also building a second QMX+, so might have to check in with that one as well once I am done building it.?
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Regards,
Chris
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Hi Chris
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We need more info
High SWR into a dummy load or into an antenna
What bands
What type antenna
Do you use an antenna tuner
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72 73
John
N3AAZ
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Hi Chris,
Sorry if this was obvious but you need to connect a good load to the antenna socket to run the diagnostics. It looks like your running with nothing connnected? else you have a problem with the bridge T507 and the associated circuit D514/D515 ... Most likely T507 as its easy to cross connect.
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--
G0TXL (Paul)
 

Do you have a licence to operate this equipment ?
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Is the jumper installed between the two center pads of JP501?
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Al, K2ZN
 

Thank you all for the feedback.?

-Into a dummy load
-SWR seems to get incrementally worse from 10m, and then it falls off bad?
- Haven¡¯t got it running good enough to use with antenna
-Jumper installed at JP501
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I¡¯ll take a closer look at T507 and D514/D515 today, check the BNC for shorts and report back
 

Just a quick comment.

The BNC WILL show as shorted with a multimeter since the meter is DC.?

( I learned that after cutting one of mine out before even first powering up. Jury rigged a BNCish dongle while waiting for an exact replacement from Turkey.? DOH! )

GREG KI4NVX?



On Thu, Oct 17, 2024 at 10:26 AM, Chris - 7 Land
<christopher.j.richins@...> wrote:
Thank you all for the feedback.?

-Into a dummy load
-SWR seems to get incrementally worse from 10m, and then it falls off bad?
- Haven¡¯t got it running good enough to use with antenna
-Jumper installed at JP501
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I¡¯ll take a closer look at T507 and D514/D515 today, check the BNC for shorts and report back
 

Chris,
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For what it is worth, I've put images of my QRP labs experiments under photos in this groups.io. Jumper JP501 also tricked my once. Also the jumpers below the GPS receiver are tricky, and I nearly killed the LCD display and push buttons by soldering them on the wrong side. In the end everything does work.?
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73 PA1EJO Ernst
 

On the QMX there is the T507 transformer which is I believe for SWR, not sure if it's the same on the QMX+ but I would check the solder joints on those and test continuity.?
 

indeed, follow the PCB wiring and check the continuity there, this is how I found the JP501 problem
 

Update!
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I¡¯m extremely thankful for the fast assistance to help me hone in on the issue. Hit the T507 with a strong dose of heat and I believe I may have resolved it!

I think I was so caught up in making sure the LPFs had continuity that I failed to check T507.
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Going to check again after work.
 

For completeness, here are some diagnostics of before and after reheating the joints on T507 for the 40m band. Similar performance obviously occurred on all other bands.
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BEFORE
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AFTER
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Diagnostics After the repair:
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Thanks all!
73 de Chris

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