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Did I fry my QMX SMPS or is it likely worse? #qmx

 

I accidentally fed 26v to my QMX. That's what I get for keeping too many running projects laying around, especially when they require wildly different voltages but the same plug format. Next time I'll tag the only correct supply.

Am I probably safe once the SMPS boards are replaced or is there a good chance for more damage?
 

Unplug the SMPS boards and check the resistance to ground of both the 3v3 and 5v0 supply rails on the main board. If the 3 volt rail shows only a few ohms or less there is a high probability that the MCU is toast.

JZ KJ4A?

On Tue, Feb 27, 2024, 3:38?PM K3KDW via <r.gammon=[email protected]> wrote:
I accidentally fed 26v to my QMX. That's what I get for keeping too many running projects laying around, especially when they require wildly different voltages but the same plug format. Next time I'll tag the only correct supply.

Am I probably safe once the SMPS boards are replaced or is there a good chance for more damage?

 

Thanks for the reply! Could you guide me on where to test?
 

K3KDW,

You want to measure the resistance on the bottom of the mainboard with the power supplies removed.? Attached is a PDF with the pin locations.

73
Evan
AC9TU
 

That pdf is gold. So I only have a few ohms between vcc and gnd and vdd and gnd. I don’t know what normal measurements are though. Is it worth ordering a fresh set of SMPS boards?
 

K3KDW,

No, I would not order the new boards.? I believe that you have damaged the 5 volt and 3.3 volt devices.? You could check with Jeff Moore W1NC on QRZ.com for his email address.? He can diagnose and repair the QMX and has had great reviews in this group.

73
Evan
AC9TU
 

Easy way is to check for short across the big yellow tantalum capacitor on each board. Test in both directions with a multimeter on a low ohms scale.? It should read open in at least one direction.? If it fails this test the zener diode is toast.


------ Original Message ------
From "K3KDW via groups.io" <r.gammon@...>
Date 2/27/2024 5:50:54 PM
Subject Re: [QRPLabs] Did I fry my QMX SMPS or is it likely worse? #qmx

Thanks for the reply! Could you guide me on where to test?
 

Hi Brad.?

I'm by no means an expert in this, but If you're reading single digits of resistance across the 2 rails on the main board to ground with the smps boards removed, then yes, your QMX has likely met its demise. I have a QMX on my bench (in the corner somewhere) that exhibits that condition, and after a quick exchange with Jeff Moore, who has repaired many these units, it became clear that the best way forward was to order a new QMX kit.

The good news is that that strategy has worked quite well for me, and I'm back on the air. ?

How frustrating your situation must be for you! So sorry!?

73

Roy - KI0ER?
 

Thanks for the help everyone. It was a fun build so when budget loosens up a bit I'll give it another go. Maybe by then the QMS will be out.

73 all
 

Sorry to hear that it’s dead.
No consolation, but it could be worse. I saw an ad a few weeks ago here in UK, for a week old Yaesu FTDX10 that the owner had given 55 Volts… Spares or repairs!

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