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What Mods to Early Rev 1 QCX Mini

 

Hi, I have an unbuilt Rev 1 QCX Mini (circa 2020) that I want to start, but I remember that there was some kind of a problem with, I believe, the power supply circuit.? Where will I find the documentation for a Rev 1 build and necessary modifications?

Thanks in advance,
73, Greg, KM5GT
 

It¡¯s on the QCX Mini page on QRPLabs website. Use instructions for Rev1&2 but not the addenda for Rev2. The instructions to add a 10 uf tantulum or electrolytic capacitor to the voltage regulator are in the document. Be careful to never short the 5v rail to ground. Doing so will cause this regulator to fail shorted and it will put 12 volts on the 5 volt rail and destroy all the 5v components. There is a workaround to replace the 5v regulator with a 78M05 that doesn¡¯t have this issue.?

Good luck. ¡­73¡­ Ron

On Tue, Mar 12, 2024 at 14:15 Greg Tilford <GregTilford@...> wrote:
Hi, I have an unbuilt Rev 1 QCX Mini (circa 2020) that I want to start, but I remember that there was some kind of a problem with, I believe, the power supply circuit.? Where will I find the documentation for a Rev 1 build and necessary modifications?

Thanks in advance,
73, Greg, KM5GT

 

Hi Greg,

I bought an unbuilt kit of the same vintage recently.
It requires a capacitor on the power input to prevent potential damage from supply spiking.
D33 cathode to 0V.
10uF tantalum or electrolytic.
Described and shown in QCX-mini assembly Rev1.05. Pages 67 - 69.

If you¡¯re installing AGC module there are a couple of wires to be added, information in AGC manual.

73.
 

Tnx all.? Not that I *plan* on shorting the 5VDC to ground, but replacing the regulator with a 78M05 is appealing.? Where will I find details on that fix?? Is it drop-in, or does it require some creative wiring?

73, Greg, KM5GT
 

It's an easy mod. You just move the 7805 over to the left one pin and solder the left most pin to the bottom of the diode.?

--
73, Dan - W2DLC
 

Dan, Rowan and Ron, thanks for your help.? I think I am off and running.

73, Greg, KM5GT
 

Greg,? I think I also trimmed most of the tab off so it wouldn't interfere with other components.?
--
73, Dan - W2DLC
 

Thanks for all the pointers.? I went ahead and added the tantalum capacitor.? More filtering is always good, right?? Also, for some reason my regulator had the center pin clipped.? Since the heatsink tab on the QCX isn't connected to the ground plane I had to create a makeshift extension to the center pin.? Otherwise, all went smoothly, and the radio is operating well.? Now all I have to do is learn CW, lol.?

73, Greg, KM5GT

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