开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. QRPLabs
  2. Topics

QMX Heated Up, now no output

 

Using the same power supply (11.8v via BUC converter) and same antenna (Resonant 40m) that had been working for an hour, suddenly the unit quit putting out RF and when I put my hand on it it was very hot.
Disconnected power of course, and verified the SWR was still 1.3 on the 40m antenna.

This is an assembled unit from QRP-Labs.

I've done a reset via the menus, and let it cool overnight, no overheating now, but it's drawing slightly more current (0.12 increase to 0.24) at idle, and doesn't draw anything more at transmit.

I don't know where to start.
 

What type of BUC did you use? imho you are not the first, who's QMX died using a converter.
73, Wolfgang
 

Just an idea: Maybe there are power-supplies that don't like HF and change (increase) their output-voltage.
 

Depending on the quality and brand of power supply and what happens when it sees a load of RF coming back down its cable that's definitely a potential issue . .? ?

(50 years experience has taught me that good branded RF proof power supplies are a good use of money.? ?e.g. Pull the top of? a MeanWell professional market 'Mobile radio /base station power 13.6V supply and count the components not in the Chinese look-alike that's a quarter the size and 1/10th the cost)??

I'd fix the QMX, put the BUC supply on the naughty-shelf and see what happens with a decent supply and a well fitting plug . .?
 

开云体育

Tom,

Reheat T501. ?I had same problem. ?I don’t think that the QRP Labs scrapes any of the toroids wires and depends on the solder to dissolve the varnish. ?It took quite a while and higher soldering iron temperature until I was satisfied that the solder was adhering to the transformer wires. ?Everything is working fine now. ?It’s quite a fine rf tool at a reasonable price, even after paying them to build it.

Be the REASON someone smiles today.

Dave K8WPE

On Dec 26, 2024, at 7:20?AM, tom.rockhold via groups.io <tom.rockhold@...> wrote:

?
Using the same power supply (11.8v via BUC converter) and same antenna (Resonant 40m) that had been working for an hour, suddenly the unit quit putting out RF and when I put my hand on it it was very hot.
Disconnected power of course, and verified the SWR was still 1.3 on the 40m antenna.

This is an assembled unit from QRP-Labs.

I've done a reset via the menus, and let it cool overnight, no overheating now, but it's drawing slightly more current (0.12 increase to 0.24) at idle, and doesn't draw anything more at transmit.

I don't know where to start.
 

Regarding the QMX get the build instructions out, look through, understand and follow the schematic / circuit from 5351 to the PA transistors in 'transmit' to see if DC Voltage is getting to the PA transistors (Centre, top and bottom? Taps T501 primary)? and use a multimeter to see what is coming out of the driver IC' (IC502 and IC503) on transmit.? Will be an AC/RF signal but should read as a few volts of DC on transmit with a multimeter

1 - 6 of 6