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QMX 60-15 Build -- No Transmit on 60m and 40m. But Wait, There's More !

 

After what I thought was a particularly careful build, the QMX 60-15, 12 volt radio failed to produce RF output on 60 meters and 40 meters.? All other bands were optimal.

I immediately suspected L506 and L511, which handle LPF duties for both 60 meters and 40 meters. I reheated the joints to no effect.

Then I did a meticulous search all over the board for any obvious solder bridges, and along the way reheated joints that looked remotely suspect.? No luck.

I did a few Firmware Updates and Factory Resets.? No change. 60 and 40 were still mute.? I could hear the CW sidetone, but zero output. Other bands output was fine.??

But then.

Lacking other options, I decided to fiddle in the software.? When I changed the band plan in System Config to 160m-6m -- I got just over 5 watts output on 40 meters !? ?But (sigh) all other bands were lacking any RF output.

I then changed the System Config to 80-20 -- and got just over 5 watts RF output on the 40 meter, 30 meter and 20 meter bands !? No output on the others.?

I concede I may have missed a hardware fault of mine or the radio's, but what I'd really like is a normally functioning mid-bands QMX.

Thoughts on what's going on here, and how I might resolve it would be greatly appreciated.

Many thanks,

Bill? ?W3WJ
 

Hi Bill. You should look at voltages on diodes D508 and D511. The cathodes of those diodes should be at some voltage like 5 volts when not selected and at close to zero volts when selected. If tht's?not the case, check enamel removal again on L506 and L511. Also check continuity through L505 and make sure the drain of Q506 is going down to near zero volts when that filter is selected.
Hope that helps ... Ron

On Sun, Jun 23, 2024 at 5:03?AM Bill Jobes via <jobes=[email protected]> wrote:
After what I thought was a particularly careful build, the QMX 60-15, 12 volt radio failed to produce RF output on 60 meters and 40 meters.? All other bands were optimal.

I immediately suspected L506 and L511, which handle LPF duties for both 60 meters and 40 meters. I reheated the joints to no effect.

Then I did a meticulous search all over the board for any obvious solder bridges, and along the way reheated joints that looked remotely suspect.? No luck.

I did a few Firmware Updates and Factory Resets.? No change. 60 and 40 were still mute.? I could hear the CW sidetone, but zero output. Other bands output was fine.??

But then.

Lacking other options, I decided to fiddle in the software.? When I changed the band plan in System Config to 160m-6m -- I got just over 5 watts output on 40 meters !? ?But (sigh) all other bands were lacking any RF output.

I then changed the System Config to 80-20 -- and got just over 5 watts RF output on the 40 meter, 30 meter and 20 meter bands !? No output on the others.?

I concede I may have missed a hardware fault of mine or the radio's, but what I'd really like is a normally functioning mid-bands QMX.

Thoughts on what's going on here, and how I might resolve it would be greatly appreciated.

Many thanks,

Bill? ?W3WJ

 

On Sun, Jun 23, 2024 at 02:03 PM, Bill Jobes wrote:
When I changed the band plan in System Config
Hello Bill, doing so is dangerous for the PA. The PA is working towards the wrong LPF regarding the used frequency.

Like you I think something related to LPF0 is wrong. There could be more wrong but the coils. Please read this page from the QRP Labs Wiki for debugging.

73, Ludwig
 

Sorry Ron, we wrote at the same time.
 

Thanks for the caution warning, Ludwig. I returned it to the 60-15 config and to its case after some more unproductive fiddling. I'll just life without 60 and 40 on the radio for now.?
- Bill W3WJ??
 

Thanks, Ron for the suggestions.? I thought I'd scraped enough enamel off originally; perhaps not. I put it back in its case for now and will give it another look this week.

- Bill? W3WJ
 

SUCCESS !

After trying once again to reheat the joints, this time with an iron temp of 860F and long holds on the sites,? I resolved the issue.? Must have been enamel.?

RF Output are now enabled on 60 and 40 meters, where the radio was dead before.

Here are the output results, powering the 12-volt build with 11 volts.

60M? 7.8
40M? 5.8
30M? 5.2
20M? 5.4
17M? 5.3
15M? 3.0

Thanks to all for the suggestions.??
73,
Bill? W3WJ

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