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Kudos to Jeff W1NC

 

I sent my QMX to Jeff W1NC for repair but unfortunately I managed to blow the CPU because of lousy soldering.? He is very professional and quick so if you need any QRP Labs gear repaired give him a shout - I highly recommend him.

And because I am apparently a glutton for punishment I ordered another QMX kit hoping I learned enough lessons the first time.

73, Bill NZ0T?
 

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Ya know, blown CPU's seem to be very common on the QMX (mine was blown, too!)

Wonder why?

Paul -- AI7JR

On 9/27/23 07:01, nz0tham@... wrote:

I sent my QMX to Jeff W1NC for repair but unfortunately I managed to blow the CPU because of lousy soldering.? He is very professional and quick so if you need any QRP Labs gear repaired give him a shout - I highly recommend him.

And because I am apparently a glutton for punishment I ordered another QMX kit hoping I learned enough lessons the first time.

73, Bill NZ0T?

 

You can add my first QMX kit to the list of blown MPCs.? I believe that I caused the failure by testing out of the provided enclosure.? Pressing the encoders and buttons can flex the boards if not supported correctly.? My second one works as per specifications.? I am now cautious about supporting the boards when testing outside the enclosure.? I am looking into nylon standoffs to replace the screws that hold the mainboard to the display to see if that provides better board support.

The QMX is a very dense package with very little room for error.? It is GREAT if you want portability, not so if you do not need the small size.

Hans has put a lot of capability in a tiny package with several innovations that require new methods of construction and troubleshooting.? I believe that once learned, there is a much higher success rate.? Attention to detail and parts alignment are critical for this kit.? It's not one to be your first build.? I wish there were a "shack" or "+" version that would be about three to four times the size of the current QMX.? The QCX+ is a good example.

This is only 3 of over 1,000 kits sold, so it is not a high failure rate.? We are just the unlucky ones to be in the minority.
73
Evan
AC9TU
 

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I managed to destroy 2 MPU’s for my QCX. ?Both were entirely my fault but they don’t give you a 2nd chance. ?The slightest moment of short circuit or a little bit too high voltage and it is done for- instantly. ?You have to be extremely careful when handling them. Luckily replacements don’t cost much.

-Jerry, AC5JM?


On Sep 27, 2023, at 1:36 PM, Evan Hand <elhandjr@...> wrote:

?You can add my first QMX kit to the list of blown MPCs.? I believe that I caused the failure by testing out of the provided enclosure.? Pressing the encoders and buttons can flex the boards if not supported correctly.? My second one works as per specifications.? I am now cautious about supporting the boards when testing outside the enclosure.? I am looking into nylon standoffs to replace the screws that hold the mainboard to the display to see if that provides better board support.

The QMX is a very dense package with very little room for error.? It is GREAT if you want portability, not so if you do not need the small size.

Hans has put a lot of capability in a tiny package with several innovations that require new methods of construction and troubleshooting.? I believe that once learned, there is a much higher success rate.? Attention to detail and parts alignment are critical for this kit.? It's not one to be your first build.? I wish there were a "shack" or "+" version that would be about three to four times the size of the current QMX.? The QCX+ is a good example.

This is only 3 of over 1,000 kits sold, so it is not a high failure rate.? We are just the unlucky ones to be in the minority.
73
Evan
AC9TU

 

There have been a lot of discussions about protecting the BS170 power amplifier transistors from our bad SWR mistakes.? Zeners and TVS diodes get a lot of consideration.

BS170s cost about $.40 each and are very easy to replace.

The microprocessor is not easy to replace.? Fry it and you're back to Square One winding toroids for a new kit.? And probably grumbling even if you're a nice person.

So would overvoltage protection here be a good idea?? Even just on a temporary basis on a newly built board?? Maybe a nice burly 3V3 zener rated for 3 amps, to clamp VDD, at least until you know the transceiver works properly.? Here's an OnSemi part: 1N5913BRLG, under 50 cents at Mouser, qty 1.? It can dissipate 3 watts continuous.? It probably won't be happy at that, but you'll use your on-board test equipment (your educated finger) to see if it's happy.

Yes, I do see D109 on the 3V3 power supply board.? It's a 3.6 V zener but max dissipation is 1/2 watt.? I want a burly diode on my side during initial testing.? If your temporary zener even gets warm, you know there's a problem, but the MPU lives on to fight another day.

Look, I'm not a EE.? I can fix your brakes.? Is this a dumb idea?? Sanity check me, please.
GIUSEPPE
 

good morning everyone, my QMX also no longer works, I replaced the two power boards and it only turned on for a few seconds to be detected by the PC, then it turned off and never turned on again.? How can I understand if it should be thrown away, I checked every millimeter of the welds and everything is perfect.? I don't want to spend another �100 to buy another one.? Thank you and have a good day everyone .73

Giuseppe iu8eun

Il Gio 28 Set 2023, 01:43 Rich Brandt, AE8AA <richbrandt@...> ha scritto:
There have been a lot of discussions about protecting the BS170 power amplifier transistors from our bad SWR mistakes.? Zeners and TVS diodes get a lot of consideration.

BS170s cost about $.40 each and are very easy to replace.

The microprocessor is not easy to replace.? Fry it and you're back to Square One winding toroids for a new kit.? And probably grumbling even if you're a nice person.

So would overvoltage protection here be a good idea?? Even just on a temporary basis on a newly built board?? Maybe a nice burly 3V3 zener rated for 3 amps, to clamp VDD, at least until you know the transceiver works properly.? Here's an OnSemi part: 1N5913BRLG, under 50 cents at Mouser, qty 1.? It can dissipate 3 watts continuous.? It probably won't be happy at that, but you'll use your on-board test equipment (your educated finger) to see if it's happy.

Yes, I do see D109 on the 3V3 power supply board.? It's a 3.6 V zener but max dissipation is 1/2 watt.? I want a burly diode on my side during initial testing.? If your temporary zener even gets warm, you know there's a problem, but the MPU lives on to fight another day.

Look, I'm not a EE.? I can fix your brakes.? Is this a dumb idea?? Sanity check me, please.

 

Hi Giuseppe,

There is no sure way other than to try to isolate the problem.? If it is the MPU, the only choice is a new kit (you can save the cost of a new enclosure).? I did this by removing all the boards from the mainboard and measuring the resistance between the Vdd pin on the mainboard to 3.3 volt SMPS.? It was shorted.? This meant there was a short on the main board that was causing the problem.? I started to remove components from the mainboard that use the 3.3 volts, measuring the resistance each time until the MPU was left.? Since the short was still there, I gave up and assumed the main processor was toast relegating the kit to the parts bin.

73
Evan
AC9TU
GIUSEPPE
 

hi Evan, thank you very much, I looked for a short as you described and I didn't find it, only between Vdd and Gnd of the 3.3v card both with the card inserted and without the card it gives me a short, I don't know which Do.? And to think that the QMX was turned on for a short time.? I hope there is some other way to troubleshoot, unfortunately I don't have an oscilloscope for better troubleshooting.? I mean I'm going to throw it all away in the trash.? Thank you and good day

Giuseppe iu8eun

Il Gio 28 Set 2023, 07:22 Evan Hand <elhandjr@...> ha scritto:
Hi Giuseppe,

There is no sure way other than to try to isolate the problem.? If it is the MPU, the only choice is a new kit (you can save the cost of a new enclosure).? I did this by removing all the boards from the mainboard and measuring the resistance between the Vdd pin on the mainboard to 3.3 volt SMPS.? It was shorted.? This meant there was a short on the main board that was causing the problem.? I started to remove components from the mainboard that use the 3.3 volts, measuring the resistance each time until the MPU was left.? Since the short was still there, I gave up and assumed the main processor was toast relegating the kit to the parts bin.

73
Evan
AC9TU

GIUSEPPE
 

hi Evan, thank you very much, I looked for a short as you described and I didn't find it, only between Vdd and Gnd of the 3.3v card both with the card inserted and without the card it gives me a short, I don't know which Do.? And to think that the QMX was turned on for a short time.? I hope there is some other way to troubleshoot, unfortunately I don't have an oscilloscope for better troubleshooting.? I mean I'm going to throw it all away in the trash.? Thank you and good day

Giuseppe iu8eun

Il Gio 28 Set 2023, 13:30 GIUSEPPE via <iw8rsb=[email protected]> ha scritto:
hi Evan, thank you very much, I looked for a short as you described and I didn't find it, only between Vdd and Gnd of the 3.3v card both with the card inserted and without the card it gives me a short, I don't know which Do.? And to think that the QMX was turned on for a short time.? I hope there is some other way to troubleshoot, unfortunately I don't have an oscilloscope for better troubleshooting.? I mean I'm going to throw it all away in the trash.? Thank you and good day

Giuseppe iu8eun

Il Gio 28 Set 2023, 07:22 Evan Hand <elhandjr@...> ha scritto:
Hi Giuseppe,

There is no sure way other than to try to isolate the problem.? If it is the MPU, the only choice is a new kit (you can save the cost of a new enclosure).? I did this by removing all the boards from the mainboard and measuring the resistance between the Vdd pin on the mainboard to 3.3 volt SMPS.? It was shorted.? This meant there was a short on the main board that was causing the problem.? I started to remove components from the mainboard that use the 3.3 volts, measuring the resistance each time until the MPU was left.? Since the short was still there, I gave up and assumed the main processor was toast relegating the kit to the parts bin.

73
Evan
AC9TU

 

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DON'T DO THAT! Put it into your junk box, instead! If you ever build another, there are lots of salvageable parts that are useful.

Paul -- AI7JR

On 9/28/23 04:36, GIUSEPPE wrote:

hi Evan, thank you very much, I looked for a short as you described and I didn't find it, only between Vdd and Gnd of the 3.3v card both with the card inserted and without the card it gives me a short, I don't know which Do.? And to think that the QMX was turned on for a short time.? I hope there is some other way to troubleshoot, unfortunately I don't have an oscilloscope for better troubleshooting.? I mean I'm going to throw it all away in the trash.? Thank you and good day

Giuseppe iu8eun

Il Gio 28 Set 2023, 13:30 GIUSEPPE via <iw8rsb=[email protected]> ha scritto:
hi Evan, thank you very much, I looked for a short as you described and I didn't find it, only between Vdd and Gnd of the 3.3v card both with the card inserted and without the card it gives me a short, I don't know which Do.? And to think that the QMX was turned on for a short time.? I hope there is some other way to troubleshoot, unfortunately I don't have an oscilloscope for better troubleshooting.? I mean I'm going to throw it all away in the trash.? Thank you and good day

Giuseppe iu8eun

Il Gio 28 Set 2023, 07:22 Evan Hand <elhandjr@...> ha scritto:
Hi Giuseppe,

There is no sure way other than to try to isolate the problem.? If it is the MPU, the only choice is a new kit (you can save the cost of a new enclosure).? I did this by removing all the boards from the mainboard and measuring the resistance between the Vdd pin on the mainboard to 3.3 volt SMPS.? It was shorted.? This meant there was a short on the main board that was causing the problem.? I started to remove components from the mainboard that use the 3.3 volts, measuring the resistance each time until the MPU was left.? Since the short was still there, I gave up and assumed the main processor was toast relegating the kit to the parts bin.

73
Evan
AC9TU

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