开云体育

Bit of a background powered up after the QMX loaded the FW.
Then a few hours later radio died.? ?What I've found is there is a direct short on the main pc board for the VDD bus.? This is present with both the smps? boards removed.
Short is between pins 4 and 6 of the angled header for the 3.3-volt bus board.? I've looked very carefully for any solder bridges etc. Ohm meter reads 0.6 of a ohm.
between pins 4 and 6.? And yes, I did a lot of searching on this forum, but I could have missed something.

Any leads or ideas would be greatly appreciated.??

Thanks, and 73

Ray? VE7AVG/VA7SK

Hi Ray,

These symptoms happened to my QMX after I tried to repair an issue with the volume encoder.? The process that I followed was to try to isolate the short by removing components.? With all the plugin boards removed, I first removed L201 and L202.? I still had the short.? Then I went on to IC501 and IC502.? The short was still there.? The last one I removed was IC201, and the short remained.? At that point, I determined that the discrete components were not likely to have failed.? The major IC left was the processor, with no easy way to isolate it.? I gave up at that point and figured the processor was bad.? There is no way I could remove and replace that IC with my tools.? I will start with a fresh kit (I bought two for this type of issue) and try again.

I should mention that I tested the 3.3-volt regulator board and, without a way to energize it, determined that all static measures were as expected.? I do not know if it could have caused the failure with a power surge, but the Zener seemed intact.? This should rule out a power surge through the converter.

The encoder board has several I/O pins that directly connect to the processor.? When I tried to repair it, there may have been a short from a 12-volt line to one of those pins (the processor I/O is 5-volt tolerant).? I wonder if the short could have happened to your board as well.

When I get home from a family trip, I will look closely at the QMX to see If there is a possible short with a miss-aligned control board.

I hope that your experience is better.
73
Evan
AC9TU

Hi Evan,
Thanks for the reply.?
I made a point of reading the assembly manual and noted there was a section that mentions some components are sensitive to static electricity.? ?So, with this in mind used static protection ie strap, mat and grounded soldering irons.
As mentioned after loading the software was able to transmit with it, dummy load, and was getting around 4 watts out on 30 meters.? So, all seemed well. After a short time, 5 minutes, the display went dark. During the 5 minutes the radio was in receive mode. Would not reboot.? So checked for shorted components on the smaller smps board.? One of the diodes with W4 written on it showed it was shorted.? Pull the board out no short.? So measured resistance across the 6-pin right angle header and found two on the bottom row center and right side were shorted.? Measured across C214 near the?STM32 chip, measured a short.? That is as far as I can go as I don't really have the ability to do board level repairs.
This would have been the 11th QRP labs kit over the years.? Guess it's not to be.
73
Ray VE7AVG?

I’ve seen this a number of times on several QMX rigs that I’ve worked on. ?In my experience it has always been a short inside an IC. ?Most often it has been the cpu. ?I’ve also seen a Capacitor on the VDD rail blow up and short. ?My belief is that it happens when some voltage that is too high (5v or 12v) gets put out on one of the pins of the cpu or onto the VDD rail itself. ?Why this happens is less clear. ?My guesses are: a microscopic wire or solder bridge creates a short, a mechanical event (like pressing a button) causes a short, a meter or scope probe accidentally bridges 2 pins. ?I’ve seen evidence of all these on different rigs.

I usually find the short with a milliohm meter, and by lifting power pins from ICs or by removing caps to confirm. ?It’s rather tedious but often leads to the dead IC. ?

73
Jeff
W1NC

Hi Jeff,

Do you mean capacitor C433?? has the value.? C106 written on it.? Radio died after 5 minutes in receive mode.

Thanks

Ray VE7AVG

I don’t remember which cap failed in the past. ?There are several connected to VDD. ?Most likely is an IC. ?I can look at it for you if you wish. ?I’m in QRZ for an address.