Well... I just finished my second QMX, the first one was toasted by increasing the supply voltage from 6V to 12V wiith a ramp-up time of 3milliseconds.
The full story is here:?/g/QRPLabs/message/106237

That one was? running firmware 1.07. Image. D109 was destroyed (short) so I removed it.
After that my QMX turned on but power? consumption was200mA @12V input.
Image rejection was nonexistant and bandpass filters totally wrong, so I concluded IC402 and/or IC403 were damaged.
I decided to stop there and ordered a new kit

Now the second QMX, finished last night:
I loaded firmware 1.09 without problems.
Everything was fine and I was just about to write something on the forum of a successful build.
I wanted to put in some figures of RF power output and current consumption.
Power output was fine 4W on all bands @12V supply. Image rejection and filter sweeps were also fine. Supply current about 100mA in receive and 600mA in transmit
But while I was measureing supply current I heard a "crack" and the QMX turned itself off.
I turned it on again by pressing the left rotary switch.
Now I smelled burnt electronics.
I opened the case and out came the holy smoke...
C107 was now black and with a large crack in it.
I took out the power board and removed C107 and measured the resistance between Vcc and GND.
733 Ohms in both directions with the DMM, so i removed D108. Now I had 75 kOhm in one diection and about 7 kOhm in the other.
I also checked Q108, no short between terminals, so I guess it survived.

So I took the 5V power board from my first QMX and put it into the second.
And voila, everything back to normal.

So what happened?
During the current measurement It is possible that I interrupted the power supply line shortly when I disconnected the DMM without powering down the QMX before.
But htis case was addressed by Hans in his article about SMPS behaviour during input voltage step...

There is a saying in swedish "en g?ng ?r ingen g?ng, tv? g?nger ?r en gong-gong"
Free translation: One time is OK, two times is an alarm clock.
I can see that several QMXs have blown up C107.
I think this is no coincidence. There is something going on here
I recall that all who reported blown C107 were running 12V supplies with high current capability

I suspect a HW/SW interaction:
During a power interruption glitch, is it possible that the processor can leave the the PWM signal high, thus creating a voltage increase that kills C107 and D108?
I would suggest that the PWM-signals should be AC-coupled so that if stuck high, the SMPS would turn itself off.

73 de SM5EIE /Gunnar
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So I ordered?

On 25/08/2023 11:03, Chris wrote:

That's so dead that it seems to be more than T401 soldering,

Chris,

But if the wires are in the wrong holes reception could be zero.

73 Alan G4ZFQ

On 25/08/2023 20:09, W GALAUGHER wrote:

L4 started smoking. Yikes!
Now terminal shows only 80m, no other bands. Wsjt works into 50 ohms but usb sketchy
Replaced L4. Removed Diodes D1 and D4, they were shorted.
Where to next?

Maybe a better description.
What version QDX?
L4?? are you sure?
Terminal shows only 80m, do a reset?
WSJT works? RX and TX? All bands?
USB sketchy? How?
D1, 4 shorted? Seems unlikely.

73 Alan G4ZFQ

On 25/08/2023 12:53, KB9NBL wrote:

but no or limited reception

James

Q6 failure has been reported, possibly static from antenna.
Or, a bad joint showing up.

73 Alan G4ZFQ

On Thu, Aug 24, 2023 at 08:51 PM, Gary W9TD wrote:

The Microham USB interface III driver/configuration program works fine on my W10 machine.

I downloaded the new driver and virtual port installer yesterday.
I tried it on my laptop (Win10) and desktop (Win11) and all worked as expected, but haven't connected a radio yet.
The cables I have were for some radios I no longer have.? I'll have to make some new ones.

I am glad someone asked the question.? It made me look at a piece of equipment that I wasn't using - but could be!
-------
Rob KB8RCO

The voltage on LIN_REG_EN is a little over 0.7 volts when the power on switch is pressed, which leaves me a bit suspicious... Still don't understand what could've compromised the CPU.

开云体育

Well, I thought I had an easy glide path. Repairing the Q103/Q104 short, I damaged (lost) R104 and D102. Turns out what I was seeing was, with no pull up, once connected to the supply the 12 volt supply drifted upwards until the unit turned itself on!

Repaired the board with discrete components and tried powering up again.

No Joy. :-( Looks like the repaired board is doing what it should, but the 3.3 volt supply (which had to be working before!) is not coming up because the linear 3.3 PS is not enabled. Gate voltage on Q102 is 8 V (what I've got my test supply set to). Gate voltage on Q101 is less than a volt. The 100k pull up resistor is in place, and the correct value.

Only thing I can see is the LIN_REG_EN output of the uP must be pulling it low (before the uP has enough voltage to run!) Checked for shorts, nada -- 80-100k.

Have I missed something? Any suggestions? Is the uP defective somehow, and how did it get that way when it was working, albeit strangely, before?

TIA for any suggestions!

A very frustrated,
Paul -- AI7JR

It seems to be ok so far, firmware loaded and the display is working.??

Thanks Jeffrey,

I found a solder whisker bridge from the plug in PCB#1 edge connector to the FET.? It turns on with the switch now, I hope there isn't any damage to the CPU.

IT's ALIVE!!!

The QMX hears and transmits as well! (Ironically the 1st thing it heard was from the QRP-Labs SigGen!)

On transmit without any adjustments at ~12VDC? into my QRPoMeter dummy load I measured:

80m?? 4.1W
60????? 4.0
40????? 4.1
30????? 3.7
20????? 3.5

Now to start setting the rig up!! I may even need to print out the operating manual!

--
73, Rick
VE7TK

Website:

I have the same question Hans. Is it possible for invoice 72091 to be made for 9V?

Rick, was not an issue with the inductor/ pin 3, just brighter than I wanted.?
--
73, Dan? NM3A

I'm just adding the #QMX hashtag, which I'd inadvertently left off. ?Thank you again in advance for any troubleshooting advice regarding the ~10ohm resistance detected across some of the A and B test points on step 12 (pg 31 with results re-attached). ?Best, Garrett KC3UNP

Just put in a 120 ohm (leaded) in place of the 33 ohm. Much softer and it's fine, but could have even gone to 150 or 180. Thanks for the info.?

BTW, I did not remove the 33 ohm, I just cut the one trace from the 33ohm to the pad.?
--
73, Dan? NM3A

Update: Definitely a toasted zener on the 3.3V PSU board.

Hooked up 3.3 board to bench supply. High current draw, zener gets hot. Removed zener. Current draw now reasonable. Installed 3.3 board into motherboard. Connected JP101 pin 8 to to JP201 pin 8 to trick CPU into thinking 5v rail is healthy. Connected bench supply to JP101 pins 4 and 2. CPU seems happy, I see PWM on the PSU PWM pins. If anything powered by 3.3 failed it didn't fail short. Still waiting on my buddy with the thermal camera to see if I can ID what failed short on the 5V rail.

First fire up on QDX 20-10. Led flashes normally. L4 started smoking. Yikes!
Now terminal shows only 80m, no other bands. Wsjt works into 50 ohms but usb sketchy
Replaced L4. Removed Diodes D1 and D4, they were shorted.
Where to next?

4 watts vs 3 watts is 1.25 db. IMO there are bigger fish to fry.

I intend to run off a car battery inverter so I took some extra steps to ensure thermal performance at 13.8 vs. 12. I put thermal paste between the bss170s and the ground plane, and a thermal pad on top to try and conduct more heat into the washer holding them down. Maybe at some point ill replace the washer with an aluminum bracket that attaches to the inside of the enclosure to conduct the heat out that way.

We'll see how it works when I figure out what I blew up in it...

My QDX was working fine until I was attempting to use it to drive a 100 watt HF amplifier. ?That amp failed, spectacularly, and now the QDX has these symptoms —
1. RX is good on all bands, with decodes appearing properly?
2. ?RX RSSI bar graph previously read (typically) 35-40 dB and was green, now reads 10 dB and is red.?
3. ? RX filter sweep is normal for all 4 filters
4. ?Attempts to transmit instantly shuts down the 9 volt 1 amp power supply after which the QDX restarts with the 5 second sequence and returns to normal receiver operating, albeit low sensitivity ??

I assume something in the common path is damaged such as the LPF switching, T/R switch or perhaps the transmitter final(s). ?

Suggestions for troubleshooting and fault isolation?

N6JH

?

Yup! Looking forward to the 'with' results!
--
73, Dan? NM3A