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

开云体育

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Chris, G5CTH

Chris, is this with or w/o Zeners?
--
73, Dan? NM3A

The short is somewhere on the main board, verified by pulling out the PSUs and testing each board individually. I wish the PSU was the problem since it's easier to just order another power module than to troubleshoot a very dense main board with a bunch of very tedious labor put into it that I'd rather not repeat... As it is I'm going to borrow a thermal camera from a friend and see what heats up when I try to power up. I live pretty close to a digikey warehouse so I can get pretty quick shipping on replacements.

I'm willing to bet the failure went something like this -

* Bench supply goes into current limit, drops input voltage
* Duty cycle of buck regulators increase
* Bench supply comes out of current limit when TX ends, input voltage comes back up
* Known issue with CPU failing to respond to transients in input voltage fast enough to prevent rails from spiking
* Protection zeners fail open? I don't see any shorts in PSU boards
* Op amps are probably fine since they're all 30 volt parts, but the Tayloe detector, ADC, DAC, and LCD are all liable to have been killed by this.

I would propose the following modification to the power circuit to help prevent this issue:

https://photos.app.goo.gl/shkveUjM5gU6WNqP8

This would shut down the pwm in an overvoltage event much faster than the cpu can.

The ultimate solution would be to use an off the shelf buck converter IC with a frequency synchronization feature. An IC whose control loop runs as fast as its pwm will naturally have better impulse response than a CPU running a control loop at 1khz.

I think it's just a matter of being cautious.

I use an Elecraft T1 to tune but use a tuning indicator (TI) that
ensures no more that 2:1 swr is presented to the rig. I have forgotten
to put the TI in tune mode more than once. All it takes is 1 bad
mismatch and maybe I kiss my finals goodbye. I'd rather not replace
them if I can avoid it. Since Hans puts it in big bold red letters to
not go over 12.0v I'm gonna listen... maybe necessary, maybe not...

Until I'm fully comfortable that these rigs are indeed robust, I'm
erring on the side of caution.

-mike/w1mt

Why would 5W at exactly 9V, for the 9V version be ok, but 5W at exactly 13V, for the 12V version, be dangerous? FWIW, I’ve ran my QMX off a LiFePO4, transmitting with as high as 13.8V, but mostly in the 13.2-13.3V range, with no problems. But to be fair, I’m using a manual tuner. ?But again, it borderline feels like what I’m reading, on a near daily basis, is running more than 4W at 12V is a sin.?