I built my (tr)uSDX yesterday. Then it blew up!

[DB3BEF]

Hi everyone!

So, I got myself a (tr)uSDX kit from one of the official links, the ebay seller.

Yesterday I had found the time to finally finish it. I assembled everything, printed the case and put it in the case.

First things first, so I connected it to USB only and updated the firmware to the latest release. I noticed that the bottom was getting quite warm, even when not on TX. Later I found out, it was the Q2 FET.

Regardless, I continued testing. I also installed the latest beta, just in case that's relevant.

I hooked up my 50 Ohm 5W dummy load and TXed a bit, showing actually reasonable data.

Then I tried it with 13,8V external power. This is where it got a bit weird. I saw the display flashing on for a fraction of a second. Apart from that it was dead. However, when I powered it from USB and hooked up external power, it also would do more TX output, so it seems that it made use of the power.

I don't exactly know what it was that I tried, but I eventually hooked it up to 13,8V again and it suddenly would become alive trough 13,8V. I just got weird power readings.

While NOT TXing, it suddenly went "bang". I disconnected everything and opened the case, just to see that the Q2 FET blew up and split in half.

I have no clue what actually happened. I would assume that Q2 is not supposed to become that hot, especially when on RX only on USB power?

Any hints for troubleshooting would be highly appreciated!

Cheers

DB3BEF

[DB3BEF]

I have made some photos. Not sure if you can see anything because of the file size limit

[DB3BEF]

I was in the ham radio club today and we did some experimenting.

First of, all 3 BS170 are connected in parallel, so just one of them getting hot and/or blowing up doesn't make sense, kind of. We de-soldered Q2 and replaced it with Q3. This time, Q2 (ex Q3) didn't get hot.

Maybe I killed it with static somehow or it was faulty from the start.

Regardless, I will now go for a FDT86256 instead, removing the BS170s alltogether.

Hope that will fix it.

[Luca66]

Hello
I'll just ask you one question..... Before you started using the trusdx, did you calibrate the rf board filters?
73 Luca

[DB3BEF]

Hm, I'm not sure what you mean by calibrating the filters? The defective BS170 got quite warm when I flashed the firmware, and that's pretty much the first thing you do.

[Luca66]

The trusdx, despite being an easy construction kit, requires a first calibration of the low pasda filters for the second order harmonics and for each band, followed by the adjustment to the output power.Look here

https://dl2man.de/2-trusdx-assembly/

At the bottom of the page there is a video that shows in practice the filters tuning.

73 Luca

[KE0QQQ]

Hello world,
i hope all is well.. I have made 4 of these things and have had a chance to make nearly every mistake.
I have have bad BS170's from the bag. Yep, they get hot hot hot. No explosions yet. I clipped the hot one and completed a camping weekend once using 2 fets.

Chances are if you search and read all my previous posts, there is enough there to rise above and make this a nifty little rig. Once I learned to add the zener diode, despite our creators advice, I have not popped another final.

https://forum.dl2man.de/search.php?keyw ... mit=Search

Well once, I left it on 17m with a 15m dipole. I completed 2 QSO's at 7:1 SWR before one gave up. My fault. Tiny dim displays for a tiny dim mind

Why are there soooo many viewers watching this forum today ????
Is there a new model coming out?
Did DL2MAN win an award ?? hi hi

[DB3BEF]

https://dl2man.de/2-trusdx-assembly/

At the bottom of the page there is a video that shows in practice the filters tuning.

Thanks, I'm watching the video right now. I have removed the BS170 and replaced them with a FDT86256 today. What can I say, power is as expected, around 5W in all bands on 12V. Nice.