Almost zero send and receive - troubleshooting steps?

[Dirkus]

Hello everyone! Just built my first truSDX from a kit I got from Sunny in China. Great experience there, I’ll probably buy more stuff from them. The day I got my kit, I sat down and built the kit in one sitting over 2-3 hours, taking my time to get the toroids looking real nice and all that. I’ve done plenty of simple electronics before, built all kinds of strange contraptions, even internet enabled my old charcoal grill one time with a ESP8266 module, but I’ve never worked *directly* with the RF side of things. A lot of this is black magic to me.

What works: The radio powers on just fine. Was able to flash with my call sign. Display works. All buttons and the encoder work. Firmware is 2.00t.

What DOESN’T work: My TX power and RX sensitivity are almost zero. Even hooked up to a really nice antenna at the local ham club, I can only hear a faint whisper of signals that other station operators were picking up S9. This is true across all 5 bands (classical band RF board) And transmitting seems to do very little. Even with a fairly well matched antenna (1:1.3) a station less than 5 miles away could barely hear anything, and saw nothing on his waterfall.

Suspicion: Since it is the same across all bands, I suspect the issue is either in the RF generating side, or the SWR meter side, but not the LPFs. The unit does show output power that’s close to the specs and an SWR that isn’t too far from what an external SWR meter shows for the same antenna, so I *think* the RF side of things might be OK. Maybe.

A possible problem I may have is that as I was wrapping and soldering in the toroids, I was checking them with a multimeter to make sure I had good connections across them and didn’t accidentally have a bad solder joint from missing scraping off some lacquer. Could the voltage from the multimeter’s continuity check have cooked something? For instance, to test L11’s connection, I looked for continuity from C10/11 to C12/13. Was that a bad idea? If I did cook something doing that, what would it have been, and how can I tell?

Also, the SWR readings from the radio are slightly off from a high end external SWR meter. Is it possible I might have a short in T1 or T2 from me getting too aggressive while wrapping them? Can I remove T1 and T2, then jumper from pad 1 to pad 2 where T1 was to disable the SWR meter and check performance without the SWR transformers safely? Or would that cook something?

Thanks in advance for any help you can provide. I’m pretty frustrated with myself on this one.

My RF board.

IMG_3162.jpeg (167.21 KiB) Viewed 922 times

[Cthulhu]

Are you listening through the built-in speaker? Try listening on headphones or an external speaker

[Dirkus]

Are you listening through the built-in speaker? Try listening on headphones or an external speaker

Yes, I tried an external speaker AND headphones. Same with both of those. I know the onboard speaker is kinda weak, and I do plan to do the “howling speaker” fix, but that doesn’t explain the super weak transmit.

I think I’m going to risk it for the biscuit and try deleting the SWR transformers as a test. From my understanding, that shouldn’t change anything in the RF path too much, so I *shouldn’t* fry anything. If that works, I’ll have to see if I have enough leftover wire to re-wrap those. If it doesn’t work… uhhh… man I dunno. Again, RF is black magic to me at the moment.

[iw0dfd]

Hi Dirkus,
did your kit come with the smd fets for the PA section? I don't see the BS170 mounted.
Giuseppe

[Dirkus]

Hi Dirkus,
did your kit come with the smd fets for the PA section? I don't see the BS170 mounted.
Giuseppe

Yes, it did. The Classic RF board uses a surface mount PA FET on the back of the board instead of the BS170’s on the coil side. I’m only a “technician” class operator under the FCC licensing scheme at the moment, so I can only do SSB on 10 meters for now. That’s a problem I’m working on too!

[dl6sez]

Hello OM,

please find your solution here:
viewtopic.php?p=3244#p3244

73 de Chris

[Dirkus]

Hello OM,

please find your solution here:
viewtopic.php?p=3244#p3244

73 de Chris

Thanks for pointing me to that post, Chris!

Sadly I don’t have a signal generator, and my oscilloscope is a very cheap pocket sized unit that tops out at 1MHz. I *might* be able to borrow those items from a member of the local radio club, but that may take a while. The few things I could check with that guide are fine, but the rest are out of my reach at the moment.

I did find out something interesting though, while playing with an RTL-SDR dongle and my truSDX at the same time. Any frequency I tune the truSDX to receives a nice big spike of RF. It’s almost like the board is stuck in transmit. Wish I could attach a video of it. The moment I attach power and an antenna to the truSDX, a huge spike and several harmonics appear on my computer’s RTL-SDR.

So, that makes me wonder:

1) Is one or more of the drive MOSFETs faulty and constantly sending a drive signal to the PA FET?

b) If so, how can I test that theory?

3rd) If so, might that have cooked the detector?

IV) Does Sunny at NewDIYTech allow for a warranty on the main board, or am I going to have to get good at surface mount soldering Real Fast?

[Dirkus]

I figured out that the unit is indeed just transmitting constantly. This knowledge comes at the price of one DSO Shell oscilloscope, that apparently can't handle the RF this thing puts out. Keep in mind, I never touched the PTT/KEY button, this was just the unit sitting idle on my bench. I touched the o-scope probe to the RF pin on the board interconnect header, and that was all she wrote. Scope's done, won't even see its own 1kHz test tone lug any more.

This leads me to believe that YES, something is causing the unit to constantly drive the transmitter and YES, probably quite a few things are hosed on this unit. I've just wasted 100+ dollars. I'm gonna go to bed and reconsider my life choices now. Good night.

[Dirkus]

Took a moment to consider the situation last night.

Not sure why/how the o-scope cooked. It was rated for 50vpp, pretty sure the most I should see in the absolute worst case would be about 36vpp. (Pulsing 12v through one of the 1:3 transformers is the worst thing I could think of, but again RF is black magic to me) In any case, it’s toast. Thinking of replacing it with a Pokit Pro unless someone has a better suggestion.

It looks like DL2MAN and Sunny released the 1.2 main board the day after I ordered my kit. I might just spend the $48 for a whole new main board kit, and ask Sunny if he can throw in a loose PA FET for a buck or two while they’re at it. I’ll replace that first, then go for building the new main board.

Any other suggestions?

[Dirkus]

Thanks to a post from DL6SEZ in another troubleshooting thread, I was inspired to take a soldering iron to every pin on every IC on the main board. Considering my unsteady hand and the minuscule pins, this was a risky decision. Since I thought most of the ICs main board were fried anyway, I went for it.

IT WORKED!

I’m not sure which component had a floating pin, but now I can receive signals clearly, my transmissions seem much better, and even CAT control seems to work reliably.

Lessons learned:
- Don’t trust mass manufactured boards that haven’t been tested.
- Lead free solder is crap.
- Don’t connect a $38 oscilloscope to something that spits RF. It doesn’t like that.
- Don’t give up on a project, even if it seems like it’s toast.
- Flipping a Celestron telescope eyepiece backwards makes for an incredibly powerful and clear loupe.