Purchased my VNA on Tindie. It has been working well but now it's broken below 140MHz - I suspect the SI5351 circuit... Above 140 it's working as it shoud be (LED401 and LED601 light blue), measurements fine doing S11 or S21. Below that - "spaghetti" as someone wrote in earlier threads.

Looking at the v2.2 circuit diagram (which v2.4 is similar I suppose) there should be some clock signal on CLK0, CLK2 on SI5351 chip when doing sweep between 100-100.1MHz for example - there is not. VDD is 3.0V, there are some signals on SDA and SCL lines... 24MHz oscillator works.

Any ideas?

Same issue in my Nanovna V2plus4. I hope someone can find any solution....

Stefano, have you checked the SI5351 outputs somehow, or you just observe the same problem?
I'm not an expert, but got quite good skills with soldering such small SMD like those MXD switches, got the oscilloscope but not having the exact circuit diagram and part placement on PCB (which is multilayer I think) is big problem to diagnose the failure.

May I ask you to share the photo of the bottom layer of the PCB (which is the opposite to MCU is mounted on)? On mine there are 4 pads, where is a place for 2 SMD components which may have felt off (I'm not sure if there were anything before).

The other susspice may be some failure in SI5351 initializing, which could lead to not generating any CLKx signals - if that is the case there should be some firmware related fix possible... Got no possibility to check the IC at the moment, but I plan to desolder and check it in an external circuit soon (I also got a few spare SI-s but they are marked a bit else and I'm not positive I can swap them just like that).

Anyone able to help somehow? Anyone from VNA Team?

Hi, if you bought your VNA from our official store, please click "Contact Seller" and include your order number for warranty service. A few early units had soldering defects, and we are still trying to track them down. In the early days we were under a lot of cost pressure from trying to compete on price when there is a lot of predatory pricing on the market, which was the biggest mistake we have made. In 2022 we started switching to better suppliers and assembly services, but if you have an earlier unit with issues, please don't hesitate to contact us to get it repaired or replaced. We are on holidays at the moment and will return and be able to assist you in about one week.
Thanks,
NanoRFE support

Comment savoir si on a acheté un produit original ? J ai acheté le mien
chez Ali express .

Help us

French user

Le jeu. 27 avr. 2023 à 07:37, nanov2support <edelswartz123@gmail.com> a
écrit :

> Hi, if you bought your VNA from our official store, please click "Contact
> Seller" and include your order number for warranty service. A few early
> units had soldering defects, and we are still trying to track them down. In
> the early days we were under a lot of cost pressure from trying to compete
> on price when there is a lot of predatory pricing on the market, which was
> the biggest mistake we have made. In 2022 we started switching to better
> suppliers and assembly services, but if you have an earlier unit with
> issues, please don't hesitate to contact us to get it repaired or replaced.
> We are on holidays at the moment and will return and be able to assist you
> in about one week.
> Thanks,
> NanoRFE support
>
>
>

Hi Fabrice, unfortunately almost all on Aliexpress and Amazon are clones, there is only a small percentage of sellers that have bought from us, can you tell me which store you ordered from?
Thanks

Hi,

Merci pour ja réponse mais le texte est illisible …
I can try
Qiaejiaeo peut être ?!?!

Analyser e19838*1

Je crois que ça fonctionne bien mais je le demande comment mesurer le swr d
une ce antenne fd4 et son câble … il faut des adaptateurs

Cordialement

Le jeu. 27 avr. 2023 à 08:01, nanov2support <edelswartz123@gmail.com> a
écrit :

> Hi Fabrice, unfortunately almost all on Aliexpress and Amazon are clones,
> there is only a small percentage of sellers that have bought from us, can
> you tell me which store you ordered from?
> Thanks
>
>
>

I was having the exact same issue with Si5351. In my case, the voltage output at one of SCL or SDA (don't remember which) was not being generated by the microcontroller. After a lot of research, I figured out that the particular IO on the microcontroller chip was damaged --> it could not pull the I2C voltage to 0V, therefore failing to program Si5351.

The Si5351 was in fact fine. I knew it by replacing the microcontroller and flash the ROM from the original microcontroller. I saw some correct output from Si5351, so it was fine. No issue with Si5351.

However, unfortunately, due to the bootloader lock, my device (v2 Plus4) couldn't work anymore, as the device ID of the microcontrollers are different. The bootloader check for this device ID and if it's not correct, it will refuse to do measurement.

Fortunately, I contacted Tindie and they were nice enough to send a replacement.

Finally my NanoVNA V2 Plus4 is working again. I have contacted the HCXQS group on Tindie as someone suggested and they have agreed to repair the PCB. The faulty part was microcontroller, which has been replaced and now the analyzer is working full band.

Thanks HCXQS group, good job!

I have the same problem (below 140 MHz the results look like spaghetti).  I purchased one of the very early NanoVNA V2 Plus4, back in December of 2020.  At the time it was available via AliExpress on the "NanoRFE Store" so that is where I purchased it from.  My recollection is that it was being sold before there was any silk-screen on the enclosure and so I accepted that.

Is there any way to get it fixed?

I haven't tried looking at the SCL or SDA lines on the Si5351 yet.  Perhaps they need pull-up resistors to work reliably or ??

I also have not tried to upgrade the firmware to see if a newer version changes anything.

When it worked it was great.  I hope to get it repaired.  Thanks!

Best would be to buy a new one from the authorized source. The cost to
have someone repair it for you would likely exceed the cost of a new one.
Everything is more expensive now.

On Thu, Jul 3, 2025 at 1:00 AM Paul Danilchik / NT7U via groups.io <nt7u=
vectorforward.com@groups.io> wrote:

> I have the same problem (below 140 MHz the results look like spaghetti).
> I purchased one of the very early NanoVNA V2 Plus4, back in December of
> 2020. At the time it was available via AliExpress on the "NanoRFE Store"
> so that is where I purchased it from. My recollection is that it was being
> sold before there was any silk-screen on the enclosure and so I accepted
> that.
>
> Is there any way to get it fixed?
>
> I haven't tried looking at the SCL or SDA lines on the Si5351 yet.
> Perhaps they need pull-up resistors to work reliably or ??
>
> I also have not tried to upgrade the firmware to see if a newer version
> changes anything.
>
> When it worked it was great. I hope to get it repaired. Thanks!
>
>
>

I hear what you are saying but I don't throw away things that should be repairable.  Despite being easily able to afford another one, it's not in my DNA.  And if that replacement one fails, then what?

I received a direct reply from the seller instructing me to re-solder U502 which is the Si5351 chip.  That sounded reasonable so I examined that device under a stereo optical microscope and while the solder joints to the chip leads looked good, I resoldered all ten of them none the less.  However, that did not fix the problem.

My guess is that perhaps one of the MXD8641 rf switch chips has gone bad.  If for the frequencies below 140MHz the Si5351 clocks were not being switched in place of the ADF4350 clocks then it might result in the issue that I'm seeing.

I am waiting to hear back from the seller and pondering if I should solder some thin wire-wrap wire to various points enabling me to probe signals with my digital oscilloscope.  I do have the schematic.  Ideally though someone with some insight might clue me in to what issues or vulnerabilities exist in this product such that it might get me to the solution faster.  Does anyone have technical insights such as what might be amiss that results in the readings below 140MHz being all over the place??

Thanks kindly, Paul