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I believe that your problem is a bad battery that won't take a charge,
therefore, it wont start either!


V. Kaufman

I have a smaller one that the screen was damaged so maybe I will have spare parts.
I’m I did check the resistors the other day and showed good.
I will see it I can find that schematic so figure out what tbe SA16 part you mentioned, I do have a heat gun so can use the to remove parts

On 2/17/22 3:41 PM, Jim Lux wrote:

On 2/17/22 12:57 PM, Larry Rothman wrote:

? Alan,
The schematics are in the Wiki.
There are only resistors in the input pad. You need to measure them to see which is fried. Hopefully, you didn't fry the SA612 input.

If you have 2 soldering irons with fine tips, you can lift each off the board easily but remember the display is on the other side of the PCB - so not too much heat.
It's not that hard - I flipped the resistors on my Nano-H to see if it helped with the noise (msg thread on that in 2019).
If you have a junk box, you might be able to find replace SMT resistors on scrap boards.

???? On Thursday, February 17, 2022, 03:44:55 p.m. EST, Alan Brown via groups.io <va3aqb@...> wrote:
? ? So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?

The resistors are cheap, too. I just heat them, and scrape them off with an xacto knife.? Before surgery, you can check: If you cooked one, the resistance will be wrong.? The SA612 is DC blocked, so you can calculate what DC resistance you should see from the CH1 connector (56 ohms , in parallel with 2*240+50 ohms - probably pretty close to 50 ohms)

I just measured about 50.5 ohms dc resistance.

On 2/17/22 12:57 PM, Larry Rothman wrote:

Alan,
The schematics are in the Wiki.
There are only resistors in the input pad. You need to measure them to see which is fried. Hopefully, you didn't fry the SA612 input.

If you have 2 soldering irons with fine tips, you can lift each off the board easily but remember the display is on the other side of the PCB - so not too much heat.
It's not that hard - I flipped the resistors on my Nano-H to see if it helped with the noise (msg thread on that in 2019).
If you have a junk box, you might be able to find replace SMT resistors on scrap boards.

On Thursday, February 17, 2022, 03:44:55 p.m. EST, Alan Brown via groups.io <va3aqb@...> wrote:
So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?

The resistors are cheap, too. I just heat them, and scrape them off with an xacto knife.? Before surgery, you can check: If you cooked one, the resistance will be wrong.? The SA612 is DC blocked, so you can calculate what DC resistance you should see from the CH1 connector (56 ohms , in parallel with 2*240+50 ohms - probably pretty close to 50 ohms)

On 2/17/22 12:44 PM, Alan Brown via groups.io wrote:

So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?

As previously described, (see attached schematic ) there's a resistive pad (E2, R22,R23,R24, R25) then the SA612AD ( E4, U8.) I doubt it would blow up anything else that's connected (that is, the SA612 protects the ADC in U9)

I don't have the -H4 schematic handy, but it's similar (the big difference is the screen size).

Check the rocket switch with an ohmmeter to verify all 3 switches are normally open.


On Thu., 17 Feb. 2022 at 4:32 p.m., Brady Nelson<tbradynelson@...> wrote: I did have some trouble with the button when it was working, but I keep messing with the button to see if I can get it to start, no luck.

On Thu, Feb 17, 2022 at 12:44 PM, Alan Brown wrote:

So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds
and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most
things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is
to high?

I posted the schematics in the other post you made on this subject..

Roger

I did have some trouble with the button when it was working, but I keep messing with the button to see if I can get it to start, no luck.

I blew my vna after connection to a cheap digital attenuator, current surge
blew out front end. Use only passive fixed attenuators now.

On Thu, Feb 17, 2022, 3:55 PM Alan Brown via groups.io <va3aqb=
[email protected]> wrote:

So S21 has been damaged when I was checking a LNA, i gapped it for 2
seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most
things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input
is to high?

Alan,
The schematics are in the Wiki.
There are only resistors in the input pad. You need to measure them to see which is fried. Hopefully, you didn't fry the SA612 input.

If you have 2 soldering irons with fine tips, you can lift each off the board easily but remember the display is on the other side of the PCB - so not too much heat.
It's not that hard - I flipped the resistors on my Nano-H to see if it helped with the noise (msg thread on that in 2019).
If you have a junk box, you might be able to find replace SMT resistors on scrap boards.

So S21 has been damaged when I was checking a LNA, i gapped it for 2 seconds and hooked the attenuator on the wrong side.
It is a H4, I was going to order a new one as needed pass through on most things I use it for.
Anyone know how to fix, is there a diode or anything that blows when input is to high?

On 2/17/22 7:52 AM, William Smith wrote:

Just make sure, as others have pointed out, that you don’t have any other wires (power supply, USB to computer,, etc) connected to the nanoVNA.

I'm not sure a USB cable would make a difference if the feedline is properly "isolated" from the environment. (i.e. the USB cable isn't coiled up with the transmission line).
I can't think of a physical mechanism for that to cause a problem.

One could easily test it with the NanoVNA by itself, and then with the cables hooked up. If there no difference, then knock yourself out using a PC app to control the VNA.

73, Willie N1JBJ

On Feb 17, 2022, at 10:10 AM, Jim Lux <jim@...> wrote:

On 2/17/22 5:52 AM, WB2UAQ wrote:

We're measuring impedance here. No matching transformer is needed. Just a 1:1 high common mode Z balun. From the Z's measured you determine the characteristics of the balanced transmission line OR and that includes its electrical length. Let's not over complicate things here.

Considering that the NanoVNA is smaller than a lot of HF baluns for balanced lines, I don't think you need the balun, either (until you get up to where the NanoVNA is a significant fraction of a wavelength - maybe don't use it for UHF TV twinlead.

Sorry - that should be 3v at each of the points, not between.
Now, with that said, I just had weirdness with my Nano-H - it wouldn't boot.
It turned out the Enter button (I installed buttons on mine) was pushed-in.
Everything was fine when I un-stuck the button.
Check your rocker switch to make sure it's not stuck in as that would put your H4 into DFU mode with no display lit.

I measured it while unplugged from USB, I get 3.4V between VDD and Ground but no voltage between VDD and the capacitor in the picture.

The only thing at this point is to measure the VDD out of the 3v regulator to make sure it's working.
Schematics are in the Wiki.I've attached an early H4 PCB image for you.

Your battery is defective - get a new one or have a look at some of my early posts where I used a cellphone battery.
/g/nanovna-users/attachment/223/0/Battery-PCB-MiscShields.jpg

my nano vna Hugen v4 shows full battery but after about 10 seconds turn
off.... connected to USB port works fine

On Thu, Feb 17, 2022 at 10:35 AM Brady Nelson <tbradynelson@...>
wrote:

Hi All,

My Nano VNA-H will not turn on after charging. It had been sitting for a
while, so I assumed it was the dead battery, but after charging, the
battery is at a good voltage but the screen will not turn on. Doesn't want
to turn on via USB either. Any ideas what could be causing this?

Sorry should have been clearer, it doesn't turn on even with the battery disconnected.

Correct - that is controlled by the charging/inverter chip.
Can you turn your Nano turn on when connected to USB and the battery is disconnected?

Hi Larry,
When I disconnect the battery and plug the USB in the LED blinks as if it is charging.

sorry for double post, didn't realize my other one went though.