Hello,

my Plus4 has gone berserk! I've attached a short video of the weird behaviour it's recently developed.
As you can see, it seems a JOG button is constantly depressed, but it's not! I've also checked all button with an ohmmeter and they are fine.

What's even more confusing is that it's working perfectly fine when controlled by NanoVNA-QT!

I've tried desoldering the "touch" pins of the display connector to disable the touch input, but that didn't fix it.

I've also tried different firmware releases, but that didn't solve it either.

Could anyone help me diagnose and fix this issue?

Cheers

Maybe the enclosure is pressing on the button? Any visible shorts on the button pins to the MCU?

> Il giorno 01 lug 2021, alle ore 18:29, OwO <OwOwOwOwO123@outlook.com> ha scritto:
>
> Maybe the enclosure is pressing on the button? Any visible shorts on the button pins to the MCU?

Neither, unfortunately. If I test the buttons contacts with an ohmmeter, they work as expected.

Cheers

You can message the seller for a replacement under warranty.
________________________________

> Il giorno 02 lug 2021, alle ore 15:25, OwO <OwOwOwOwO123@outlook.com> ha scritto:
>
> You can message the seller for a replacement under warranty.

I will, but this is already a replacement board (last time was a blown MXD8641)! It’d be nice to know the root cause.

Cheers

It's most likely soldering issue on the MCU (U303). You can try adding flux to it and drag solder with a normal soldering iron.
________________________________

MXD8641 issue is caused by ESD. Make sure to discharge the antenna before connecting a large antenna or long coax cable.
________________________________

> Il giorno 02 lug 2021, alle ore 15:34, OwO <OwOwOwOwO123@outlook.com> ha scritto:
>
> It's most likely soldering issue on the MCU (U303). You can try adding flux to it and drag solder with a normal soldering iron.

Thanks, I’ll try that!

Cheers

> Il giorno 02 lug 2021, alle ore 15:38, OwO <OwOwOwOwO123@outlook.com> ha scritto:
>
> MXD8641 issue is caused by ESD. Make sure to discharge the antenna before connecting a large antenna or long coax cable.

You’re right, in that case I was measuring a UHF collinear encased in a plastic tube hand-held. What I didn’t know at the time was that the MXD8641 is only rated 1000 Vdc or so…

Cheers

On 7/2/21 6:46 AM, Andrea Massucco IZ1IVA wrote:
>> Il giorno 02 lug 2021, alle ore 15:38, OwO <OwOwOwOwO123@outlook.com> ha scritto:
>>
>> MXD8641 issue is caused by ESD. Make sure to discharge the antenna before connecting a large antenna or long coax cable.
> You’re right, in that case I was measuring a UHF collinear encased in a plastic tube hand-held. What I didn’t know at the time was that the MXD8641 is only rated 1000 Vdc or so…

1000 V HBM is actually pretty rugged ESD wise (and the data sheet says
"ESD protected")

The problem is that HBM assumes you've got a resistor (the human body)
in series to limit the current.  Probably a better rating to look at is
the Machine Model or Charged Device Model.  MM is zero ohms and 0.5 uH
discharging a 200pF cap. so that's probably closer to what "coax to an
antenna" looks like.

MM rating is 100V -

On Fri, Jul 2, 2021 at 06:08 PM, Jim Lux wrote:

> 1000 V HBM is actually pretty rugged ESD wise (and the data sheet says "ESD
> protected")

I'm not an expert in ESD, I'm just reporting that I never had a similar issue with other amateur analyzers such as MFJ (ugh!) and RigExpert, so my empirical evidence says that perhaps 1000 Vdc may be insufficient. But then I might be wrong.

Cheers

On 7/3/21 5:15 AM, Andrea Massucco IZ1IVA wrote:
> On Fri, Jul 2, 2021 at 06:08 PM, Jim Lux wrote:
>
>> 1000 V HBM is actually pretty rugged ESD wise (and the data sheet says "ESD
>> protected")
> I'm not an expert in ESD, I'm just reporting that I never had a similar issue with other amateur analyzers such as MFJ (ugh!) and RigExpert, so my empirical evidence says that perhaps 1000 Vdc may be insufficient. But then I might be wrong.


Yeah - the MFJ is pretty good on static - the input feeds into a pretty
simple bridge with 1n34 diodes, but there are plenty of reports of the
front end being blown by strong local AM transmitters, for instance.

Here it feeds into a Silicon on Insulator switch, open circuit (no load)
so it's inherently more sensitive.

Any time you're hooking up test equipment to a big anything, those are
the sorts of issues you run into.

On Sat, Jul 3, 2021 at 03:16 PM, Jim Lux wrote:

> Any time you're hooking up test equipment to a big anything, those are the
> sorts of issues you run into.

I understand Jim, but in that case it was a small 868 MHz collinear in plastic tube hand-held, so my guess is that my hand charged it up the tube by rubbing against it. It's not like it was a 160 metres dipole a half-wave above the desert HI!

On 7/3/21 11:07 AM, Andrea Massucco IZ1IVA wrote:
> On Sat, Jul 3, 2021 at 03:16 PM, Jim Lux wrote:
>
>> Any time you're hooking up test equipment to a big anything, those are the
>> sorts of issues you run into.
> I understand Jim, but in that case it was a small 868 MHz collinear in plastic tube hand-held, so my guess is that my hand charged it up the tube by rubbing against it. It's not like it was a 160 metres dipole a half-wave above the desert HI!


yeah, but that colinear was probably a meter long and a few cm around,
so it was tens of pF, and you charged it to several thousand volts.

(1m, 2cm diameter is 15.4 pF)

You can get remarkably large charge storage on a fairly small object,
especially if the radius of curvature is large (max potential is 3E6
V/m, so 1cm radius - not so big - can charge to 30kV)

What blows up the device is the peak current (and to a lesser extent,
the energy), and as the voltage goes up, the peak current goes up.  In
fuses, one speaks of the "action" measured in Amps^2 * seconds. 
Doubling the voltage makes the action 4 times larger.

> Il giorno 03 lug 2021, alle ore 20:52, Jim Lux <jim@luxfamily.com> ha scritto:
>
> You can get remarkably large charge storage on a fairly small object, especially if the radius of curvature is large (max potential is 3E6 V/m, so 1cm radius - not so big - can charge to 30kV)

I wasn’t expecting that much!

Yeah, the main issue is that the antenna is not shorted for DC, a major design flaw in my opinion.

Cheers

On 7/5/21 1:40 AM, Andrea Massucco IZ1IVA wrote:
>> Il giorno 03 lug 2021, alle ore 20:52, Jim Lux <jim@luxfamily.com> ha scritto:
>>
>> You can get remarkably large charge storage on a fairly small object, especially if the radius of curvature is large (max potential is 3E6 V/m, so 1cm radius - not so big - can charge to 30kV)
> I wasn’t expecting that much!
>
> Yeah, the main issue is that the antenna is not shorted for DC, a major design flaw in my opinion.
>
> Cheers


Even if shorted for DC, the "entire antenna" can wind up being charged.