Random negative readings on non-attached ports on mini v3

[NeoAddix]

Happy to have joined the WlanThermo tribe and I enjoyed building my mini v3 a lot! It is very cool

Before I explain my problem I would like to say that I'm not the best at soldering so I expect the problem to be somewhere there since I soldered the board myself. But if the problem is in the soldering I could use some help with where to focus.

The problem: as can be seen in the linked video; I get random negative readings from ports that do not have a sensor attached to it. It seems to apply to all ports (sometimes this one other times another one).

Any idea of what to look for?

Thanks (and if you are more comfortable with answering in German please do so, I'll use Google translate)

Jeroen

Link to vide:

 

[s.ochs]

Hi Jeroen,

you welcome!
Please share a good picture of the soldered PCB. Looks like a leakage current problem.
What does your soldering equipment look like? Was a lot of flux used? If so, was the circuit board cleaned afterwards?

Steffen

 

[NeoAddix]

Please don't laug at my soldering ;-)

I cleaned the PCB with alcohol first and used regular soldering tin. I have an old Weller station with a thin tip

Jeroen

 

[s.ochs]

Thanks! Unfortunately the solder joints don't look that nice. What about C7? The stabilization of the reference voltage is missing, that could also be the cause.

 

[NeoAddix]

Yeah, I'm aware of the mess. I'll try C7 and also ask a friend of mine who is good at soldering to help and see what we can rescue

 

[s.ochs]

Please check C7 first. The error pattern indicates a problem with the reference voltage.

 

[NeoAddix]

Put C7 in and it works! No more negative readings!!
Excellent, ready for summer

Thanks for the help

 

[s.ochs]

You welcome. Cheers!