Flux causing high resistance short?

[evilkitty]

Now that my de-soldering gun is working i was able to remove this panel i made about a week before i noticed a issue the F segment of digits 2 and 3 would go out, digit 2 would go before digit 3, but would come back after the humidity got down from running the ac (note the weather outside is 30.5 / 74%; panel data is from a BME280)


Temp is on the left humidity is on the right

i noticed when the humidity got up one or 2 of the center digits on the right panel would loose a segment

The pin out looking down from the top is (note this is common cathode)

1 A F 2 3 B

E D . C G 4

upon taking my meter to it i found 40-100k resistance between the cathode of pins labeled 2 and 3 (should be NC), it would also read as a defective capacitor
got it off the board and checked the pins and got near 100k, noticed what looked like some flux around the base of the pins on the part, cleaned it off and resistance is gone
is the crappy flux from the hardware store absorbing humidity and becoming conductive? maybe is was flux from my solder?

[stj]

all flux absorbs moisture - if your in a humid place you need to remove it.
i wouldnt say it shorts, but it creates enough capacitance to effect stuff like ram chips!

[redwire]

If F segments go out on the inside two digits but not the outside ones, it's not a short circuit but is an open circuit on the internal bus of the LED display for the inside digits F.
It could very well be corrosion/contamination due to extra flux or water (factory) wash inside is what I think. It might be why the displays were cheap. Which store did you buy them from?

[evilkitty]

I think this is the one: https://www.aliexpress.us/item/3256805956739680.html

the other F segments in the array get brighter when it acted up, F Pin is next to the other 2 affected pins, and it is was working fine on my breadboard last night, gonna need more testing though to be sure it was a internal issue

controlled via a MAX7219 from the same supplier

i do agree it looks like a open circuit as if there was a short the other F segments should have gotten dimmer not birghter

[redwire]

I would say the display has issues inside, heat from soldering can make it worse or better. High resistance is usually water or corrosion, which takes a little while to make things croak open circuit.
You can try push/squish the display too with a finger and see if it's tough enough.

Quality is hard to know these Ali stores have many shells, repeatedly shut down then reopen. Many are just booths in the SEG Plaza.
IGMOPNRQ/shenzen IC
IGMOPRNQ/Microelectronics Technology Co.
IGMOPNRQ Component parts Store

I tried LED displays from JUHIWOR SCIENCE Store and they are medium quality, they work and low price.
High quality ones I bought, have to dig for the store name. Chanzon is expensive but high quality.

edit: also there are bugs in many BME280 libraries, you have to wait until it loads its own cal coefficients before reading it. It was like adding a 10msec delay was good enough on power up.

[evilkitty]

I have not had issues reading the sensor, but i do not trust the humidity reading, my DHT22s all read around 10% higher, not sure what sensor is full of it (DHT22 ~25C = 99%; BME280 ~25C= 77%; weather says 26C @ 89%)
note that all of my sensors are from cheap places, my dht22s were $1 each on ebay, got every unit the seller had

seems to be working on my breadboard at these much worse humidity levels, will give it a while b4 i re-solder it

this is the lib i am using: https://github.com/mbuesch/bme280-upy

[CapLeaker]

note that all of my sensors are from cheap places, my dht22s were $1 each on ebay, got every unit the seller had

seems to be working on my breadboard at these much worse humidity levels, will give it a while b4 i re-solder it

this is the lib i am using: https://github.com/mbuesch/bme280-upy

Probably they are rejects and sold on fleabay, Ali, etc. as original factory part.

[evilkitty]

Probably they are rejects and sold on fleabay, Ali, etc. as original factory part.

apparently you can recondition them with ~5 days of 25C and > 40% humidity
well i do not think that will be hard to do...

[sam_sam_sam]

apparently you can recondition them with ~5 days of 25C and > 40% humidity
well i do not think that will be hard to do...

Probably not hard to do but after a certain amount time has passed the question is whether or not the issue will return or is the issue really solved

[evilkitty]

well leaving them in the garage for that week+ did not seem to affect the reading, that said right now at my desk the humidity reading is very close to what my nearest DHT22 reads (within margin of error for the sensors), the one i have in the garage i do not trust the humidity reading of, last i checked it was reading +20% compared to the BME280, maybe the horrible humidity skewed it's reading, the one in the attic does not have reading at high, but that one gets heated up a lot in the day while the one in the garage just gets warm and stays near the same temp and gets the humidity this area shoves at it

after cleaning the panel and leaving it in my breadboard for a few weeks in the garage it did not do the same thing, i have it back on my prototyping board now