Power Bank 7 Segment Display Fault - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: February 10, 2018, 01:52:53 pm
content: Hi,I have been using this power bank for many months without a problem.Recently the 7 segment display stopped displaying all segments.I have re-flowed the display pins but it looks like that the problem issomewhere else because when I press the reset button all segmentslight up for a second.Do you know what kind of fault could cause this problem?https://youtu.be/G-xh-GtNfxoIn the above video I am charging it and what you should normally seeat this point is a flashing 82%.Below it displays a 100% charge.I like this power bank because except from the 2 USB ports italso have a DC barrel connector with variable 5-12V output.Thanks.

author: SL4P
author_rank: Super Contributor
timestamp: February 10, 2018, 06:30:13 pm
content: It looks like your photos display two different symptoms... which in turn suggests a driver issue, but that’s an early guess because your words don’t reflect that.In photo 1 it looks like a whole digit is dead, and the middle ‘g’ segment is missing on only one digit, while photo #2 seems to suggest four segments are missing from both digits...Reflowing was a good start, but you may be looking at a cracked pcb track(s),or more subtle fault.What are the two,photos ‘meant’ to be Displaying!

author: hgg
author_rank: Frequent Contributor
timestamp: February 10, 2018, 06:58:46 pm
content: Hi,The first is not a photo, its a video and you are supposed to see thecharging percentage %82 flashing, that's why it looks like a wholedigit is dead.In the picture following, the number 100 is supposed to be displayedbut the top half segments are not displayed at all.

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 10, 2018, 07:22:53 pm
content: It's probably not a continuity problem. That would only be affected by movent and would be random. This seems like systematic incorrect lighting of the digits. The chip is probably fried.

author: Nusa
author_rank: Super Contributor
timestamp: February 10, 2018, 07:23:41 pm
content: Try pressing on the reset switch body without actually pressing the switch. If the behavior changes, you've got a cracked trace or solder joint somewhere.

author: hgg
author_rank: Frequent Contributor
timestamp: February 10, 2018, 07:31:10 pm
content: Nusa I've just tried pressing the reset button body but nothing changes.I've tried pressing on all the components on the board.Cyberdragon do you mean the display driver chip is fried?The top half of the segments are off but when I connect the chargingcable they start to switch on and off at random intervals.

author: Cyberdragon
author_rank: Super Contributor
timestamp: February 10, 2018, 08:11:34 pm
content: Yeah the chip is dead if it does that. The nail in the coffin for it is the fact that you said it's supposed to flash the percentage, but only one digit was. The other two were stuck on, meaning a short somewhere. Is there a seperate CPU and driver or is it just one chip? If it's just one chip, it's done for, as replacing it would lose the code. With something simple like this, you could try to make your own replacement code if you want to bother with it.

author: SL4P
author_rank: Super Contributor
timestamp: February 10, 2018, 09:14:54 pm
content: Sorry about the ref to a ‘photo’ - it was very late at night...!If not fried (quite likely), is there a chance the electronics have been wet or contaminated?Perhaps some juice or slime under the display driver! After watching the ‘video’ it seems like an issuerelated to multiplexing... (and very slow muxing at that)How about soaking the display driver / whole board with IPA and then a soft toothbrush?

author: hgg
author_rank: Frequent Contributor
timestamp: February 11, 2018, 07:30:17 am
content: Indeed seems like a problem with the multiplexing.Here is a photo of the board.The top IC is unmarked.. and the bottom is an 8-bit shift register 74HC595D.