EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: hgg on February 10, 2018, 01:52:53 pm
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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 is
somewhere else because when I press the reset button all segments
light up for a second.
Do you know what kind of fault could cause this problem?
https://youtu.be/G-xh-GtNfxo
In the above video I am charging it and what you should normally see
at this point is a flashing 82%.
Below it displays a 100% charge.
(https://s5.postimg.org/kr4n4jxyv/Power_Bank.jpg) (https://postimages.org/)
I like this power bank because except from the 2 USB ports it
also have a DC barrel connector with variable 5-12V output.
Thanks.
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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!
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Hi,
The first is not a photo, its a video and you are supposed to see the
charging percentage %82 flashing, that's why it looks like a whole
digit is dead.
In the picture following, the number 100 is supposed to be displayed
but the top half segments are not displayed at all.
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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.
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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.
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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 charging
cable they start to switch on and off at random intervals.
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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.
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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?
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Indeed seems like a problem with the multiplexing.
Here is a photo of the board.
(https://i.postimg.cc/SRC28zcK/Power-Bank-QD184-SX-a.jpg) (https://postimg.cc/H8Wk1nZG)
The top IC is unmarked.. and the bottom is an 8-bit shift register 74HC595D.