Hello!

I just registered here and started reading some of the high level threads going on here, and I am left with the impression that asking for your help and advice is like calling out the firetruck to put out a matchstick.
Nevertheless, I have read the fixed thread on opening new entries, and didn't find anywhere that I should not post simple problems, so please forgive me if my challenge sounds less than exciting.

I have a nice DIY power bank case for 18650 li-ion batteries that unfortunately lost it's microUSB connector for charging, it just fell off due to insufficient assembly quality control, I suppose.

I now have other power banks much more efficient and powerful, but this one provides a solution for a need that has recently emerged: controlled charge and discharge of unprotected 18650 batteries and use them permanently as a simple backup power for the ever growing collection of devices with frustratingly small batteries.

Back to the problem at hand, since this is a simple power bank no data wiring is used, and I suspect the normal pinout diagram does not apply.
I uploaded the images of the circuit board, if any of you has suggestions of how to find where to solder +/- wires or test it with a normal voltmeter I would be very thankful. Here are the images (click to enlarge):

This last photo shows where the original microUSB connector was:


Thank you very much for your time.

 

It IS a simple job, but not for beginners.
How much experience do you have using copper braid solder wick?
Have you ever used flux?
What brand and size soldering irons do you have?
Can you get any trashed electron stuff to practice with?

You don't have to answer all of that, but we need to know where you are in order to give you directions to where you want to be.

Easy answer is you are serious about everything electronic and have used an iron for a few months or more. Gets harder and harder to help you do this as YOUR skill level with the tools shrinks.

I suggest you find and purchase the awful, terrible, no good, old solder with the lead. 63/37 perfect or 60/40 if you must. Get liquid type alcohol resin flux(you might never have to buy it ever again)
Get the braid copper solder wick. Get coarse steelwool type pot scrubber and a common sponge. Get a spring piston solder sucker. Get a small pair of quality wire cutters. Small needle nose pliers. XACTO knife and razor blades.

With no power applied anywhere (batteries out), clean up the spot with alcohol and toothbrush
Examine closely for any solder shorting things together and carefully clear with knife.
Check for voltage using a meter. Helps to have a second person when holding two probes on tiny pads.
You'll find the pins are probably grouped and all connected to together for extra current capacity thru the small contacts in the USB port

 

It IS a simple job, but not for beginners.
How much experience do you have using copper braid solder wick?
Have you ever used flux?
What brand and size soldering irons do you have?
Can you get any trashed electron stuff to practice with?

You don't have to answer all of that, but we need to know where you are in order to give you directions to where you want to be.

Easy answer is you are serious about everything electronic and have used an iron for a few months or more. Gets harder and harder to help you do this as YOUR skill level with the tools shrinks.

I suggest you find and purchase the awful, terrible, no good, old solder with the lead. 63/37 perfect or 60/40 if you must. Get liquid type alcohol resin flux(you might never have to buy it ever again)
Get the braid copper solder wick. Get coarse steelwool type pot scrubber and a common sponge. Get a spring piston solder sucker. Get a small pair of quality wire cutters. Small needle nose pliers. XACTO knife and razor blades.

With no power applied anywhere (batteries out), clean up the spot with alcohol and toothbrush
Examine closely for any solder shorting things together and carefully clear with knife.
Check for voltage using a meter. Helps to have a second person when holding two probes on tiny pads.
You'll find the pins are probably grouped and all connected to together for extra current capacity thru the small contacts in the USB port

Dear @Kermit2,
Thank you so much for your reply. I have had a busy week but yesterday, finally, I could resume the project and had a pleasant surprise opening this forum thread.
I wasn't expecting such a detailed message! You definitely sent me on the right path and renewed my curiosity with this project.
Answering to your questions, I do not have any experience using copper braid solder wick, in fact I don't even have it at home. Never had to desolder anything as small and delicate as a PCB. I have flux, and have used with whenever the flux-core solder is not providing good results. About brand and size of solder iron I'm afraid there's nothing I can be proud of, it's a brand less intermediate sized tip iron.
I'm sure I can find some old electronics to start practicing with a braid copper wick.
Anyway I didn't want to wait for that items to get my hands back on it so I started measuring the pins, and found out there is no shorting anywhere but the ground pins (left pin and microUSB port solder points / full sized USB ports and other places). On the other hand, I found out the data pins are probably isolated and the right pin is the positive pin (exactly like the pinout diagram I mentioned earlier). I managed to solder a temporary low amp wire and successfully revive the controlled "Japan SeiKo Li-Battery protection IC" charging function.
I will now try to get my hands on braid solder wick and a thin tip iron, because that positive pin is so small it is almost impossible to get a good work done with with my current set up.
Once again I am very grateful for your reply, and for giving me priceless tips on getting the tools I need to work on these precision projects more often.