Li-Ion Charging Board... - Page 1
Forum section: electronics / repair

author: abrasumente
author_rank: Contributor
timestamp: March 08, 2025, 08:40:36 pm
content: Long time listener, first time caller.I have a Bluetooth speaker that refuses to operate unless plugged in. So I tore it apart and determined that there's a problem in the charging board for the li-ion battery pack. At the plug, I have continuity from red to b+ and yellow to its pad (pretty sure this is a sense wire that tells the speaker what the battery charge is), but nothing from black to B-. I also have nothing from another B- pad on the other side of the board to the main B- terminal that goes to black. I see no fried components, carbon tracking, physical damage etc. My knowledge stops here. This speaker wasn't very expensive, but I'd rather fix it than toss it. It also gives me an excuse to get into component level repair.I've found some battery packs online that are close, but none which have the yellow "sense" wire and I figure if its not present the speaker will throw a fit. The pack I have currently is fine physically. Each cell shows close to full charge.Background, I'm an experienced HVAC tech that's tinkered with electronics on and off for 15+ years. I have enough knowledge to be dangerous but enough sense to not get myself hurt or killed, a multimeter, an o-scope, and a soldering iron.Where do I go from here?

author: electronix27
author_rank: Contributor
timestamp: March 09, 2025, 03:13:26 am
content: HiThe battery protection chip, or battery management chip is the 6 pin chip marked 20CB. The other five chips marked 8205A are N Channel Enhancement Mode Power MOSFETs. I have a similarly designed circuit that came from a broken laser pointer. The Lipo is quite small in that circuit so it only uses one 6 pin 8205A chip. Your board has five, eight pin in tandem, most likely for the greater load.The link for 8205Ahttps://datasheet4u.com/datasheet-pdf/HOTTECH/8205A/pdf.php?id=1351448and 20CBhttps://www.hycontek.com/wp-content/uploads/DS-HY2120_EN.pdfSorry, this Mac seems to have issues getting content onto page properly, should be good now. Hope this of use to you.Russell

author: abrasumente
author_rank: Contributor
timestamp: March 09, 2025, 01:05:46 pm
content: Thanks electronix27, I was unsure of what the 20CB component was, so appreciate you doing the leg work on that!I have time to piddle today, so will report my findings later.

author: abrasumente
author_rank: Contributor
timestamp: March 16, 2025, 02:52:04 pm
content: So I've determined there is a break in the board trace going back to the B- pad at the black wire. Near as I can tell, all the other components on the board are OK. I have not been successful in finding a proper replacement battery pack with the third yellow wire.I'm giving some thought to making this my first electronics project, by duplicating this board and wiring the battery pack to whatever I hack together. There is plenty of room inside the speaker, so maybe doing some type of pcb prototyping board will work instead of using regular breadboard.What gives me pause is actually connecting the pack to this theoretical board- I assume the connections were originally made with a spot welder, and I don't own one of those. I've also dropped quite a bit of coin here lately for testing equipment. Are there other acceptable ways to tie a battery pack to a board?

author: electronix27
author_rank: Contributor
timestamp: March 16, 2025, 05:22:16 pm
content: Here are a few photos of the board I've been testing and making measurements on. Much more condensed and DW01 chip is designed for a single battery as opposed to the 20CB two cell, but same type of design. I have great interest in how this works and if the circuit preformed as specked in the data sheet. I have de-soldered and re-soldered this battery back to the PCB with no issue. Also added some wires for +5 charge rail and for load. The header pins are to complete switch contacts and connect an ammeter. If your batteries are charged, I doubt there is anything wrong with them, the circuit doesn't seem to sense when line voltage is removed to switch back to battery power. If there was a break in the battery minus connection that may be part of the problem. What exactly does the yellow wire connect to on the board (and in batteries). I took apart a battery speaker and the battery pack was nothing more than four 18500 type lithium wired in series that were spot welded together. inside of a plastic type housing. The internet is full of things that I think are misleading. Nothing wrong with spot welding, but I see no reason why you couldn't just solder the tabs back together, I would. Just don't puncture the casing on the lithium cells. Maybe check to see if there are any dry joints on 20CB chip. Might just be picture resolution, but a few didn't look the best.

author: armandine2
author_rank: Frequent Contributor
timestamp: March 16, 2025, 06:45:52 pm
content: ....I have put off inspecting my bluetooth speaker's charge board - too longhttps://www.eevblog.com/forum/repair/rockbox-chunk-not-charging-simple-repair/

author: abrasumente
author_rank: Contributor
timestamp: March 18, 2025, 01:12:47 am
content: The yellow wire goes through R4 (meter says ~10k ohms), the other side of which is jointly tied to C3 (assuming a capacitor) and B- trace. The opposite side of C3 is on B+ trace.I do not have an esr meter. May end up pulling the caps and measuring them that way.

author: electronix27
author_rank: Contributor
timestamp: March 18, 2025, 01:05:18 pm
content: I would put this circuit back together as originally was. Test to see what charge voltage is. Test to see if battery voltage is rising, indicating a charge. Repair the broken trace for B minus, my bet on the problem. You can look at the circuit on the PCB and draw it out, use your meter if necessary to locate connections that are hard to trace visually. Look at the circuit in the PDF, should be very similar to your drawing. Having a basic understanding of how the circuit works will be helpful in finding the issue.

author: abrasumente
author_rank: Contributor
timestamp: April 11, 2025, 06:07:40 pm
content: So I set up my test bench with the charging board wired together the way I believe it came, plugged into the main board, and hooked the speaker up to the main board as well. Success! It played for 20 minutes off battery power.Unfortunately, tragedy struck after I made permanent connections on the battery pack. I had everything reassembled in the speaker enclosure, and as soon as I hooked the battery pack up (last connection to be made before sealing the speaker up), a component on the main board decided it was tired of living and let the magic smoke out in spectacular fashion. Everything was hooked back up exactly as I had in testing, with the exception of also having the AC-DC board plugged up since I was reassembling. Something on the AC-DC board must have been the culprit from the beginning, which I admittedly did not check, and likely shorted a connection in the charging board. When I made my repair, I took care to label the connections on the battery pack, so I know I didn't cross anything.Oh well, ya live and learn. I cannot tell what the component was that fried, and without a schematic I can't repair it at this point.