Will replacing battery controller IC fix laptop? - Page 1
Forum section: electronics / beginners

author: skillz21
author_rank: Frequent Contributor
timestamp: May 19, 2018, 11:53:09 am
content: My Acer R3 laptop broke last year. I had a look at it today, I had already torn down the battery and repurposed it, but I still had the protection circuitry. I cut off the wires connecting the battery and motherboard and instead connected a 15v DC power supply to the positive and negative terminals. When I connected it, the motherboard drew over 5 amps from the supply, and the voltage dropped to 2 or so volts. Something was obviously broken. (The laptop broke for some unknown reason, when I tore open the battery, the protection circuitry had already kicked in, probably because of the short)I don't have a thermal camera, so I looked on the motherboard and found an IC near some inductors. I googled the part number, (the markings on it said: BQ 737 - TI 56I - AQ8T (the hyphens represent a new line)). After looking around, I discovered that this was a battery charge controller (Success!). As I said earlier, I don't have a thermal camera, so I connected the power supply once again, and placed my finger on top of the IC. Sure enough, after a few seconds, the IC heated up. (I got the right chip on the first try, I'm not sure why it took me literally a whole year to try this)Here's my question, will replacing this IC fix the PC? The initial problem was, this laptop randomly just stopped booting after a shutdown, the charging LEDs wouldn't light up when I connected the power adapter. I found this IC on eBay, but the only problem is, (here'san example) I didn't find an IC that matches the original IC exactly, the ones on eBay say: BQ 737 - TI 25I - ACD8. I'm not sure whether replacing the original chip with this one would work... I'd appreciate some advice on what to do from here.Thanks

author: HecticZA
author_rank: Contributor
timestamp: May 19, 2018, 01:19:16 pm
content: Quote from: skillz21 on May 19, 2018, 11:53:09 amIs the short gone whithout the IC?If not, you will have to troubleshoot a bit further.Sent from my SM-N950F using Tapatalk

author: skillz21
author_rank: Frequent Contributor
timestamp: May 19, 2018, 01:43:08 pm
content: Quote from: HecticZA on May 19, 2018, 01:19:16 pmHow exactly do I test this? Do I need to desolder the IC? (I mean, I would assume that this IC is the problem, since it's the one that heats up... Then again, my knowledge of electronics isn't that good, so I'm not sure) If this IC was the problem, would those ones on eBay even work as a replacement? since they don't have exactly the same markings?

author: nuno
author_rank: Frequent Contributor
timestamp: May 19, 2018, 02:00:51 pm
content: You can find a few videos on the subject, for example

author: Spudlicious
author_rank: Newbie
timestamp: May 19, 2018, 03:07:57 pm
content: My repair experience would suggest that a hot IC is probably a good one. They die cold just like us.

author: skillz21
author_rank: Frequent Contributor
timestamp: May 20, 2018, 02:28:51 am
content: Quote from: Spudlicious on May 19, 2018, 03:07:57 pmNot sure whether you are serious or not...If the battery is shorted, then isn't the IC that heats up when the battery is connected a good guess as to what went wrong? Also, it's this IC that controls the battery... If this IC is fine, then what else could have gone wrong? The problem with this laptop was that it didn't start up, and the charging LED wouldn't light up... I have a theory, could the laptop just received a surge from the external power adaptor? This then shorted something inside that IC... Could this have been what happened?Also, what about a replacement IC? Would that one I've linked to on eBay work?Thanks for all the help guysSent from my SM-G900I using Tapatalk

author: switch998
author_rank: Contributor
timestamp: May 20, 2018, 03:32:22 am
content: Quote from: Spudlicious on May 19, 2018, 03:07:57 pmThat's right, I remember when my school teachers told us that when lightning strikes the ground, it produces a remarkable cooling effect. Have you ever seen a tree get struck by lightning? Instantly frozen.So, with 5A of current being shorted to ground, you're right that OP should be looking for a cold IC, not a hot one.Quote from: skillz21 on May 20, 2018, 02:28:51 amIf that IC is running too hot to touch, then it's probably bad. Remove the IC and check if the short is gone. I'd order a new one and replace it either way. And FYI - the rest of the part markings are the lot / date codes. BQ737 is the part you need, the rest of the markings shouldn't matter.Before you do that, I would check for shorted FETs too. When I used to work on laptops, it was a very common problem for the input mosfets to fail dead short, you really only need a multimeter to accomplish this test.

author: paulhm81
author_rank: Regular Contributor
timestamp: May 20, 2018, 04:52:01 am
content: Don't try to power the board without the ic unless you desolder the mosfets that are connected to it or you might do additional damage to the board. Without the ic the transistors might be fully open and fry components downstream. Check for shorts in the area on the transistors, smd capacitors, tantulum capacitors, diodes....

author: skillz21
author_rank: Frequent Contributor
timestamp: May 20, 2018, 05:10:58 am
content: Quote from: switch998 on May 20, 2018, 03:32:22 amOk, I will test for the shorts, but for the chip itself, should I provide power to it for a while longer to see if it gets hot enough to burn my hand? Also thanks for the advice with the IC on eBay.

author: skillz21
author_rank: Frequent Contributor
timestamp: May 20, 2018, 09:07:20 am
content: I tested the MOSFETs around the chip... everything seems to be working fine... Should I just go ahead and buy the IC? See if it works or not?

author: skillz21
author_rank: Frequent Contributor
timestamp: May 21, 2018, 11:29:27 am
content: Also, what was that liquid the guy in that video poured on the components at 22:00?

author: HecticZA
author_rank: Contributor
timestamp: May 21, 2018, 11:51:49 am
content: Quote from: skillz21 on May 21, 2018, 11:29:27 amHe normally uses lighter fuel, something like Zippo fluid.Most people use freeze spray in a can or you can grt a similar effect with air and spraying it upside down and blowing on it.A popular option is Isopropyl used in the same way as with the lighter fluid in that video.Sent from my SM-N950F using Tapatalk

author: skillz21
author_rank: Frequent Contributor
timestamp: May 21, 2018, 11:58:37 am
content: K cool thanks for the info.