Samsung S2 (SM-T813) tablet  - Page 1
Forum section: electronics / repair

author: najrao
author_rank: Regular Contributor
timestamp: September 09, 2022, 01:00:53 pm
content: Somewhat hesitatingly, I seek help and advice in restoring my trusty old tablet. I tried to connect an OTG cable and a USB 'pen' drive, which fried the charging chip. Result: the 5600mAh battery would drain a whopping 700mA even with the machine turned off. The battery's BMS saved it an hour later by shutting down. Days later, recovering from the bereavement, I managed to take off the back of the case, and remove the ill-fated battery. It is still good and accepted a 5400mAh monitored charge.By injecting up to 700mA into the battery nodes, I found this charging IC (SM5703A) going hot and about to release the magic smoke. Indeed this was under a metal shielded area, which needed decapping. See pictures. Extensive googling says this chip is a common failure point, but for the life of me -- no data sheet is forthcoming, not even pinout. It is BGA with 30+ pins, none accessible for probing.I cannot remove the board itself from the assembly. This requires removing the display screen.After many unsuccessful attempts with soldering iron and improvised hot air, I finally plumped to dremelling the chip off. A diamond ball tip on a 30 000rpm dentist's drill just took the outer plastic off. So, the desperado in me used a carbide milling cutter in a regular dremel knockoff. The result: surprisingly good and clean . See picture. (One solder pad appears to be missing, but the next is joined to it).Since I cannot hope to solder back a new SM5703A, I propose to lead the battery nodes out of the case (somehow!), and charge using an external charger.With the battery bleeding heavily as it did, the tablet had been seen to be working normally while the charge on the battery lasted. So, all I need to do is to identify the pin number on the BGA array on the board which is the Vcc for the works.But alas, it appears there was a mosfet switch in the now defunct chip, which turned it on by logic (as from the start button). I could substitute this switch by hardware, but for the life of me I seem unable to identify the needed node.I understand this maverick approach may be null and void due to yet unseen complications. I have nothing to lose, and may yet gain access to the data horde in this tablet.Please advise me. Thank you.

author: fzabkar
author_rank: Super Contributor
timestamp: September 10, 2022, 01:27:57 am
content: It appears that this PMIC chip is a lot more complicated than you think.https://uploads.tapatalk-cdn.com/files-1630/SM-T377A_Tshoo_7.pdfhttps://www.tamiraat.com/repository/other/1398/10/07/rhdmp0o4.nms.pdfhttps://www.tamiraat.com/repository/other/1398/10/07/eszmapzf.dpr.pdfhttps://dl-manual.com/doc/manual-de-servicio-6vjgky21wnve

author: najrao
author_rank: Regular Contributor
timestamp: September 11, 2022, 09:44:31 am
content: Thank you, fzabkar. You put me wise: these are indeed deep waters. The only possibility seems to be to try and replace the chip, and I just don't have the skills and tools needed. Getting it done at a professional repair facility is unlikely to be cost effective. And there is no proof that it will work thereafter.Identifying the Vcc node (which must be one of the chip's pins) is not straightforward. Injecting Icc at up to 4.0V randomly did not start up, but may be more conditions must be satisfied to enable. Your thoughts please.

author: fzabkar
author_rank: Super Contributor
timestamp: September 11, 2022, 05:08:27 pm
content: I'm guessing that the PMIC needs to communicate with the main controller, so even if you were to power up everything, the controller may sense that something is wrong and refuse to continue. But that's just a wild guess.