Laptop won't power on/ 1225C IC extremely HOT - Page 1
Forum section: electronics / repair

author: UnkleBidii
author_rank: Contributor
timestamp: June 04, 2017, 12:24:55 am
content: Hey dudes!So my Toshiba finally gave way last night. Won't power in due to a short I may or may not have created. It was working before I decided to test some older batteries of the same model to see if they would charge or what.. This laptop has been a problem the last 2 years.. It seems to be killing batteries. I've gone through 4 batteries that work for awhile before they start only discharging to a point then shutting down with no warning on percentage levels. Some at 50%, 35%, etc. This is with the numerous batteries. The latest one I have would discharge to about 40-50% before shutting down no warning. I wanted to troubleshoot what was going on for awhile but I have no schematic. It's a Toshiba Satellite p55t-a5118. It's only 3 years old. Anyway, it's an internal battery which then plugged older batteries into to see of they would charge... Maybe I could use those for other projects(maybe the problem is my laptop). Well, they didn't seem to charge so I plugged battery that's installed back in, put the cover back on, and it wouldn't power up.. On battery or cord.. Another tear down revealed a hot spot on the MBoard.. So I unplugged everything. Further teardown revealed the hot chip to be a 1225C chip on the bottom side of the MB. This heats up when either the battery or cord is connected. This laptop has seem to be more of an issue pit but it's my only laptop I have at the moment. Any advice to try and save it? Only option I have is to buy another MB at $$$ or try to find the short, then remove components until the short is removed.. I've troubleshot pcbs in the past for work but still considered myself novice.Thanks for any input buds!

author: orbanp
author_rank: Regular Contributor
timestamp: June 04, 2017, 11:32:55 pm
content: That chip is a 5V and 3.3V step-down regulator, here is the datasheet:http://www.ti.com/lit/ds/symlink/tps51225.pdfThere are snippets of application circuits in the datasheet that could help you debugging the laptop.It is also cheap and available at DigiKey:https://www.digikey.com/product-detail/en/TPS51225CRUKR/296-39402-1-ND/5143353Does the laptop run? Are the 5V and 3.3V present?If so then it is possible that the chip itself is faulty.You could take a shot at replacing it, if you have the technology to do re-work with such smd chips.Good luck, Peter

author: tooki
author_rank: Super Contributor
timestamp: June 05, 2017, 03:55:55 am
content: You think so? I'd sooner suspect that the regulator chip is hot not because it has failed, but because somethingelsehas failed and is drawing far too much current (e.g. failed to a short or near-short).

author: orbanp
author_rank: Regular Contributor
timestamp: June 06, 2017, 07:17:51 pm
content: Hi tooki,With the datasheet and a scope I would check if the signals on the pins correspond to what is expected.That should give you a clue what might be wrong.If the laptop is still running then probably the 5V and 3.3V are there (do check it!), the FETs are probably operational.If any of the gates of the FETs is overloading the output of the control chip and that overheats the chip, a measurement with a scope of the gate signals should show that!So do measure!Good luck, Peter

author: tooki
author_rank: Super Contributor
timestamp: June 06, 2017, 07:39:47 pm
content: I assume your reply is intended for the original poster, not me.

author: orbanp
author_rank: Regular Contributor
timestamp: June 07, 2017, 11:06:36 am
content: Quote from: tooki on June 06, 2017, 07:39:47 pmCorrect, I guess I was not paying attention to the poster's name.Just to clarify a bit further, the load currents do not go through that chip, the chip just controls the FETs.A short on the output voltages might not necessarily overheat the chip.Peter

author: UnkleBidii
author_rank: Contributor
timestamp: June 08, 2017, 08:39:25 am
content: No, laptop doesn't power on.. When the wall adapter or battery is connected, that area of the board is hot. I have not yet check the signals/voltages on the chip itself. I am not familiar with the step down iC and how it controls FETs...

author: UnkleBidii
author_rank: Contributor
timestamp: June 08, 2017, 08:42:42 am
content: I suspect that too.. Which is why I'll more than likely have to purchase a new board rather than play the replacement game with no schematic or readily available parts. I would have to purchase a heat gun to remove it... It's a good laptop and I'm not in a position to grab another any time soon..