Reparing a laptop, please help ID an IC

[instanoodles]

I am working my way through fixing a laptop I got from a friend and I think I narrowed in on the problem. There is 0v on the voltage rail for the ram, I scoped the power mosfet's gate pin and there is nothing. I traced it back to the little IC in the picture, added some white paint and wiped it off to make it easier to read. I have searched and searched but either cant find anything or I have found it but don't recognize it as what I need. The closest I have come is this part, http://www.digikey.ca/product-detail/en/TPS51601ADRBR/296-30534-6-ND/3451688 but I'm not sure. I was thinking it might be a TI part because in the middle line on the ic I think there is "TI" engraved but its very hard to make out. Any help would be appreciated, it would be nice if I could get this thing working again.

I believe the writing on the chip is:
601A
TI
33ZG

[vgamesx2]

If its a TI chip then its pretty obsolete because it isn't listed on their site if you search for it... I'd probably say you're best bet would be to find a replacement motherboard.

[ovnr]

Seems plausible. See if you get continuity between the gate and the corresponding pins; if so, I'd probably take a chance on replacing it.

You might want to probe the PWM in pin on that chip first - the failure may be elsewhere.

[amyk]

TPS51601A looks right. That's what http://www.ti.com/general/docs/partmarking/partmarkinghome.jsp says, anyway.

[poot36]

Is the IC getting hot when the laptop is trying to run?  If yes then the mosfet has shorted and killed the chip.  If no check that the output of the mosfet is not shorted to ground and the protection circuit is not activating and disabling the gate output.

[instanoodles]

TPS51601A looks right. That's what http://www.ti.com/general/docs/partmarking/partmarkinghome.jsp says, anyway.

That's great, I didn't know you could look up their part markings like that thanks!

Is the IC getting hot when the laptop is trying to run?  If yes then the mosfet has shorted and killed the chip.  If no check that the output of the mosfet is not shorted to ground and the protection circuit is not activating and disabling the gate output.

That IC isn't getting hot while it is powered up but since amyk has helped me identify the chip I can now check its function and go form there. I will check to make sure there is no ground short on the mosfet output. thanks.

[Rasz]

laptop model?
have you measured before the mosfet? checked for shorts?

[instanoodles]

laptop model?
have you measured before the mosfet? checked for shorts?

Its a Toshiba C55-A5285 laptop. I have checked before the mosfet's and there is the full 19v from the laptop power supply. It appears to be the proper voltage after tracing it back to the DC jack. I also checked for shorts and don't believe I found any, measuring to ground only reads a few ohms. I thought it was suspect but after comparing it to other voltage rails it appears to be a normal value. I ended up tracing the PWM signal back to this tps51219 step down voltage regulator http://www.ti.com/product/tps51219. The pwm signal voltage that the TPS51601A is getting is correct and other voltage rails that the tps51219 controls are functioning properly. Im inclined to think that the TPS51601A is toast but I would consider myself a newbie when it comes to electronics repair. I have attached some pictures of the pcb if anyone is interested in giving me a hand in this.

Thanks

[poot36]

Check the TPS51601A for all the correct signals coming into it as well as out of it.  In the functional block diagram (Link: http://www.ti.com/general/docs/datasheetdiagram.tsp?genericPartNumber=TPS51601A&diagramId=SLUSAP3) it shows external mosfet's.  Have you tested both of them as well?  Also look for a current sense resistor that may be bad.

[amyk]

Is there a Compal part# on the board (of the form LA-xxxx)? That could help in locating a schematic.

[Rasz]

c855 has almost identical mb
http://www.aliexpress.com/item-img/Original-V000275560-For-Toshiba-Satellite-C855-Motherboard-HM77-integrated-DK10F-6050A2541801-MB-A02-100-fully-tested/2044913057.html

diagram:
http://kythuatphancung.vn/download/inventec-luxor10fg-laptop-schematics.html?dl

edit:

might also be http://kythuatphancung.vn/uploads/download/56e92_Satellite_C650-655-D_-_Inventec_Manaus_10R.pdf

even if the mobo is different inventek reuses same power sections, this one has a nice power sequence block diagram