Need Help Repairing Toshiba Satellite C55D-A laptop - Page 1
Forum section: electronics / repair

author: dhodapp
author_rank: Newbie
timestamp: January 07, 2016, 05:12:04 pm
content: Hello everyone, I'm new to this forum so I'm hoping I do this correctly. Recently a family member's toshiba satellite c55d-a stopped charging the battery and could not be powered from the input. The battery powered the laptop fine and it worked fine. The supply seems to be working; outputs its 19V spec and so forth. So I took it apart and began probing around the charging circuit and found some things amiss:First I noticed that USB ports output 3V-ish under load that spike up to 5ish every second.Second the main power bus begins with 19V but at some point ends up looking like MainPowerSupply_2.jpg attached below (basically every second it resets to 5V and then builds up to the 19V only to reset again).Lastly after further probing I found where the 19V turn into the intermittent 5 to 19V. I've attached Board.jpg (that squiggly line is the voltage wave form I'm getting on that power rail) which I have circled where the transition is made. It looks like those two ICs have something to do with it but I cannot find out what they are (mosfets maybe?); they are both the same IC and I labeled their orientation with a red dot. They are labeled: E4 GND 5P0712, which turns up no results for me. Anyone recognize it?The bottom of the two ICs has 19V to gnd on the bottom, the top of the top IC has the strange varying voltage and in between, I'm not sure what is going on (no voltage or signal to ground) but the bottom IC has 15.3V across its bottom and top pins and the top IC having a varying voltage across its top and bottom pins (I cannot give specific details cause I cannot find a good point to reference my oscilloscope probe to and had to use a multimeter.I cannot find a schematic anywhere online for this laptop as toshiba are very guarded with their schematics for some reason and I cannot replace those chips as I do not know what they are or if anything is even wrong with them.So if anyone can help me I would really like to get the laptop working since it still worked with the battery (battery's dead now) and seems to only be a charge circuit problem. Thanks!

author: poot36
author_rank: Frequent Contributor
timestamp: January 08, 2016, 06:08:50 am
content: Try searching for the model number printed on the motherboard not the laptop model for the schematic. If the devices you have circled only have 3 connections to them then they are mosfets. Try and find the chip that controls them and look at its datasheet for a generic implementation of the charging circuit. Check that the mosfets are not shorted (between all three pins) and that the body diode is ok. This will cause the sense resistor to detect an over current situation and shut off the main input mosfets(s) to protect the laptop and power adapter. What does the laptop do if you plug in the adapter but not the battery? Also check for shorted capacitors.

author: Rasz
author_rank: Super Contributor
timestamp: January 08, 2016, 08:24:38 am
content: I am guessing charger circuit is shorted and pulls 19 to ground every time it tries to charge?seeing how you didnt recognize mosfet switches this repair might be beyond your capabilities, not to mention this laptop is pretty crap to begin with and not worth repairingkeep harddrive,throw the rest away, or sell on ebay/craiglist for parts as broken ($20?)

author: amyk
author_rank: Super Contributor
timestamp: January 08, 2016, 12:05:42 pm
content: The C55D-A is apparently an Inventec Durban10AN and I couldn't find a schematic for it either, but looking at the component designators you may have something very similar to Inventec Dakar10F (which there is a schematic for, so get that and take a look). It's not unusual for several laptop models to share much of the circuitry especially for things like power/charging.In this case it seems almost exactly the same down to the designators - U6000 is the controller, a BQ2475, and Q6001 and Q6000 are the charger MOSFETs. Q6010 and Q6011 control AC adapter input.

author: dhodapp
author_rank: Newbie
timestamp: January 10, 2016, 12:54:52 am
content: Okay, first of all thanks for the help, especially for the schematic. From what I can gather the mosfets need replacing but then again its kind of hard to gather anything when it's all in circuit. I try that and see if it fixes the problem. Otherwise the only thing I can think of that's wrong is the charging ic as everything else looks fine.Quote from: Rasz on January 08, 2016, 08:24:38 amYou are probably right... but that hasn't stopped me before.