Samsung NP700Z5C - completely dead (but FIXED now!)

I posted in some other threads when I first had this issue and got some great feedback and help. Said I would post more details in a dedicated thread so here it is:

The backstory:
So, my son came over with his laptop having problems. Had been booting slowly (which seems to be related to the iSSD they use as a cache). I had picked him up a SSD to replace the hard drive and since we had to open it up for that I thought it would be a good time to check for anything else (clogged fans, battery capacity, loose connections, etc). Also, figured when we swap drives we'd disable or bypass the iSSD too. We opened it up, cleaned the fans and checked the battery but then it wouldn't boot at all. Doesn't charge, no lights, nothing. Battery is good, incoming P.S. is good and voltages from both showed up on the MB. I didn't have a schematic or board layout but by poking around was able to verify the SMD fuses were all good. Something else was going on but I couldn't figure it out.

I ran across a nearly identical machine for sale, so I picked it up thinking he could just swap his HD in and be back in business. When we got the 'new' machine, we booted it up and checked it out and everything worked OK. When we popped both machines open to swap harddrives, I thought about doing a little troubleshooting...perhaps we could get them both working! Lets compare voltages and swap a few parts! We first put the 'new' battery in the 'old' machine but it didn't boot up. We put the 'old' battery in the new machine but it didn't boot up either. Hmmmm. We put the 'new' battery in the 'new' machine and now it doesn't boot up either!!! ARRRGH! Now we had TWO machines with the exact same symptoms.... looking COMPLETELY dead but both have a good battery and a good PS feeding the MB.

Took me a few weeks to track down a service manual. I thought I perhaps did something wrong opening them up but reading the service manual showed that I did everything "by the book". I have never broken something like this just by disassembly (other than the occasional plastic clip or snap ).

Took another week to track down a schematic and board layout. I suspected U529 (BQ24735RGRR) was the issue, as it seems to control the charging and enabling the P.S. input and battery input lines. Everything seemed to look good there though so it seemed like "something" wasn't telling it to turn on (via SMDATA??).

After many tests, I think I have tracked the core issue down to a problem on the 3.3v_MICOM circuit... as there is no 3.3VDC here when there should be (all the time). This is supplied by U520 (TPS51125RGER). I can also feel U520 getting really hot too, so something must be shorted. U520 also supplies 5.0V_STB and that seems OK. Took a while to find everything that might be a possibility on the 3.3V line and I was hoping it would be something easy like a cap or diode shorted to ground. No luck there. What I did find is when I put an external P.S. with 3v to that 3.3v_MICOM circuit, that U516 (MEC1310-NU) gets HOT quick. U516 would also be the chip that supplies SMDATA back to U529, the charge controller.






So I ordered a couple MEC1310's so I can practice replacing them and hope it's the issue.

 

Update... FIXED!!! (well, almost!).

I picked up a rework station (hot air and iron, as my irons tip was about 10x too big) and went to work. I have never worked on SMD board before and didn't have anything to practice with, so I got to work. (rethinking that, I did have some older graphics cards I could have sacrificed, and should have used them for practice!!)

To see the detail on the board, I'm using a combination of two magnifying glasses... one lit and one handheld (see pic). Not ideal in any sense of the world, but workable.



I had to remove an MEC1310NU - 128 pins, so I used heat. After reading many posts and viewing a few youtubes, I preheated to board up to about 100c and then put some heat on the 1310 while gently pulling up with tweezers. Unfortunately, I was pulling just a bit to hard or had the heat on a bit too long because about 7 traces came up with the chip when it finally broke free from the board!! ARRGH!

I got the new 1310 in place and was able to get the 121 good pads soldered down. I used a pin tip and did each one individually. Had some solder bridging a few times but cleaned that up as I went.

I took some wire-wrap that I had laying around to do the jumpers for the missing pads. Took quite a while to find suitable places to tie the other ends in, but I found them.

Powered up the board and I still had a non-working board and short-to-ground on the 3.3v MICOM line. ARRRGH!!

Reviewing each pin, I found two places where there were still solder bridges, so I worked to remove them and tried again.

SUCCESS!! I now had a "AC POWER" LED lighting up!! Put the whole laptop together and was able to get to the BIOS setup screen.

BUT - when I got the BIOS to setup and it went to boot to Windows, the PC would shutdown. I believe that the surge of current when the screen lights up is too much and not buffered by the battery. When I had the laptop apart, I tried to manually charge the battery with a variable PS. I must have done something to the circuit inside the battery pack because it won't 'reactivate' when connected to the laptop and powered up. Might be buying a new battery to resolve that if I can't figure it out.

 

Hello,
Do you have the schematics for NP700Z5C?
Can you share?
Thanks