A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

[mon2]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

it suggests that the short is further downstream?

Yes. With these 2 resistors OFF the logic board, power up again.

Measure the voltage to ground at C6912, pin #1.

What is the voltage? If it is ~3v3, the regulator @ U6903 is working fine and does not need to be replaced.

Next, remove all power -> dial up your power supply to 1 volt (NOT higher for safety - in case the power rail is shorting to the CPU rail through a leaky mosfet) and 2A-5A current.

With no power to the logic board but using only this external power supply, attach the RED power supply probe onto R6934 or R6935, pin #1 (either one is ok). BLACK power supply probe to ground (shield is ok).

The power supply current consumption should spike due to the ultra low resistance on this rail.

Who is heating up using this process? You can pour IPA onto the board / area you suspect is causing this short. The IPA will mist up and evaporate quickly from the heat. With some luck, it will be a defective capacitor which is quite common. The longer you keep the probes attached, the hotter the shorted component will get. Hope it is not the CPU (do monitor the CPU without a heatsink). Often the caps are tantalum style and they split / crack open under this event. Tantalum caps are just crap and they short circuit when they die over time. Once you home in on the shorted part, remove that part off the board with flux and low air pressure, so the parts do not go flying (without a license).

Then allow the board to cool down and measure the resistance to ground again for the same short condition.

Post your updates and measurements.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Power supply came today, just couldn't justify pulling the trigger on a thermal camera... will update later today, thanks!

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

I don't understand it, but voltage to ground of C6912 @ pin 1 is 12.3 V steady. Same as the input voltage to the chip measured @ C6909...

So the chip is acting as a wire now? Furthermore, according to the TPS62180 spec sheet,the max allowable output is 7V.

So I guess we have two problems now, short after circuit and perhaps this chip is still faulty?

[mon2]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Whoa! See attached.

You are measuring ~12v3 to ground @ C6912, pin #1 ??

That is very dangerous but believe that the 2 x downstream 0 ohm resistors are REMOVED off the board ? (R6934 & R6935 are OFF the board).

DO NOT connect these resistors till this power rail returns to within range.

Summary - Vout = Vin ???

Remove all power and do confirm that the feedback resistors are matching the resistance shown in the schematic.

The FB resistors are R6912, R6913, R6910, R6911.

That is, this rail must be ~3v3 else there will be other damage to the board.

short after circuit and perhaps this chip is still faulty?

Yes. It appears to be so.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Correct, resistors R6934/35 are still off and I won't reconnect. Thanks for the heads up on that.

See attached pictures of my readings/locations.

Testing resistors now.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

R6910: Reading 450 kOhm, Schematic 360 kOhm
R6911: Reading 71 kOhm, Schematic 115 kOhm
R6912: Reading 10 Ohm, Schematic 10 Ohm
R6913: Reading 0.04 Ohm, Schematic 0 Ohm

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

What your thoughts on the readings? Does this mean a trace is wrecked or something?

[mon2]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Remove each of these resistors but do so one at a time and then measure when the part is on your work table. Allow it to cool before measuring.

Does the part value measure to the schematic value?

If yes, place it back and remove the next resistor to test.

It is possible that the resistor values are showing a different value while in circuit vs. off the logic board.

Confirm the feedback resistor values and update this thread.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Wow, that was hard! Those resistors are so small - I can't believe I didn't lose any (pic attached).

In any-case, here are the updated readings:

R6910: 360 kOhm
R6911: 115 kOhm
R6912: 10.4 Ohm
R6913: 0 Ohm/OL

The resistors are all to spec, so is it a chip issue still?

[mon2]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Replace U6903 and measure again with the downstream resistors still OFF the logic board.

This power rail must be within spec to match the schematic values.

[reformatt]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

I'd be looking at the pads for this IC. Looked torn/damaged to me in the original posts.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Hi all, sorry for the delay, I was away on work last week, but back now

@reformatt, can you please point out the pads that look particularly poor. Do you have any recommendations on how I can clean this up further, or test for the broken pads?

[reformatt]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

In post #8, your first and second pics didn't look good. Maybe its the way the solder balls reflect the light, but would certainly bear closer examination. Doesn't look symetrical.

Just use the boardview to check for connectivity to other parts, and of course, check for shorts etc. If you have lifted or broken pads, you'll need to review whether they are needed or redundant. If needed, you need to run jumpers, which requires some patience to fit correctly with UV mask etc.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Ok. Correct me if I am wrong, but the only way I can have 12 V both in and out of this chip is if there is bridging of the balls, no?

Also, if a pad is torn off, wouldn't that mean that the connection would stop the current from moving through and thus no reading on the exit?

[reformatt]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Top row of pads is for Vin1/Vin2. The 2nd pad from left, 2nd row looks in the 2nd pic like it is lifted. This could result in a bridge between Vin1 and SW2 once the chip is placed on, hence you'd get 12V on the output. When we place a BGA on, we rely on surface tension of the solder to the pads to pull it into place. If the pads have lifted and moved, this could result in shorts for sure.

Take off the IC, and flatten the pads with wick, clean up, and look again under a scope. You do this a short piece of wick and hot air/flux. Lightly scrape across the pads while applying hot air to remove excess solder. Using an iron with wick is risky as it's very easy to pull a pad if you aren't using the right tip or a shitty iron.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Thanks for the suggestion on wicking - I don't have a hakko, so the hint was welcome.

I have removed the chip and added pictures of each step (i.e. right after removal with flux on it, after I cleaned that, and then again after wicking). I also attached a picture of the chip bottom.

Let me know your thoughts.

Also, re-orderd a couple more U6903

[reformatt]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Right, looks much better than your original pics and pads look fine. You should just meter the pads out to other parts on the board just to make sure there are no hidden breaks at the pads themselves. Use the boardview for that.

When you get the new IC, pre-heat the board with hot air. Once you are close to melting temp, put a small bit of flux down and place the IC on roughly in the right spot. Apply a bit of heat again so that it bonds slightly. Then let go with your tweezers, and heat till you see the chip move into place. Give it a nudge with tweezers and it should pull back into place. Then you should be good to go.

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Thats good to hear, thanks!

I will follow those instructions and update once the part comes in (usually 2 days). Fingers crossed it works this time.

In the mean time, it appears that I have lost C6910, C6901 and C6909 during the cleaning. They appear to be non-critical based on the schematic, what are your thoughts?

[Stiffmesiter]

Re: A2159 - 820-01598 - Stuck at 5V and am a beginner looking to learn

Well, I put it back on, but don't think I did it very well. Sadly, I am at my peak with this machine/project and must move on. Thanks again for everyones help, I have learned ALOT!

I would however still like to get this laptop fixed, if possible. So if anyone can recommend a good shop - preferably in Canada - that I can ship to, it would be appreciated.