820-3437-B loud fan & hot U3900

[Flippers McCoy]

Hey, everybody!

I have an 820-3437-B board that doesn't power up properly. The charging light goes from green to orange, and the fan powers up, then slowly ramps up to 100% speed. I get all S0 rails active at this point (at least 5V and 3V3, anyway). As soon as I plug in the adapter they appear, then a few seconds later they go to 0V for a couple seconds, then come back and stay while the fan spins 100%. While I was measuring, I noticed that U3900 gets very hot, so I tried reflowing it, then removing it and putting it back on. It is possible that I reinstalled it improperly, as I'm still working with a heatgun and tweezers, but I still have the same symptoms after doing that, and it passes a visual inspection and I can poke at it and it doesn't come off.

Does anybody have an idea as to what I should check first?

Thanks!

[SMDFlea]

Re: 820-3437-B loud fan & hot U3900

How did you put U3900 back on ,did you use a stencil.

[Flippers McCoy]

Re: 820-3437-B loud fan & hot U3900

I haven't done BGA work before and almost no clue how to do it properly, so I just blasted the solder pads with my heatgun until they melted and plopped the chip on there and slid it around until it seemed to be in the right place again

[SMDFlea]

Re: 820-3437-B loud fan & hot U3900

Did you say heatgun.... do you mean a hot air station. I don`t think a stencil is available, the balls are 0.25mm according to the 2nd link,you could use a iphone or generic stencil,but its not going to be easy,or buy a new chip, and a hot air station if you don`t have one.

http://advancedreworks.com/forum/arc...hp/t-1558.html

https://www.rossmanngroup.com/boards...3437-no-camera

[Flippers McCoy]

Re: 820-3437-B loud fan & hot U3900

Yep, heat gun, as in one of these (attached). I'm looking into getting a nice Hakko rework station, but that's a little bit off for now :/
Ahh, after reading those I think I understand what you mean. Also, they would suggest that this chip wouldn't stop the computer from turning on, right? I may as well just take it off and call the webcam a lost cause and continue to work on making the computer actually functional again

[SMDFlea]

Re: 820-3437-B loud fan & hot U3900

Even a cheap chinese hot air station is better than a heat gun . TheQuick 861DW is a good station,and cheaper than hakko. My current station is an aoyue 852A+ ,still going strong after 6 years ,and a 858d as a backup.
If you buy a new U3900 it will have solder balls on it.you need to clean up the old solder off the pads , with a decent soldering iron (don`t say you use a firestick..please)

[Flippers McCoy]

Re: 820-3437-B loud fan & hot U3900

I actually have the Quick 861DW on my A list for rework stations, that's the one I'm planning to buy when I round up the money. I got one similar to the aoyue 852A+, but it was absolute garbage. The rework gun was incapable of even melting solder, and if I raised the temperature too high the whole thing would shut off. I'm pretty sure I got a dud.
I actually do have a legit soldering iron! It's an older Hakko, but it is definitely good. I was considering replacing it with a Hakko FM-203, but the Quick is first on my list so I can ditch the heat gun

[Flippers McCoy]

Re: 820-3437-B loud fan & hot U3900

Just for closure, I'm calling it a day on this job. Going to use the board as a donor board, should I need one.

Thanks for the help, SMDFlea, much appreciated

[Stevie2001]

Re: 820-3437-B loud fan & hot U3900

Well as far as i can se nobody here has either knowledge about what type of hot air is good as i dont se the text.

If you ever buy a hotair rework station get the ones with 23L
L stands for liter
Do not buy anything above 23L the lower you can get from 23l its good.

Anything above 23l will take long time to desolder or even toast your board,the heat is not equal and constant temp.

23l is very powerfull provides constant temp and heat it can take any ic or parts of in 3 4 seconds.
It can take intel chips off in 20 seconds or less i have it i know just letting you know what to buy.

[petehall347]

Re: 820-3437-B loud fan & hot U3900

Well as far as i can se nobody here has either knowledge about what type of hot air is good as i dont se the text.

If you ever buy a hotair rework station get the ones with 23L
L stands for liter
Do not buy anything above 23L the lower you can get from 23l its good.

Anything above 23l will take long time to desolder or even toast your board,the heat is not equal and constant temp.

23l is very powerfull provides constant temp and heat it can take any ic or parts of in 3 4 seconds.
It can take intel chips off in 20 seconds or less i have it i know just letting you know what to buy.

just in time as considering one soon . .. heat guns destroy plastic connector surrounds . and get very hot . plus mine are broke anyway . surface mount is hard enough for me when i can see it .