MacBook Pro 2019 A1989 - Damaged right fan control

[Transient77]

I have a damaged MacBook Pro 2019 A1989 (EMC 3358) with a damaged right fan control (stuck on maximum). It was damaged by the repair shop conducting a warranty replacement of the touch bar / top case. I was compensated for the damage by the warranty company, but I was hoping to repair it myself (hobbyist).

On investigation, I learned that by design the fan will run at maximum RPM when the PWM control signal is missing.

That led to me to review the logic board schematic and I found the location of the PWM control signals. I took a photo of this area of the logic board and have attached them to this post.

As you can see, the right fan PWM circuit is missing the MOSFET. This part is very tiny, 1.10 x 0.70 mm in size and I assume was knocked off by someone during the touch bar repair.

I know it's probably a long shot, but does anyone have any experience fixing something like this? I had some ideas:

• disconnect the right fan (machine runs hot and slow/throttled)
• bridge the output from left fan PWM to right fan PWM, using the nearby test pads, thereby tying the two together
• attempt to install a replacement MOSFET (DMN32D2LFB4), using a heatgun, potentially destroying the board due to lack of skill / correct tools
• give up, sell for parts

 

[andrewv69]

Fixing that requires microsoldering, which is pretty difficult if you've never done it before. Judging by your post it seems you're not too confident in your soldering tools/skills, so I'd say send it off to a pro, if it's even worth fixing. Get a quote first of course, and be aware if they were careless enough to knock off a cap, there might be other damage too. Rossmann repair or other place that does microsoldering would be able to do that no problem, should be a pretty easy repair.

 

[pacmania1982]

You might be OK with some solder paste and a hot air station.

 

[Transient77]

Thank you both for the advice.

After looking into the cost of a cheap hot air station, I decided to order one and will give it a go when the parts arrive.

It's true, I have no experience soldering something like this, but I already have a digital microscope and I am confident that I can accurately place the part. I think with the correct tool (hot air station) I can do it as there's fortunately room to work in that area.

Worst case, I will learn a bit more.

I did have a look over the board and I couldn't find anything else missing, although it's probably easy to miss.

 

[Transient77]

Just a quick update, in case it helps anyone else in the future.

I'm still waiting on the replacement MOSFET and I am starting to think it's been lost in the mail. In the meantime, I've learned a lot about how these fans work.

Today, I decided to try installing a jumper wire between the two PWM test points (left and right fan PWM). I used the test points since they're easier to work with. The idea is that it'll tie the two fan speeds together and my MacBook won't sound like a jet engine.

I'm happy to report this works and it can be accomplished without any specialized equipment; just a standard soldering iron will do.

The downside is you can't independently control the fans, but it's better than having no control. Maybe a fan control software would help.

I'll post a final update whenever I receive and install the MOSFET.

 

[Transient77]

Sadly, replacing the missing MOSFET did not fix the problem. The only explanation I have is maybe the pads are damaged, but it's impossible to trace it back to the SMC. Or maybe the SMC itself isn't sending the PWM signal, but I'm not sure why that would be.

I've restored the previous workaround, which actually has been working well anyway.