MacBook Pro 15" A1707 820-00281 repair

[jma46]

Hi I am currently trying to repair a A1707 0820 00281 logic board, PPBUS_G3H gives a negative voltage reading of around -.5v but checking the rail for shorts, seems fine. In the past in this same scenario if I had a negative voltage I would expect to find a short. This is a liquid damaged board and is only drawing .01-2 amps and 5v. Could the short be in between the board layers?

Thanks JMA

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

Remove the fuse(s) on the ppbus_g3h rail.

Then test again to see the voltage is the correct range.

What is the voltage of the USB-C power into the logic board?

Is it 20v or is it lower? Normal is 20v.

[jma46]

Re: MacBook Pro 15" A1707 820-00281 repair

Hi Mon2 removed the fuse pubs_g3h USB-s is 5.03v darling .01-2 amps

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

5 volts means the logic board is using the default output voltage from the power adapter. After some handshakes using the CCx pins on the ACE controllers, the board should kick into 20v mode.

See the article on the net by @Piernov and gang on how 20v is selected for the gory details but start with carefully measuring the LDO regulator rails of each ACE controller. Summary is that there is a fault in one or more of the USB-C ace controller. Each one must be functional to dial up to 20v.

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

https://logi.wiki/index.php/CD3215_Bootup_Sequence

[jma46]

Re: MacBook Pro 15" A1707 820-00281 repair

Im fairly new to all this but picking up odd things as I go, this board in particular, I seem to be getting negative voltage readings off some of the ground points, does that mean I am wasting my time with this board? Thanks for your reply and the link, I will look and try to understand

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

As far as I know, there are no negative rails onboard. If the meter is working correctly and calibrated to the manufacturer's specs, you should not see negative voltages. Are the values small or large for the measurements of the negative scale? Perhaps a no care. You can check the same test points with another meter to be sure.

For the main power rail -> your external power adapter is the feed for the power path -> starts @ 5 volts till the CD321x controllers (CD3215 on your board) handshake and then select 20V power delivery contract. Either way, the 5v or 20v are fed into the ISL buck / boost regulator. If 5v is the INPUT; then the regulator will BOOST to ~12-13v. If the input is 20V as the INPUT; then the same regulator will BUCK the voltage to the lower range (same as above). No negative voltages here.

At this time, since you have only 5 volts being selected (actually is the default on voltage from the adapter) -> need to confirm the CD3215 devices are working. One bad CD3215 can halt the 20V selection process. The above linked article outlines the steps required to reach the 20v power delivery contract. The first step is to confirm that each LDO pin on each CD3215 is able to supply the proper voltage.

The LDO is a linear regulator that will take in the 5 volts and lower it to the voltage on the pin as shown in the schematic. After this confirmation, move the power head to another CD3215, etc. and test again.

[jma46]

Re: MacBook Pro 15" A1707 820-00281 repair

Hi Mon2 I have been flipping between a faulty A 1708 and the A1707 both with similar problems, the A1708 has PPBUS_G3H and P3V3_G3H and no shorts I could find and was not booting. After reballing several CD3125's and no success I went back to the A1707 looking through the links you supplied and the LDO.s required etc. After removing and reballing some more CD3125's from a diner board the voltage shot up from 5-13-20v! and realised it was booting! I have put back in the case and also got an image although it may be flexgate, I had made some good progress which I will look at further when I get a minute. There are some components missing from the board which I do not know what it is, can anyone tell me what the R3540 is on the schematic, the only info it shows is - 0.002 1% 1/2W MF 0306. A google search does not help identify what it is? thanks for the help Mon2 I really appreciate the help

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

That is really good news. The resistor is a 2 milli-ohm current sense resistor and the smd package 0306 size.

Best to search on 0306 smd size and then check if the value is available. Will do the same after my daily dosage of Netflix - Money Heist. My latest addiction.

[jma46]

Re: MacBook Pro 15" A1707 820-00281 repair

Still no luck with defining the part, I have Flexbv but limited info on the schematic I have

[mon2]

Re: MacBook Pro 15" A1707 820-00281 repair

https://www.digikey.ca/en/products/d...F-T50/16735421

[jma46]

Re: MacBook Pro 15" A1707 820-00281 repair

Thanks Mon2, that's brilliant Ill get some ordered, I have tried all sorts of searches but don't fully understand what the part is, but glad you do!