#1 Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on
by valieromarco • 26 December 2025, 03:03
Forum rules: Click here to view the forum rules
- Topic title should contain: the device's manufacturer, full model and the brief description of problem.
- Topic message should contain: the PCB marking code (required in case of hardware repairs), an extended description of problem, things you have checked/replaced/measured, your conclusions and the question. If you are not able to find the PCB marking code, please read THIS TOPIC. If you still cannot locate the PCB markings, please upload a clean, both-side photos of the mainboard - it is required to remove any films, modules or brackets possibly covering these markings.
- Before posting a new topic please read all topics in TRAININGS subforum and make a preliminary diagnostic based on the content of those trainings.
- Uploading of any complete schematics, BIOS / firmware files or any other kind of documentation, or linking to 3rd party websites with such files, is STRICTLY PROHIBITED. You can only upload the small portion of documentation or, link to BIOS file on UNVERIFIED BIOS FILES subforum, which simplifies the diagnostics/repair. You are not allowed to upload more then one complete page of instruction/schematic per single topic. The file you upload must not contain any watermarks, "confidential" markings, links or email addresses and cannot be password-protected.
- It is only permitted to describe one faulty device per single topic - you should always open a new topic for each subsequent device.
- Requesting of the full schematics, BoardView files, BIOS files or any other kind of documentation is NOT ALLOWED in this subforum. If you need to ask for any of these, you should open a new topic in DOCUMENTATION/BIOS REQUEST subforum.
Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on
by Google Adsense [BOT] • 26 December 2025, 03:03
#2 Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on
by Vogelek23 • 26 December 2025, 05:31
ELVIKOM LAB Ltd - Apple Repairs & PCB Design - Free Quotes! https://www.elvikom.co.uk
Jeśli skorzystałeś z mojej pomocy na Forum, możesz w ramach podziękowania wspomóc jego rozwój. Kliknij tutaj, aby dowiedzieć się więcej.
Jeśli skorzystałeś z mojej pomocy na Forum, możesz w ramach podziękowania wspomóc jego rozwój. Kliknij tutaj, aby dowiedzieć się więcej.
#3 Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on
by valieromarco • 26 December 2025, 14:43
After solder old chip nothing is changed but I saw that a resistor was missing and now I got up and down voltage on both coils L7520 and 7560 fro 0V to 0,5V
I checked pin + of battery connector is 12,5V but after 3 seconds drops to 4V for 3 seconds and goes back to 12,5V continuously
Voltages of U7501
1=0V
2=0V
3=0V
4=5V
5=0V
6=5,1V
7=0V
8=0V
9=0V
10=4,8V
12=3,42V
13=5,1V
14=5,1V
15=4,8V
16=0V
17=0V
18=0V
19=5,1V
20=0V
21=3,42V
22=3,9V
23=12,5V
24=0V
25=0V
26=5V
27= 0V
29=5,1V
30=0V
31=5V
32=0V
I checked pin + of battery connector is 12,5V but after 3 seconds drops to 4V for 3 seconds and goes back to 12,5V continuously
Voltages of U7501
1=0V
2=0V
3=0V
4=5V
5=0V
6=5,1V
7=0V
8=0V
9=0V
10=4,8V
12=3,42V
13=5,1V
14=5,1V
15=4,8V
16=0V
17=0V
18=0V
19=5,1V
20=0V
21=3,42V
22=3,9V
23=12,5V
24=0V
25=0V
26=5V
27= 0V
29=5,1V
30=0V
31=5V
32=0V
#4 Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on
by ado • 26 December 2025, 20:02
Start by measuring the resistance to ground on PP3V3_S5. PP5V_S4/
Your initial decision to replace U7501 seems reasonable. Since EN is present, it confirms that SMC is alive and has allowed the power-up sequence, which is a good sign.
However, there may still be a short or abnormal load downstream of the PMIC. The rather abrupt reaction after the replacement suggests that U7501 could be shutting itself down due to protection mechanisms, such as OCP or OVP, rather than a control or firmware issue.
Edit Ai:
In Apple boards, standby lines like PP3V3_G3H are always live, but 5 V rails tend to be more vulnerable to shorts from I/O, USB, or other peripherals. Check these rails carefully before concluding that U7501 is faulty.
Your initial decision to replace U7501 seems reasonable. Since EN is present, it confirms that SMC is alive and has allowed the power-up sequence, which is a good sign.
However, there may still be a short or abnormal load downstream of the PMIC. The rather abrupt reaction after the replacement suggests that U7501 could be shutting itself down due to protection mechanisms, such as OCP or OVP, rather than a control or firmware issue.
Edit Ai:
In Apple boards, standby lines like PP3V3_G3H are always live, but 5 V rails tend to be more vulnerable to shorts from I/O, USB, or other peripherals. Check these rails carefully before concluding that U7501 is faulty.
#5 Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on [SOLVED]
by valieromarco • 27 December 2025, 02:45
Re: Macbook Pro 13" A1502 motherboard 820-3476A Orange led no power on [SOLVED]
by Google Adsense [BOT] • 27 December 2025, 02:45
Who is online
Users browsing this forum: No registered users and 3 guests
_______________________________All rights reserved. Unauthorised copying of this website's content or any of its part is strictly forbidden.
Any trademarks, brand names, products or services published on this website belong to their legal owners, are copyrighted and used for information purposes only.