L'iPhone 12 Pro Max di seconda mano non si avvia

10 giugno 2022Aggiornato 28 febbraio 2025Case studyREWA Team2 min read

Purchasing a secondhand iPhone 12 Pro Max can be a great deal—until you encounter issues like the phone not booting. A black screen with no response, even after charging, can indicate underlying motherboard problems. This guide will walk you through the troubleshooting process and repair steps to get your iPhone working again.

Modello: iPhone 12 Pro Max

Annunciato: 2020, 13 ottobre

Feedback del cliente

A customer purchased an iPhone 12 Pro Max from an online secondhand marketplace. Upon receiving it, they attempted to power it on, but the phone remained unresponsive with a black screen. Charging the device did not resolve the issue.

Risoluzione dei problemi

Smontare il telefono – Open the device to inspect internal components.
Check for Missing Parts or Repairs – Noticed missing shielding covers and previous repair traces.
Ispezione della scheda madre – Found evidence of prior repairs.
Test Boot Current with a DC Power Supply – The boot current remained fixed at 90mA, indicating a CPU issue.

Possible Causes:

CPU not working due to poor soldering or damage.
CPU working conditions not met.

Processo di riparazione

Step 1. Remove the foam and sticker

Remove the foam around the connectors
Remove the black sticker tape on the bottom side of the motherboard

Step 2: Separate the Motherboard Layers

Use a heating platform to carefully separate the two motherboard layers.

Step 3: Identify Previous Repairs

Inspect the motherboard and note previous repairs:

The baseband and Wi-Fi chips were previously fixed.
CPU had been repaired before.

Based on the boot current fixed at 90mA defect phenomenon, we can try to resolder the CPU to have a try.

Step 4: Resolder the CPU

Remove the CPU and inspect under a microscope.
Found two pads on the CPU chip had been fixed previously.
Scratch out the pad carefully.
Jump wires and form secure connections.
Use a UV mask and cure with a UV lamp.
Reball the CPU and solder it back onto the motherboard.
Place the motherboard into a test fixture.

Step 5: Assembly Phone Phone

Attach the screen and connect the DC power supply to trigger the boot sequence.
The phone powered on successfully, and all functions were verified.

Punti di forza

A fixed boot current at 90mA often indicates a CPU-related issue, such as poor soldering, missing CPU pads, or CPU damage.
Always inspect secondhand devices thoroughly before purchasing, and review the seller’s return policy to protect yourself.

Strumenti e parti necessarie

By following these repair steps, you can successfully restore an unresponsive iPhone 12 Pro Max and avoid common pitfalls when buying secondhand devices.