Today, I am repairing a backlogged board sent by a Taobao user, the Changhong ZLS47HIS-V1 motherboard, some small capacitors are missing. The main chip is MSD6A818, powered by 12V+24V, with a Nor Flash+EMMC combination.
The symptom is that the power light is on but it won’t boot. Connecting to the programmer, the printed information is as follows:
The problem is basically locked in the EMMC related circuit, which includes the EMMC itself, its working conditions, and the main chip. Taking a step-by-step approach, I first checked the working conditions and the EMMC.
Starting from the power supply, the 3.3V supply is split into two paths, one goes through FB4 to the EMMC; the other goes through a 10K resistor to each IO pin. I found an issue with one of the paths and replaced it.
The printout came out and entered the console (the previous person might have cleared the EMMC), I copied the main program to a USB drive for upgrading but found that the files on the USB drive could not be recognized. I can enter the console but cannot upgrade. The factors causing this include: USB drive compatibility, USB circuit, boot mismatch, main chip, etc. I replaced the USB drive and tried upgrading again.
After the upgrade, the logo loaded but then the screen went black. I removed the EMMC and read it offline, which was normal. The EMMC can basically be ruled out as the issue, the problem is still with the hardware. Continuing to focus on this circuit for repairs, there are not many components around the EMMC. I found that the surface-mounted capacitor (C1000) on the VDDI pin was missing, so I found one and installed it, resolving the fault.
When repairing surface-mounted capacitors, I always feel they can be optional, but this habit needs to change.
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