Full AOSP on MStar Cedric3 head unit

Hi!

I bought it on eBay one head unit with the following originals characteristics:
CPU: Cortex A9 Dual-Core 1Ghz
GPU: Mali 400
RAM: 1GB DDR3
Android Version: 4.4 (but really is 4.2)
MCU original Version: 4.3.11-1-03-615101-150112
System Version: 2.9.5_20150413

Anyway, I tried to update the MCU with the head unit who brought extra settings -> model choose, but the upgrade to 4.3.13 everything works fine except the lights that indicate the volume level, and that is not moved up or down the volume.
I suppose that changing the MCU has stopped working. How could recover the original MCU?
I contacted the seller, but no longer sold items on eBay and I doubt I answer.

Thanks in advance!!

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