[MTCD  Android Head Units Q&A] marchnz:
This Post details how OTG/LOADER can be achieved to recover a corrupt PX5 or PX3 - any RockChip MTCx SOM

Update 2/2018 - anyone can make a gig without modifying their main board. BUT FIRST try a USB port, some have OTG out of the box.

From the work I've now done, Ive realised you don't need to hack your mainboard. You could temporarily solder connections to SOM o

r make JIG from header pins or make a simple cable from an old USB cable and two resistors:

see: https://xdaforums.com/android-auto/...px3-5-headunit-mod-recover-flash-som-t3766892

Making a jig is necessary , as

MCU cuts power to SOM after a few minutes during OTG

.( Theory is the MCU watchdog senses an unknown condition in SOM, so resets by power off.) This can be bypassed by another mod to board, but much easier to just make a simple jig.

Need:

Remove SOM from mainboard.

Header pins to fit SOM (or solder temporarily to SOM PCB header)

USB male cable, cut one end off for wires to attach to SOM.

5v and 3.3v power supply.

1. Using schematic as guide. Connect earth and +5v pins. Connect 3.3v to [rtc_3.3]

2. Connect USB wires to SOM [USB-OTG] connections

3. Connect wire to SOM [ctl_recovery] and wire that to 3.3v.

Colour codes & Notes:

GREEN = PSU Earth [0v/(-)]

RED = +5v to PSU

BLUE = USB

YELLOW = +3.3 Via 3.3v supply OR use two resistors as a voltage divider 10K to 5v (R1 in image), 15k to earth (R2 in image), center = 3.3v

NOTE: SINK [CTL_WAKEUP) to GROUND (0v) if unit does not power ON

+5v = 1,2,3

0v = 4,5,6,71,72,73 and SOM Mounts

+3.3 = 20,28 (and possibly 9 & 15 - see note re. 15.)

With USB connected, power on. Use tools/load driver as described in recovery thread.

Q/Why hardware mods?

A/Mods were necessary because out-of-the-box (default) both my GS and JY boards would not enter USB OTG/Loader mode to connect it to a PC for recovery. We now know that a "jig" can be made without sacrificing your mainboard and simply wiring to header pins or buying a SOM header from say Digi-Key.

- Your MTCD may be different -so test first!

Q/My SOM won't appear in device manager or Rockchip Android tool

A/ If all connections are correct and power is Ok, force MASKROM as detailed here:

https://xdaforums.com/sho...&postcount=128

https://xdaforums.com/sho...&postcount=129

***Updated 08/Dec/2017 - Attach image showing USB Male cable connections to mainboard***

** Note - SD recovery boot card did not work for me on PX5 - probably due to version of [rockchip sdcard image create tool] - if anyone has a version that works, please post here.

Updated Feb 2018 - Android 6 SDCARD create tool is now available. Recommend SDCARD method and then OTG if SDCard method fails

Synopsis

My corrupt NAND was successfully reflashed using OTG "LOADER" mode as follows. It became corrupt , stuck in a bootloop and unable to enter recover following flashing a custom (bad) firmware image file.

- Using an MTCD GS board - which I have as a spare part - no display, only board.

+ Windows 10 x86 notebook with rockchip batchtools v1.8, rkimagerepack tool, latest PX5 image.

+ USB stick formatted fat32 with latest PX5 image

Do not do the below mainboard mods, this is completely unnecessary and posted for background on the journey to find a simple way of getting OTG.

1. Modified the board as follows:

A. Desolder and lift pins 27 & 28 of USB hub GL850 (thanks to xda user @ikerg and 4pda - for the lead)

B. Solder Male USB a cable to GS board USB 1 connections (See below attached image showing where USB male plug wires were soldered)

C. Remove pin to RK PX5 SOM [ctl_recovery]

D. Solder a wire directly on PX5 SOM header on [ctl_recovery]. This wire is used to trigger recovery.

Process

Initial recovery image: Because the PX5 firmware (OTG) "LOADER" process timeout appears to be approx 1 minute, it was necessary to create a recovery only image, as the 1.2gb PX5 firmware file exceeds the timeout, aborting the flash.

Using RKIMAGEREPACK, I created a image with a dummy zero byte system.img. This resulted in a 200mb image file.

- Loaded [rockchip batch tools] on notebook.

- Installed rockchip drivers

- connected USB cable to notebook

- held [ctl_recovery] wire to [mcu 3.3v test pad]

- Powered headunit on

- Notebook 'USB chime' was heard and board became connected, as indicated as highlighted '1' in rkbatchtools

- wiped flash

- selected firmware image without system created above and flashed to PX5

- powered off, removed PX5 SOM and refitted to JY headunit board

- On JY headunit, powered on, entered recovery via [holding powerbutton for approx 15sec - wait for 3 flashes of led] press once more.

Successful boot into recovery - started booting recovery and warned that system image was not valid. PX5 self-formatted system and awaited image.

- inserted USB stick with latest PX5 image and upgraded.

First boot waited for 5 minutes. Pressed reset and rebooted -

successful recovery!

The warning here is that the PX3 SDCARD image create tool does not work for PX5 - even when using a PX5 image.

Why did I post this? Original Post:

I have a (JY) MTCD with HA 2..56 MCU PX5 stuck in a boot loop - "starting apps" appeared and then it reboots, looping. I was unable to access recovery via any of the standard recovery processes (e.g.holding the power button or boot into recovery via bootable SDCARD.

========================================

On SDCard boot - works OK on PX3 but on PX5, only a black screen is displayed without any text.

SDCard and button holding recovery methods worked OK on PX3 board, but not the PX5 Module when the SOM NAND was corrupt.