Luckfox Forums

Hi,
I've made custom camera board based on Pico Pro Max. But currently I cannot go into maskrom mode.
Cannot use recovery button to program with usb connection. The debug UART keep printing RKUART.
Have I missed any critical condition in the design so that the chip cannot boot?

The schematic doesn't look like an expansion board based on Luckfox Pico Pro Max. Let him show you the actual product photos

Hi hung.ng,

I encountered a problem very similar to yours. I also made a custom board using the RV1106Gx chip, that repeatedly prints "RKUART" to the serial console. I did some research and stumbled upon a very critical error, that I did, which I found in your schematic too:

As psirust describes in this post (viewtopic.php?t=812), there is an error in the schematic which is published for the luck fox pro max (which I used as a reference design). I used the 1.8V rail to supply my DDR_VDDQ[1..3] pins (and it looks like you do so too), but it seems that those pins are only 1.35V compatible. My guess is that this might be the reason for the faulty behavior.

Did you find any other source, or maybe even a fix, for that problem?

[EDIT]: To verify this theory, I just replaced the RV1106 on my luckfox pico pro board with the one I've used on my custom board. Now the chip on the luckfox board also repeatedly prints "RKUART", so I guess the wrong DDR_VDDQ voltage permanently damaged the chip.

Best regards
olel