Appologize deeply for my mistake for this problem that the red led aways lights and power fail.
I describe it here and try my best to do some rescue.
features: The red LED aways lights even pressing power button,fail to power on. It now aways appearance, it is a small probability event, but will lock the CPU into recovery mode even power again (recovery mode is one of the CPU modes, waiting for download the image from USB cable). Two ways to rescue the device, replace the resistance to a 47K resistance, or update image to remove the power button function.
route cause: There is a up-pull resistance to a aways on power VCC_RTC to drive the LED. For the resistance value 1K is too small to lead a 1.2V leakage to the CPU and then to eMMC. The eMMC power should be no power supply when waiting pressing power on button, but there is 1.2V exist.
solution: two ways: 1,replace the 1K resistance to 47K, the leakage will be lower than 0.4V, which is in safe state. 2,remove the state waiting pressing power on button in the software. The first method is adopted all the way, but this time a SMT error takes place.
Why we hadnot notice it so many long times? We had used two eMMC chips. We had noticed this leakage when introducing the new eMMC, so we update the BOM the same time using new eMMC. But this batch manufacture at 20150910, it is 2380 pieces,there is a package old eMMC 1360 piece need to be used .The SMT switch to the old BOM in the view of the old eMMC and heard that the two eMMC is pin-pin compatible.
I upload a image for this issue. It removes the power button functions based on version 202K4.
feature: 1, the same as 202k4 except the POWER BUTTON function and OTA. such as, 720p60 resolutions and Mbox logo.
update method: USB cable.
download link:https://mega.nz/#!ooxkAIKC!bT9RYSycd...wgsDy4ktR2e2OY
This version do not have OTA . I will upload newer one with OTA tonight and will be updated and served the same as the normal version.
The attached picture signs the error resistance. If replace this resistance to 40K~60K ,it will be ok.
Sorry and thanks for you read the whole article.
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