DRA756: CPU DRA756 not working, power short circuit!

Hi,

Please tell me more about the board. Is it a customer-made board? Board schematic will be helpful. E.g. you can send me by email.

Also, I didn't understand if some board are operational and only few boards fail? Or, they all fail?

Common causes for short circuit on power rails could be:

- short between tracks on PCB

- shorted or reverse mounted bulk capacitor or a diode

- short in the load

Thanks,

Stan

Hi，

1、These boards are produced by our own factory；

2、At present, we only delivered 30 PCS, and found 3 pieces of defective; Therefore, it is not sure whether it is a batch problem or not. At present, there are some common problems;

3、At that time, it was suspected whether it was caused by the plug and insert of SD card. ESD experiment was conducted on the SD card, and no similar abnormality was found.；

VDDSHV8 power fail  

What are the possible causes of power failure?

HI：

    PE1 The ground where the fixing screw holes are connected to the core plate；

    As green as the bottom

    Could there be some other reason for the power short circuit?

My question was little bit different.

If we look at the PCB preview from your latest post:

Is the PE1 plane  connected (and how) to the digital ground plane (named  'GND' and shown on the same PCB preview)?

If yes, is it a 0-ohm resistor, a capacitor, an inductor, or other?

Regards,

Stan

HI：

    PE1 is connected to the screw hole of the core plate, which is connected to the power supply GND by 10nF capacitor；

   In addition to the power supply mentioned above, this power supply EVM3V3  also appears to reduce the impedance to the ground。

  What could be the cause analysis?

Hi,

I would proceed as follows:

1. De-solder all ESD protection diodes

2. see if all shorts on the PCB related to SD card disappear

3. check all desoldered diodes for short-circuit failure

Regards,

Stan

Hi,

No diode short circuit has been found in the current test. Is there any other reason besides this?

Please try to jump (short) the 10-nf capacitor. Check if power supplies are normal.

HI：

Now I find that the three boards with problems are as follows:

1. one PCS：The impedance of MMC1_CLK and MMC1_CMD of a board to the ground is 0R;

2. other PCS：The MMC1_DET impedance of a board to the ground is 0R;

What causes the SD card's signal line to be unusually short to the ground; The VDDSHV8 power supply of these two boards also shorted to the ground; At the same time, MMC1_SDWP signal is not used by SD card at present. Now we pull up 47K to VDDSHV8，MMC1_SDWP is currently grounded

. Is there anything wrong with the design of this signal?