Component identification: capacitor

userHead msrego 2019-12-06 00:48:03 3976 Views2 Replies
Hello,

Before anything else, I want to thank all the community for all the help given in order to troubleshoot the boards that have powering problems.

I was using my Alpha 864 board as usual, powered via the supplied USB-C adapter and it shut itself down. After suspecting a bad power supply I tried to power it from the 12V header, but still no LEDs, neither the blue one nor the red would turn on. I also bought an USB-C PD adapter with the 15V mode and I had the same result.

After measuring the rails, I arrived to the conclusion that power was being supplied to the first input MOSFET, but the second one (for both the 12V and the 15V USB-C PD rails) would not conduct, leading me to suspect that the overcurrent protection was being triggered.

So, after probing the main power rails, I discovered that the MLCC encircled in red in the attached image was shorted to ground.
This capacitor is in the DC/DC converter near the M.2 E key connector, just above the MOSFET which is in between the coil and the main output tantalum capacitor for this DC/DC converter. After removing the MLCC, I got both LEDs doing their normal activity, and my board powers up normally.

I know it is probably an decoupling cap, and that the board will probably work normally without it but I would like to replace it. The problem is that I don't have any way to know the correct specifications for such cap. I would be very grateful if anyone could help me identifying this capacitor.

Edit: I don't know if this post is in the correct section, or if it should be in the technical discussion section. In that case, I kindly ask the moderators to move this post to the adequate section. Attachments IMG_20191205_031142__01.jpg IMG_20191205_031142__01.jpg (646.08 KiB) Viewed 3831 times