SanDisk 128G help

[Core.iStores]

no continuity between Vcc and each of the 2 x 6 pins

That means that the controller must be generating the 3.3V supply for the MUX IC. This suggests that those small ICs are protection devices or perhaps they are switches?

I'm wondering whether this flash device is idiot proof. I'm thinking that it would be possible for a user to find a way to power both ends of the drive at the same time. This could potentially damage one or both USB hosts. Perhaps one of these ICs is intended to protect against such a scenario?

In the absence of power, I would test for continuity between Vbus-3.0 and Vbus-C. If they are connected, then this means that there is no protection. If they are not connected, then I would test for continuity between each of the Vbus sources and each of the pins of the two ICs. If both Vbus sources are connected to the same IC, then this would suggest that this IC is a power selector switch.

only D- (USB) to D- (Type-C) & D+ (USB) to D+ (Type-C) pins that are connected together

[fzabkar]

If I understand correctly, you have determined that there is no connection between Vbus_3.0 and Vbus_C. This means that the flash controller is not being powered directly from either USB connector.

The simplest way to implement power "OR-ing" is via two diodes:

Code:

  Vbus-C    o---->|--.
                     |   .-----------.
                     +---| controller|
                     |   '-----------'
  Vbus-3.0  o---->|--'

I don't see any diodes on your PCB, so this would not appear to be how it's done.

An alternative method might involve a power selector switch using a single IC:

Code:

            .--------.
  Vbus-C  --| -o     |   .-----------.
            |   \--o-|---| controller|
  Vbus-3.0--|--o     |   '-----------'
            '--------'

This method leaves me wondering what the other IC does.

Here is a complicated power selector IC, but I think it should be possible to implement a simpler version with 6-pins:

https://www.mouser.com/ds/2/308/on%20semiconductor_cat6500-d-1194834.pdf

The third method could involve separate ICs for each power source:

Code:

            .------.
  Vbus-C  --|IC #1 |---.
            '------'   |  .-----------.
                       +--| controller|
            .------.   |  '-----------'
  Vbus-3.0--|IC #2 |---'
            '------'

The problem with this method is that it doesn't explain why the two ICs are different.

I would test whether any pins of the two 6-pin ICs are connected to each other. This junction would then be the power output to the flash controller.

Maybe there is an error in my logic, but that's how it looks to me.

[Lardman]

How are you powering USB 3 or 2 and what's the current.

I think I'd pull 72 clean up and recheck the thermals just in case it's actually the monolith getting hot under it. Check the voltages on the pads themselves whilst the chips off too.