Hi, I have several HGST drives that were connected in a NAS and unfortunately the wrong PSU was plugged into the NAS today and gave 18V instead of the expected 12V. After this happened, the drives no longer spin up or appear to work at all. I read online that simply replacing the PCB would not be the way to go, I am handy with a soldering iron / rework station but I am unsure where the TVS is on this unit and how to replace it.

Here is a zoomed in photo of the components where I think the TVS is placed, the top right component is connected directly to 12V but i dont get a reading from GND on the other side. I am unsure how to take a diode reading with my multimeter, but in one of the options this component on the top right is labelled XH and gives 000 when I read it, everything else like capacitors or the Z4 component gives some kind of reading. The component labelled XH on the top right of this image is giving a resistance reading of 0.



Here is a full picture of the board.



If anyone can help me identify where the fuse and TVS are then I can try to remove those and hopefully they shorted out the board. When I connect the drives in a cradle via USB the device shows up with nothing just an empty device so it seems to know that there is something plugged in but cant read or interact with the drive. The cylinders arent firing and the drive appears t be totally dead. Any help greatly appreciated!!!

Quick update, I tried removing the component labelled XH (top right of the photo) and powering in an external bay with the pad shorted, this didn't work at all and the bay refused to even power - I have since put the component back on the PCB and its behaving exactly as before, powering up but no disks starting or ability to access the data.

If you have access to a working PCB make sure that firmware listed on drive label is the same and move Winbond flash chip from not working PCB to good one.
Make sure that PCB is from the same family (Ultrastar 7k6000). It may be lower capacity.

Normally what happens is that the 12V TVS diode becomes shorted and the associated fuse goes open. However, your measurements would tend to discount this. Are you sure that "Z4" is not measuring close to zero ohms? The fuse may in fact be a resettable polyfuse.

One other possibility why the drive doesn't spin in an external bay may be that there is 3.3V on the Power Disable pin. This pin should be at 0V to enable power to the drive.

When you power up the PCB, do you measure 12V and 5V at the TVS diodes?

_________________
A backup a day keeps DR away.

The two fuses you highlighted are showing 0 ohm reading for resistance, the 5V TVS shows a 2.2k Ohm resistance and the 12V TVS shows a reading close to 0, it starts to read it and then drops down to 0 for reading.

If I remove and bridge the fuses and 12V TVS is this a likely appropriate step to fix the drives?

The fuses are OK. Just remove the 12V TVS diode. Don't bridge anything.

_________________
A backup a day keeps DR away.