Shorted WD 12TB - Help Making sense of TVS/Fuse Readings

Hey Everyone,

I made a fatal mistake by swapping out my powersupply in my NAS without swapping the SATA power cables and ended up shorting 3 of my 12TB drives. They don’t power up.

Taking a look at the PCB, nothing is fried or burned. With this diagram from another thread:

Left 12v TVS diode reads 277 kohms. Right 5V TVS Diode is all over the map as it goes from 100 kohms to 1mohms and back down and up continuously. The left 12v fuse makes my autodetecting voltmeter beep and go into continuity mode and reads 0 ohms. The rightside 5v fuse I can’t get a reading/detection from my voltmeter.
What does this tell me? Is the left fuse reading OK and it’s the 5v fuse on the right that is dead?

Big thanks in advance for any help!

The 5V fuse is open circuit. If there are no other problems, you can bridge the fuse with a blob of solder. Of course it’s better to replace the fuse, but most end users have no soldering experience.

That said, I usually advise people to test for shorts at the onboard power supplies. I could help you with that if you could provide a detailed photo of the PCB.

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Big thanks for the response! I was thinking of just bringing it to a electronics repair store and see if they can replace the fuse. Here’s a pic of my PCB:

Measure the resistance between ground (any screw hole) and each of V1, V4, V5, V6 and Vneg.

This is a similar PCB:

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V1: 4.46 kohms
Vneg: 0.9 mohms
I’m really struggling to find V4,V5,V6 as the board layout is quite different.

There are 3 inductors (the larger rectangular, 2-terminal components). Measure the resistance between their terminals and ground. The circuit is electrical identical in this area, although there are cosmetic physical differences. Note that any two points connected by a copper trace are at the same electric potential.

(I’m using my other machine ATM, so I cannot annotate the image)

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Oh gotcha I think I got the right points.

There are no shorts, so you should most probably be OK. Just deal with the fuse, that’s all.

I recall two similar cases at Tom’'s Hardware. One person recovered all his drives by flowing a blob of solder over the 5V fuses. The other person was able to recover all but one.

If you run into further problems, then a PCB swap and firmware (“ROM”) transfer might get you going. Your PCB has two ROMs, MX25U1631F (8-pin). These chips store unique calibration data.

This chip provides second-level protection by way of two electronic fuses:

You would be very unlucky if the overvoltage punched through it and damaged any downstream components. In that other case, this IC was damaged.

BTW, you can use a leaded picofuse. Just wire one lead to the +5V SATA power pins and the other to the striped end (cathode) of the TVS diode.

The rating of the 5V fuse is usually 2A. The 12V fuse is usually 4A.

Good luck.

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Awesome thanks again man, you’re a life saver. I’ll contact a local electronics repair store and see if they can either replace the fuse or do as you mentioned.