The system does not see the disk, there is no power. It's about the board

What model?

HDD Western Digital My Book Essential is an excellent external drive, I already have a couple of them, albeit from different years. This particular model is WDBACW0020HBK-00. Here are its characteristics:

Capacity: 2 TB
Format: 3.5 inches
Interface: USB 3.0
Data transfer speed: up to 5 Gbps via USB 3.0, up to 480 Mbps via USB 2.0
Compatibility: Windows, Linux and macOS
Features: Hardware encryption, automatic backup using WD SmartWare software

What's the problem with the disk?

Everything started well. I bought it for 4 euros with a power supply and USB cable. The usual cost of such a device now on the secondary market is from 30 euros.

When I came home and connected it, the joy faded somewhat, since the LED on the front panel lit up, but the device did not show any other signs of life. Windows detected the connected disk, but showed that this disk was not initialized and did not display any characteristics in the list of devices.

At the same time, a suspicion immediately arose that the problem was not with the disk – there were no sounds when connecting. Usually the disk initializes, the spindles begin to spin up, and the LED begins to flicker. All this is accompanied by the usual sounds for HDD operation. If the disk is damaged, there are also sounds. There may be cyclical clicking, rustling, etc.

Another sign that the problem is not the disk – the power button did not work. The LED lit up when the power was connected and was on all the time, whether I pressed the button or not – it made no difference. But it shouldn't be like that.

In short, I disassembled the device and took out the HDD. I connected it to an external “pocket” for disks, and sure enough, the HDD itself is working (in the photo there is already a three-gigabyte hard drive. Looking ahead, I upgraded a device from WD with it). The standard disk, as I said above, turned out to be completely “healthy”, I sent it to my storage rooms, it will come in handy.

In short, the problem was with the board and that’s what I decided to fix.

Let's fix it!

The repair process began with checking the board for short circuits. I checked all the ceramic capacitors and mosfets – but there was no short circuit. Then I got to thinking – I have no experience in repairing such boards, but anything could have broken – from the mosfet (they don’t necessarily burn) to the BIOS chip, the firmware itself, or the processor.

If the problem is with the firmware or processor, the repair could be put off for a long time. There is no place to get the firmware, change the processor – the cost of repair will be more expensive than the same used drive. And it’s a pity for time; I don’t really need another external HDD. Another option is to find a donor board, but after a quick search it turned out that they cost the same as a new WD external drive of the same model now costs.

And then I began to think, trying to apply logic. I put myself in the shoes of an ordinary user. What could go wrong? A disk can be dropped, for example, but in this case the HDD itself will fail, but not the board. In addition, the user may accidentally connect the wrong power supply. Here the board is 12V, but laptops from ASUS have the same connector; perhaps the user could connect an adapter from a laptop, but they are 19-19.5V.

In this case, the board of the disk itself most often fails, the 12 V TVS diode “flies out”. The TVS diode (Transient Voltage Suppression Diode) is a device for suppressing voltage transients that protects electronic components from short-term voltage surges, such as static electricity (ESD), impulse noise and overvoltage. He may not be able to cope with 19V.

However, sometimes the external HDD board is also damaged. This is especially important if the bridge firmware includes hardware encryption, as is the case with WD My Book Essentials. In most cases, the damage is limited to the dual MOSFET switch. This is usually an 8-pin chip. The function of the mosfet is to switch +12 V and +5 V power to the SATA connector of the drive under the control of the bridge chip. The Gate pins are the control pins, and the Drain and Source pins are the switch inputs and outputs. In my case the mosfet was AO4619.

As it turned out, some boards on external HDDs do without such mosfets at all; they use a zero resistor. Here is a photo from one of the forums of just such a board.

Source

In general, I could try replacing the mosfet, but the problem is that I didn’t have either the AO4619 or its analogue. A quick fix idea is to simply short two pins on the board so that power flows directly. Of course, this is not a long-term problem – the board of the drive itself may burn out if something goes wrong with the power supply again. But as a test of the idea, the cause of the breakdown is quite a result.

What exactly needs to be shorted? Here is a photo from the same forum, which shows exactly what needs to be short-circuited.

Source

I did just that, connected the board, and voila – its behavior changed. Now when I pressed the power button the LED turned off. When pressed again, it turned on.

The last step of the test is connecting the drive to the board. And everything was fine too, the disk rustled, the spindles spun and the system showed everything as it should. After that I turned everything off, ordered a mosfet from Aliexpress and now I'm just waiting to replace the mosfet. In general, you don’t have to do this; it will work just like that if the power supply is reliable. But it’s better to do everything according to Feng Shui so as not to take risks, right?