Question Dead PCB?

[jondem]

Hi, I have a WD120EMFZ that was perfectly working, and suddenly doesn't start. It doesn't make any sound, click or anything, and of course is not recognized by the system.

Reading the forum it seems that If i'm lucky enough could be "only" PCB problem. The PCB part number is 006-0B40385.

Using the picture on this this post as reference
https://forums.tomshardware.com/thr...acement-pcb-006-0b40385.3653260/post-22013595

I tested the 5V and 12V TVS Diodes using the 200 ohms range of a multimeter and I got a reading value near 125 (if I invert the probes I get a static 1). Are those values ok? What else should I tried?

Sorry if the information is rather incomplete, I'm rather new on this procedure, so I'll greatly appreciate any help.

Thanks in advance all

 

[fzabkar]

The diodes appear to be OK. Test the two tiny fuses nearest the SATA power connector. They should measure 0.0 ohms.

This thread has more detailed info:

https://forums.tomshardware.com/thr...ves-and-they-are-no-longer-recognized.3739967

 

[jondem]

Hi @fzabkar, thank you so much for your quick answer, was reading several of your posts and you know a lot about these issues so greatly appreciate your help.

When testing fuse 1 i get almost 0 ohms (00.5) on the 200 ohms range.

But for the fuse 2 the multimeter shows a static "1" value, no matter the order of the probes. Maybe that could be one of the problems?

 

[fzabkar]

Fuse #2 is open. If there are no other problems, you can flow a blob of solder over the fuse.

That other thread shows you how to test for shorts at the other on-board supply voltage test points. Basically, you test the resistance between each inductor and ground. If there are no more shorts, then you should be good to go.

I would suspect that you have a PSU problem. Either that, or you used a modular cable from a different PSU. Please make sure you sort out this problem before powering up your drive.

 

[jondem]

Yes I do in fact think there was a PSU problem because I have two disk with the same problem, and both of them stop working at the same time. My terrible big mistake was using one Molex to 4 Sata Adapter, will never use something like that again.

In case the only problem is the fuse, is it better to flow a blob of solder over the fuse, to replace the fuse or to directly replace the PCB?

 

[fzabkar]

Are you able to perform micro-soldering?

If you replace the PCB, you would also need to transfer the "ROM" chip, or engage someone to do it for you. If you damage it, you will be in big trouble. That said, some PCBs have a unique security key in the MCU chip, so a PCB swap cannot work. I don't know if your PCB is one of these.

Overall, I think that blobbing the fuse is less risky for a first-timer. Since the diodes are not shorted, the possibility of additional problems would be low. It's your choice, though.

 

[jondem]

Thank you very much! Not having to replace the PCB would be a huge pro.
Can I ask you what are the eventual cons of just blobbing the fuse? I know someone that can do the micro soldering for me if that is preferred and worth it.

 

[fzabkar]

Earlier HDD designs had no fuses, just the TVS diode. When the TVS diode was short circuited by an overvoltage, the computer's PSU would see the short and then shut down.

Your PCB has two electronic fuses in the 24-pin "8237" chip. Those would be the next level of protection. If there were any more problems, that would be the first place they would show up.

 

[jondem]

Hi fzabkar, sorry to bother you again. I was checking the other thread but notice that the PCB used as reference was different.

Would you be so kind to point me the right points to test resistances on the 006-0B40385 PCB?

By the way, I was checking the PCB from the second disk I mention, is a 001-0A90601 from a WD120EMAZ. On this PCB I notice same measures for TVS diodes, reading value near 125) But for fuses, I notice near 0 for one of the fuses, but the other give me a reading near 150 on the 200 ohms range (not 0 or a static 1 as before).
Here is the PCB pic just in case

 

[fzabkar]

Measure the resistance between ground (a screw hole) and each of the voltage test points.

http://users.on.net/~fzabkar/HDD/0A90601/

The fuse that gives you a reading of 150 ohms is open. It needs to be replaced or bridged.

Just FYI, this chip is the second level of protection:

http://www.hddoracle.com/download/file.php?id=9506&mode=view

 

[jondem]

Bridge both fuses and both disks are now working. You're the man @fzabkar , thank you so much.