Question Repair an overvoltage on Seagate 7200.12 Hard drive

caffelatte

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I have a hard drive I removed, put into an external hard drive caddy (which worked), then returned to my PC and it didn’t read then I think I smelt some burning, then later tried again in the external caddy and it didn’t work (spin).



I posted online asking for help years ago and was advised the problem was caused by an overvoltage on the 5v input. I never got around to following the steps to fix it, and I’ve now just ordered the tools needed to make the fix and realised I have a few questions that I’m hoping to get answered.



The steps I was given before were:



1. Once you can trust your PSU, you should remove the shorted 5V TVS diode. You can simply snip its pins with sharp pointed, flat jawed flush cutters. http://www.users.on.net/~fzabkar/HDD/ST31000528AS_TVS.jpg

2. Then you need to clean up the charred remains of the inductors with a toothbrush and isopropyl alcohol (audio/video head cleaner).

3. Finally you need to rebuild the path from the +5V pins at the SATA power connector to the cathode (striped end) of the 5V TVS diode. Use a short length of insulated wire as follows:

http://www.users.on.net/~fzabkar/HDD/5V_TVS_fix.jpg

4. Test the board on its own before mounting it on the drive, and confirm that the supply voltages are correct.








When working through the steps I was given before, my questions are:



1. How do I re-attach the wire? Solder? Yes

2. Which pins do I attach it to? (Counting from the left, it should connect to pins 7-9?

3. Do I just put a blob of solder across all 3 pins and connect it to the wire, then wire the other end up to the cathode? No.

4. What type of wire should I use? I just bought a soldering kit that came with some red & black insulated wire – I assume either would work?

5. How do I test the board on its own? I've just bought a multi-meter, but what parts of it should I test? (or what are the right search terms to find instructions)

6. If I were to replace the diode, would it be a stable drive, or should I just scrap the HDD after recovering the data? (from the looks of things the inductor is completely burnt out?)

This is all new to me, but I'm finding this all really interesting. Thank you in advance for taking the time to answer.

Pictures of the HDD:

Board
Close up
HDD Specs
 
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USAFRet

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4. What type of wire should I use? I just bought a soldering kit that came with some black wire – I assume that would work?

5. How do I test the board on its own? I've just bought a multi-meter, but what parts of it should I test? (or what are the right search terms to find instructions)
If this is your first lap around the track with a soldering iron, you really need to practice on some non-critical part.
It would be easy to make this drive PCB worse, not better.
 

digidoggie18

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It sounds to me like you don't know how to solder just yet. I highly suggest practicing to get it down as it is really an art. Once you do that, I would then revisit this. When testing the board on its own. I would plug it in and backprobe the power pins to see what voltage you are at. another way you could help facilitate this is just by probing the 5v rail right out of the PSU. Keep in mind that the circuit is not under load while doing this so you could get a higher skewed reading which is why it is suggested to test with the board. I would check out the tolerances of said PSU by looking at the spec sheet as tolerances can vary from 1% all the way up to 10% and is very hardware specific. You will attach everything via solder. As for blobbing it across all three pins absolutely not as that could create a short especially with the repair you suggested. With that beiong said a soldering iron is not the best tool to use in board repair like that. The best tool you can use is a pen that blows hot air. It is my preferred method along with solder wick to clean everything up vs a solder sucker. liquid flux would also be a good idea too, make sure you wipe up all excess though or it will cause corrosion. With the hot air pen you can literally clean all the solder off, tin the board, heat everything and that diode will wick itself into place causing less issues. If you have any other questions in regards to my reply please ask. This is not a minor procedure you are performing although for guys with the knowledge already, it is very much like that. I always recommend back probing with everything in use with a good back probe kit. Have you actually tested the diode yet to know for sure its bad and just not that its a bad connection?
 

caffelatte

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I've got a practice PCB. So I'll be practicing with that. I don't have a back probe set. I've tested the diodes and found:

Measuring 5v and 12v diodes, both ways with 200 ohms range that both readouts were 1.

Using the continuity check it beeped on the 5v diode in both directions, but showed a 1 on the 12v.

As I understand it, this shows the 5v diode to be at fault? So, I should follow the steps above?

The soldering kit included flux and solder wick & sucker. I've watched quite a few YT vids of diode removal and I have an attachment to get a sharp point on the iron so I'm confident I can manage without a gun.

So I attach the wire to which pin? 7, 8 or 9 ?

I was confused by what you said about wicking the diode into place - is that assuming I replaced it? Would I also need to replace the inductor as it's melted into a blob. It sounds like it's safer to just scrap the HD.
 
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The 5V TVS diode should have measured 0.0 ohms on the 200 ohms range, or near enough to it.

You can remove the 5V TVS diode by snipping its pins.

Clean up the charring with isopropyl alcohol. Scrape away any black, carbonised areas. These are conductive.

Solder an insulated wire between the striped end of the diode (marked with a "v" on the PCB) and pins 7, 8 and 9 of the SATA power connector. These will all be connected together, either on the PCB or at the PSU.
 

caffelatte

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I've snipped the diode and then done two rounds of cleaning with a toothbrush + iso. It still seems quite dirty. Is it okay to be quite firm with the toothbrush?

Sufficiently clean?

Plan

So I'll use flux on point A, followed by solder wick. Re-flux & freshly solder some insulated wire. Then flux & solder the other end of the wire across the three pins.
 
Measuring 5v and 12v diodes, both ways with 200 ohms range that both readouts were 1.
You can't check if a diode is working by use ohmmeter, you need to use a diode tester (which is often a built-in function in most multimeters)

Using the continuity check it beeped on the 5v diode in both directions, but showed a 1 on the 12v.
This depends on the multimeter used. According to Fluke, that is just another way to measure ohm.

As I understand it, this shows the 5v diode to be at fault? So, I should follow the steps above?
Not necessary. The diode is still part of a more complex circuit. You measure the parallell circuit of the diode and whatever pile of components and ic's that makes u the rest of the circuit.
Unless you either physically remove the diode and make a proper diode test on the diode only ; or have the means of knowing the excact circuitry around the diode - there is no way of confirming the diode are the faulty component.


The 5V TVS diode should have measured 0.0 ohms on the 200 ohms range, or near enough to it.
No, that is wrong. You don't use a ohm-meter to determine if a diode are faulty or not.
 

caffelatte

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I've had a go. It was a lot harder than I thought and I should've used a longer piece of wire and smaller attachment on the soldering iron - an extra hand would've helped too.

Can anyone give opinions on whether I've messed anything up majorly that's visible - From the close up in image 5 below it appears that I might need to solder wires 8 & 9 together?

What tests can I do to see if it might work?


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You can't check if a diode is working by use ohmmeter, you need to use a diode tester (which is often a built-in function in most multimeters)


This depends on the multimeter used. According to Fluke, that is just another way to measure ohm.

Not necessary. The diode is still part of a more complex circuit. You measure the parallell circuit of the diode and whatever pile of components and ic's that makes u the rest of the circuit.
Unless you either physically remove the diode and make a proper diode test on the diode only ; or have the means of knowing the excact circuitry around the diode - there is no way of confirming the diode are the faulty component.


No, that is wrong. You don't use a ohm-meter to determine if a diode are faulty or not.
The OP is testing for a short on the 5V input. He is not measuring a diode. Indeed it is impossible to correctly measure the diode since it is connected directly across the supply. We are in fact measuring EVERYTHING on the 5V rail.

Moreover, since we are only interested in whether the diode is shorted or not, then the 200 ohms range is what we need. The diode test range risks turning on other PN junctions, so that will only complicate matters. In the present case, and in almost all cases of overvoltage involving HDDs, we don't need to perform elaborate tests. Trust me, I've been through this same scenario hundreds of times in the past 10 years in the storage forums.

Edit:

The reason I said that the OP should measure 0.0 ohms for the diode is that all the signs point to it being shorted. I did not mean to imply that a good diode should measure 0 ohms. That would be ridiculous.
 
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I've had a go. It was a lot harder than I thought and I should've used a longer piece of wire and smaller attachment on the soldering iron - an extra hand would've helped too.

What tests can I do to see if it might work?
It's not the prettiest job, but it should work. I would cover the wire with some insulation tape in case the strands contact the body of the drive.

As for tests, power up the PCB on its own and measure the voltages between ground (eg a screw hole) and the two TVS diodes. You should see +5V and +12V.

Next measure the voltages at the two coils near the SH6968B motor controller IC (at 10 and 11 o'clock).

https://s.yimg.com/aah/yhst-14437584971410/918062927-1.gif

One coil is octagonal, the other is circular. These will be the Vcore and Vio voltages for the MCU (the big square IC).
 

caffelatte

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The OP is testing for a short on the 5V input. He is not measuring a diode. Indeed it is impossible to correctly measure the diode since it is connected directly across the supply. We are in fact measuring EVERYTHING on the 5V rail.

Moreover, since we are only interested in whether the diode is shorted or not, then the 200 ohms range is what we need. The diode test range risks turning on other PN junctions, so that will only complicate matters. In the present case, and in almost all cases of overvoltage involving HDDs, we don't need to perform elaborate tests. Trust me, I've been through this same scenario hundreds of times in the past 10 years in the storage forums.

Edit:

The reason I said that the OP should measure 0.0 ohms for the diode is that all the signs point to it being shorted. I did not mean to imply that a good diode should measure 0 ohms. That would be ridiculous.
Thanks, both for the additional steps and information. I ended up testing the removed diode for continuity and it had shorted which gave me the confidence to proceed (along with checking I hadn't mis-soldered anything about 10 times under magnification)

I then soldered pins 8 and 9 together so there was a solid connection using a finer solder tip and cleaned up the wire to make sure nothing was touching and any stray wires were contained.

I actually already plugged it in before the last message, so didn't run any of those steps.

The drive worked fine and I managed to pull off all of my pictures and some media.

Thanks so much. You've saved me hundreds in recovery costs and helped me to gain some new skills.
 

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