Fried Smooth L7251 controller, possibly fried board WD 750GB

[SecretRaindrop]

The drive span up when i covered J1 with some ESD-safe tape.

[fzabkar]

That does appear to confirm that the preamp is dead.

[SecretRaindrop]

Then this is the end of the road for me :/
I would open up the drive and replace the arm, but im not sure how much a new one costs, and i dont think i have somewhere clean enough to do the job ^^

[Amarbir[CDR-Labs]]

Assuming that U12 was transferred correctly, then I expect that your preamp may be dead. Does the drive spin up if you place a business card between the PCB and the J1 contacts?

Unfortunately it appears that you are one of many victims of WD's bad designs. Ironically, if the fusible zero-ohm resistors (R64 and R67) had been replaced with wire links or blobs of solder, then your data would now be recoverable simply by removing a shorted TVS diode. However, because of WD's absurd design, these "fuses" not only do not protect your data, they are in fact responsible for your data loss.

Sir ,
Kindly Explain The Second Part Again i think i missed something here .i would like to comment after that

[ShaneWard]

after reading the messages about how the smooth controller got fried, could it be possible that the shorted preamp is forcing the power supply to ram more amps through the smooth chip and blowing it. Perhaps your home PSU is of a much higher amperage than then one you are using at work, so the board only gets hot and not blow because the PSU is at its max Amp output compared to your home one which could provide much more amps through the smooth chip.

If you can get hold of a second drive of the same type, then you can play with swapping heads in a clean room if you want. Perhaps find a simmuler drive with good heads and a bad PCB.

Shane

[fzabkar]

For a long time I used to think that WD's TVS diodes were configured as follows (because I was working from photographs and because I couldn't believe that anyone could be so stupid as to do it any other way):

Code:

                         .---------.
+12V  o-----------+------|         |
                  |      |  motor  |----> spindle motor
               D4 -      | control |
                  ^      |         |
           ___    |      |         |----> VCM
Gnd   o---|___|---+------|         |
                         ----------'
           R64

                  +-----------------------------------> preamp +5V
                  |
                  |      .---------.      .-------.
+5V   o-----------+------|         |------|Vio reg|---> MCU, SDRAM, flash
                  |      |         |      '-------'
               D3 -      |  motor  |      .-------.
                  ^      | control |------| Vcore |---> MCU
           ___    |      |         |      '-------'
Gnd   o---|___|---+------|         |      .-------.
                         |         |------| Vneg  |---> preamp
           R67           '---------'      '-------'


In such a circuit, the fusible zero-ohm resistors (R64 and R67) would go open circuit whenever the TVS diodes were shorted by an overvoltage, thereby disconnecting the incoming supply from the remaining electronics. Other HDD manufacturers (Seagate and Samsung) also use series-connected protection devices (zero-ohm resistor, polyswitch).

However, when I eventually got my hands on one of these boards, I found that the actual arrangement was as follows:

Code:

                .--------.
+V  o----+------|        |
         |      |        |
         -  D   |        |
         ^      |        |
         |      |        |
        .-.     |  HDD   |
        | |     |        |
        | | R   |        |
        '-'     |        |
         |      |        |
Gnd o----+------|        |
                '--------'


Now consider what happens when the drive experiences an overvoltage.

Firstly the diode goes short circuit, causing the "resistor" R to appear as a direct short across the supply.

Code:

                .--------.
+V  o----+------|        |
         |      |        |
         )  D   |        |
         |      |        |
         |      |        |
        .-.     |  HDD   |
        | |     |        |
        | | R   |        |
        '-'     |        |
         |      |        |
Gnd o----+------|        |
                '--------'


What happens next depends on the current limit of the external PSU. If the PSU is a 19V adapter such as is supplied with various laptops, then the supply's short-circuit protection circuitry usually shuts it down before it can damage resistor R. However, if the drive is an internal one, then the computer PSU's much higher current limit usually (?) blows the resistor open. When this happens the TVS diode is rendered ineffective, and the HDD's unprotected electronics is then hit with the full force of the overvoltage.

Code:

                .--------.
+V  o----+------|        |
         |      |        |
         )  D   |        |
         |      |        |
         |      |        |
         |      |  HDD   |
         o      |        |
            R   |        |
         o      |        |
         |      |        |
Gnd o----+------|        |
                '--------'


[ShaneWard]

So the preamp gets it power straight from the 5V Rail and not through the Smooth chip...

[fzabkar]

The preamp gets its +5V supply from the SATA connector, often via a small inductor (for noise filtering). Its negative supply (-5V) comes from an inverting buck regulator powered from the +5V supply, and with PWM control coming from the motor controller.

[fzabkar]

So the preamp gets it power straight from the 5V Rail and not through the Smooth chip...

Maybe this is a better diagram:

Code:

                                                       .------------.
                  +----------------------------------->| +5V        |
                  |      .---------.      .-------.    |     preamp |
+5V   o-----------+------|         |------| Vneg  |--->| -5V        |
                  |      |         |      '-------'    '------------'
                 D3      |  motor  |      .-------.
                  |      | control |------| Vcore |---> MCU
                 R67     |         |      '-------'
                  |      |         |      .-------.
Gnd   o-----------+------|         |------|Vio reg|---> MCU, SDRAM, flash
                         '---------'      '-------'


[Markello]

Hello All and fzabkar!

I would like to continue this topic, as i have also two dead WD HDDs with fried Smooth chips.
Would someone please be able to provide a pdf for the L7251? there is one easily available for the L7250, but not the 7251.

I want to find out what voltages should be at the test points.

PCBs are the following: 2060-701537-004 rev A
One smooth chip is clearly blown.
Checking the capacitors around the Smooth chips shows that both are shorted.

Spindle motor connectors U V W are all shorted to the ground.

How big is the chance , that main controller is also fried?

Is it even worth to try and replace the smooth chip in the first place?
ROM is located in the 88i8845C-DHG2 controller, so if its fried also then PCB swap is the only option i guess.

Attachments

[Markello]

The preamp gets its +5V supply from the SATA connector, often via a small inductor (for noise filtering). Its negative supply (-5V) comes from an inverting buck regulator powered from the +5V supply, and with PWM control coming from the motor controller.

I was really amazed to find out there are no actual fuses on the 5VDC and 12VDC power rails
Would be a common sense to place two simple fast acting fuses, but no.... There are no fuses at all!

I suspect that the two power rails got shorted together at some point, and 5V power rail received 12 volts, in my case, since two HDDs died at the same time.
These two protective diodes can do very little really.

Attachments

[pepe]

I was really amazed to find out there are no actual fuses on the 5VDC and 12VDC power rails
Would be a common sense to place two simple fast acting fuses, but no.... There are no fuses at all!

there are but some stupid engineer placed them wrong, they actually protect the TVSes instead of the circuit...

if the drives got 12V on the 5V rail, preamp is almost surely toast, so it needs to be properly diagnosed and probably requires head swap in addition to pcb swap... with all the hassle adding to these.

pepe

[fzabkar]

Catastrophic PCB failures:
http://www.hddoracle.com/viewtopic.php?p=5033#p5033

This is what a lot of people do:

Warning: do not interchange modular PSU cables:
http://www.hddoracle.com/viewtopic.php?f=56&t=2545

[Markello]

I was really amazed to find out there are no actual fuses on the 5VDC and 12VDC power rails
Would be a common sense to place two simple fast acting fuses, but no.... There are no fuses at all!

if the drives got 12V on the 5V rail, preamp is almost surely toast, so it needs to be properly diagnosed and probably requires head swap in addition to pcb swap... with all the hassle adding to these.

Thank you for the info.
Well, as suggested, after the pcb swap the platters start to spin up and heads are making the clicking sound for a few seconds, confirming that there is a further problem deep inside.
hdd can bee seen in bios, but identified as another model.

After reading this forum, turns out head swap on WD drives will do nothing in most cases, because of misalignment of the heads., is this correct?

Thanks and Regards

[skinbob]

After reading this forum, turns out head swap on WD drives will do nothing in most cases, because of misalignment of the heads., is this correct?

Thanks and Regards

Not true, I've done thousands of head swaps on WD drives with no issues, its just a case of matching them correctly and having the right tools to do the job without damaging them.

[Markello]

Hi skinbob,

This is from the forum : "Because HSA is not secured internally like other models, instead it is secured by a single screw through the top cover. Because the HSA is not in a fixed position prior to securing it in place the actual alignment can vary. Only after it is secured service and adaptive info is recorded to the surface.

Should the securing screw be removed, whether for repairs or through curiosity, and replaced there is a very high possibility that it will re-align itself to a new position and will be unable to operate, even if the difference in alignment is down to a matter of nanometers."

Few forum users also said that in 99.9% , HSA swap will be unsuccessful in these WD dives. So I am wondering how technician are swapping the HSAs.

[skinbob]

Assuming the model of the drive is the same as the person who created the thread it should be like this:

https://www.youtube.com/watch?v=yzhhKiviYTA

[Markello]

Thank you for the video Skinbob!

Drive I am dealing with is also from WD Caviar Green family, but a different model.

Patient I have is WD10EAVS-22D7B0; 3 platters/6heads, 1Tb.

I was under impression, that head swap on these drives is extremely risky and success rate is extremely low.
Perhaps I am reading too much information.

I do not think i will be doing something like that anyway, as drive does not contain any precious data and extra tools are needed.

[Markello]

Hello All, some update,

I decided to inspect the faulty PCB's further.
Fried SMOOTH chips have been removed, original PCBs inspected carefully, no physical damage found and all shorts disappeared.

Out of curiosity, I decided to transfer chips from the donor PCBs.

Attachments

[Markello]

Surprise! BOTH HDDs showed signs of life!

Clicking sound disappeared, Both drives can now be seen by the Disk Management in Win10.

So clicking sound, after the PCB swap does not always mean that preamp and heads are also damaged.


HDDs have been inside the TrekStore DSDWUB-JM-b enclosure, that also sustained damage.
3,3 volts regulator was gone as well as one 8 pin unknown chip. no marking is visible on it, but it controlled the power button.

3.3V regulator replaced, shorted power button IC removed. Enclosure PCB came back to live!

At this point Win Disk Management can see the HDDs and shows the correct full capacity - 1.8Tb, but disk is not initialized.

I am not in Data Recovery, can someone advice please, what would be the next best approach, to get the data back? or at least to ty to get it back?
What simple programs can be used to restore partitions/files..

Thank and Regards

Attachments