I have a WD800JD-75MSA3 drive that suddenly stopped spinning; no reaction when plugged in. I tested the diodes and found that D3 was a short. Sweet! I thought I could remove D3 and cross my fingers to get the drive back. Unfortunately, after removing D3 I tested the diode and it tested normal, so I tested the solder points on the PCB and those are still shorted.

Image here with D3 indicated:


How can I troubleshoot further? I have another identical drive I can use as a reference if needed.

Thanks!

D3 is not a protection diode. You need to put it back.

Measure the voltages at L2, L7 and Q8.

Also measure the voltages at pads 2 and 4 of the HDA connector (J1).

_________________
A backup a day keeps DR away.

Thanks for the reply! I thought it was strange that the diodes were so far from the power connector. I'll put it back

To be clear, you asked to measure voltages, so should I provide power to the PCB while detached from the HDA? Should I put my black lead on a common ground (like pin 4, 5, 6 of the SATA power connector) and red lead on those points you mentioned while powered up, or should I measure across the components (That is, should I voltage reading from L2a to L2b, L7a to L7b, Q8 to each of the C, B, E leads, and Pad 2 to Pad 4)?

Or should I just measure the resistance of these components?

Thanks again

Connect the black lead to a SATA ground or screw hole, and then measure the test points with the red lead.

BTW, it looks like the Marvell MCU has a black mark over the "M". Is that a burn mark, or is it a piece of foam?

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A backup a day keeps DR away.

<cough> J1 </cough>

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Data Recovery Services in the UK.
https://www.usbrecovery.co.uk/

MCU looks toasted

Not neccessarily, it can be a piece of foam (as Franc supposed), just as what's visible above the RAM pins.


It is not spinning, which can't be due to that.

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Adatmentés - Data recovery

That's just foam.


Thanks, I missed it the first time. I see it now

Your suggestion was to measure voltages, but I was scared to test with a PSU attached so I tested continuity first. I have a same model drive so I was able to compare to a known good drive:



I actually tested them both again and got OL on Pad 2 for both drives, so I'm not sure why I got different readings the first time. However, L2 is shorted on the drive that won't spin up versus 98Ω on the good drive.

L7 is part of the negative supply for the preamp. It is normally grounded at one end, so your reading is OK.

L2 is part of the Vcore supply for the MCU. You are actually measuring the resistance of the MCU core at this point. A reading of ~100 ohms is normal, but your reading of 11 ohms would suggest that the MCU is dead. :-(

Did diode D3 test the same as L2 in-circuit? Did you power up the PCB after removing the diode? D3 is the flywheel diode for the Vcore supply. When the MOSFET (6-pin device) switches off, the current in L2 is suddenly interrupted. D3 allows this current to decay gradually. However, if D3 is absent, then a very large voltage can appear across L2, potentially destroying other components.

_________________
A backup a day keeps DR away.

Thanks for the help.

I can't remember exactly what D3 tested when I had it out of the board, but I think it was between 100 and 300 ohms.

I did power up the PCB when I had D3 removed (because at that point I thought it was a TVS diode \facepalm), so it's possible I've done more damage to other components than the possible dead MCU.

FWIW, I do have 2 similar HDDs with matching firmware (See attached photo; Failed drive on the left, two known good drives on the right). Is this 15 year old drive a candidate for a straight up PCB swap or is it the type that has unique programming? Will I harm anything if I try?

I'm asking whether you tested D3 in-circuit before you removed it. This will tell us if you caused the fault in the MCU, or whether it was already present.

This site says that a U12 swap is necessary:

https://www.hdd-parts.com/14101994.html

_________________
A backup a day keeps DR away.

I was highlighting the OP's J1 and J6 confusion when asked to take voltage readings, not the fault itself. I should have been clearer.

_________________
Data Recovery Services in the UK.
https://www.usbrecovery.co.uk/

I had tested D3 in-circuit, and it was reading as shorted. However, after removing it I discovered that the short was not in the diode but in the board. When removed, the diode reads 243 ohm (good boards read 100 and 134 in-circuit). When the diode is still removed, the empty terminals read as a short. Good boards show a short between ground and the right terminal, but ground to the left terminal reads the same as the diode's resistance (as expected).

This means that before I did anything to the board, there was already a short across the terminals where D3 was connected, bypassing the diode. So it sounds like the good news is that my powering up the drive with that diode removed didn't do any more damage than was already done, and the bad news is that the damage was already done.

In any rate, your link to hdd-parts makes it sound like I can remove the U12 bios chip and put that on one of my known good donor boards and use that on this HDA to get it working again. Alternatively I could pay them $50 to do that for me with one of their boards. Unless there's a chance U12 is damaged, at which point I'm S.O.L.?

Just wanted to update, I was able to move U12 to a donor board and everything came back up (albeit a little slowly). Thanks for the help everyone!