Help with HDD PCB Component?

[myfirstpost]

Hello,

I'm wondering if anyone can help me determine what this component is (or more importantly what a tolerable replacement would be). It's by Fairchild and has the markings:

P54AY
2011
C

I fried a Seagate SATA HDD by hooking up my PSU wrong. Removed the 5v TVS and it spun up, but kept clicking and wasn't recognized. This component was getting really hot and was (I believe) causing a short.

Searching around the internet/the forums I found a document from fzabkar (http://www.users.on.net/~fzabkar/HDD/HDD_ICs.txt) with the only close in name component (P52AB), and I think suggested it was an LDO regulator.

However, I'm a little lost on the specifications I would need for a replacement. I do have a very similar (working) PCB with a very similar component, but I have no idea how to test/find the values I'd need.

Any help would be greatly appreciated. Just lurking this forum has been very illuminating!

Attachments

[pepe]

Hello,

you probably fried the preamp with 12V on the 5V power line. A pcb swap or repair will not help in such case, even worse, the dead preamp can easily carve your data off the surfaces. Time to contact a pro ...
pepe

[fzabkar]

99% of "pros" would transfer the "ROM" (25P05VF) to a replacement PCB and simply power up the drive. They wouldn't know how to check a preamp.

As for the two chips, I can't understand how the board is able to spin up the drive if either chip is dead. These chips appear to be the buck converters for the Vcore and Vio switchmode supplies. Vcore would be 1.2V while Vio would be 2.5V or 3.3V. You can measure these voltages at the coil or across the filter capacitors. If you suspect a short circuit, measure the resistance across the capacitors.

[pepe]

Look, he removed the TVSes, drive spins up but clicking. What would convince you about preamp being dead or at least with 90% probability?

No further DIY checks are recommended if the data is important on the drive.

the 99% assumption is pretty steep as well, and even if that would be the case, is that a reason to suggest more tests which can cause more damage to the data?????

If there's a safe way, why not take that?

pepe

[myfirstpost]

My apologies, I should have specified the data is not important. (There is none)

Is that allowed here? Just trying to learn.

I'm aware I may be attempting something futile, and thus not expecting anyone's help, merely asking.

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You'll have to bare with me, as my knowledge of EE is somewhat limited/superficial. I have a vague practical understanding of how to get certain things working, but don't fully understand the fundamentals/vocabulary.

My troubleshooting procedure has been as follows:

- Removed TVS diode, attempted install. Drive spins but clicks and isn't recognized.

- My understanding is removing TVS diode would create an open circuit between TVS diode pads, where instead I measured about 50 ohms resistance.

- Plugged in PCB and the two chips in question became quite hot.

- After disconnecting power, checking continuity I found small resistance values between ground and 5v rail.

- Removed the two chips and now the TVS diode pads read open circuit. However, at the now empty pads I read a small resistance between what I believe is the ground pin and the 3.3v/1.2v output pin. (I tested these devices on the other similar good board and they do show 3.3v on the top right one, and 1.2v on the other)

- See photos. On the good board, pin 6 is 1.25v and 3.3v on the left and right chip respectively. (I measured the voltage on the bad board earlier, but can't remember values before I took them off. I think it was 1.25v on the left chip and 5v on the right.)

- As you can see from the photo I've been trying randomly and haphazardly to isolate the short by removing components, to obviously no avail.

- A brief note, these small resistance values I measure seem to vary depending on how hot/cold the board is. After removing components (hot air station) it went down to 16~ ohms and after throwing it in the fridge it it went up to 200~

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I know I'm an idiot, but is there any likelihood I'd isolate the problem if I, say removed every visible component? (Save the RAM, MCU, and motor controller)

Or is it some internal trace that might be broken?

- Oh and in regards to the preamp, I swapped out the board with the similar one and the drive spun up with no clicking noise (or any other painful sounds). Would this imply the preamp is OK?

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[fzabkar]

@pepe, I understand what you are saying about the preamp. If it fails in such a way that a head's write element is always switched on, then the head can write all over the disc. This can not only damage the data, but also the SA and servo information. I do remember that thread where you first proposed this, but ISTR that most people considered this to be an unlikely scenario and so would not be bothered to test for it, even if they knew how.

My observation of the OP's predicament leads me to ask how it was that the OP was able to spin the drive with a PCB where one of the regulator ICs was visibly damaged. I can only theorise that one or both of the regulators had developed a short between input and output, in which case the relevant supply would have sent the full Vcc into its load. I recall a thread involving a Seagate Grenada (?) PCB where one of the regulators failed. The OP in that thread substituted a home made linear regulator. He initially miscalculated the output voltage, causing the MCU to be greatly overvolted. The drive still spun up, but it filled the terminal with servo fails. After the OP corrected his error, the drive came good and he was able to recover all his data.

In short, I'm wondering whether a high Vcore or Vio supply might allow the PCB to spin, but play havoc with the preamp or read channel.

[fzabkar]

- Oh and in regards to the preamp, I swapped out the board with the similar one and the drive spun up with no clicking noise (or any other painful sounds). Would this imply the preamp is OK?

It sounds promising. Try transplanting the "ROM" chip to your donor PCB.

I suspect that your faulty Vio supply (5V instead of 3.3V) may have been responsible for the clicking, possibly via a misbehaving read channel inside the MCU chip.

[pepe]

I stand corrected, i missed noticing that spot on that regulator. And yes, that's most probably the one creating -5V for the preamp (not creating in this case).
So yes, it looks like the preamp is OK and you can get it going by swapping the serial flash (right in the middle of your very first pic).

pepe

[fzabkar]

I stand corrected, i missed noticing that spot on that regulator. And yes, that's most probably the one creating -5V for the preamp (not creating in this case).

No, those two regulators produce Vcore and Vio, as the OP has already confirmed.

The -5V supply is produced by the coil and E3P1S IC (FETKY ?).

[pepe]

You are right again the traces go to the MCU. Then it is quite strange how it can spin up without Vcore or Vio. I am starting to be curious...
If it is Vio, all circuitry that requires this supply is supposed to be dead, including the serial flash interface, the spindle controller interface and preamp interface too. The first two is critical for spinning up unless it has internal ROM as well, from which it can boot up, but in this case it still has to talk to the spindle controller which requires Vio, at least that's what i would think. I guess it might be shorted or low resistance, thus, being a buck controller, providing some voltage on Vio, so that some things are able to work.
However, if the Spindle controller can be driven from it, why not the preamp?
The question is wether it spins up with that burnt IC removed?
I could not see a reference to that in the OPs long post.

pepe

[pepe]

edit: reading that post a bit more thoroughly i found that there was low resistance between 5Vin and GND when the small chips were in place, and this went open when he removed them. This leads me to the conclusion that the chips are shorted, ie, driving Vio and Vcore with a large voltage, which caused those circuits to malfunction and something went almost shorted (50ohm).
Anyway, if there is a replacement board available i see not much point in swapping any ICs other than the ROM and get on with the good board.
pepe

[fzabkar]

@myfirstpost, you might find this tutorial useful:

Tutorial - Linear and Switchmode Regulators used in HDDs:
http://www.hddoracle.com/viewtopic.php?f=59&t=231