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 Post subject: Re: Hitachi 2.5" 250GB suddenly stopped spinning
PostPosted: April 14th, 2019, 15:09 
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Joined: November 22nd, 2017, 21:47
Posts: 289
Location: France
With no current, if the multimeter is set to Ohm / 200, I get 130.0 to 130.4. If set to Ohm / 2000, I get 165 to 168. If set to Ohm / 20k, I get 0.42. Seems weird. Measuring again a few minutes later, now I get about 124.0 / 158 / 0.39... then a bit later, ~118.0 / 150 / 0.37... :shock:
What would be the expected value ?

I still don't know for sure if the ROM chip is the one in U6.


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 Post subject: Re: Hitachi 2.5" 250GB suddenly stopped spinning
PostPosted: April 14th, 2019, 18:13 
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Joined: September 8th, 2009, 18:21
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Location: Australia
The diode is probably OK. Can you measure the resistances between ground and each of Va, Vb, and Vcore?

I suspect that U6 is the NVRAM. The unpopulated location at U3 is probably reserved for the ROM, so this would suggest that the ROM code is embedded within the MCU. Can you tell us the markings on U6?

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 Post subject: Re: Hitachi 2.5" 250GB suddenly stopped spinning
PostPosted: April 14th, 2019, 20:53 
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Joined: November 22nd, 2017, 21:47
Posts: 289
Location: France
Quote:
The diode is probably OK.

Wasn't that established based on the fact that plugging the drive internally did not cause the PSU to shutdown ?
(By the way, is this rule also true when plugging the drive through a USB adaptor ? Does a shorted diode shut down the adaptor's power supply ?)

Quote:
Can you measure the resistances between ground and each of Va, Vb, and Vcore?

With the multimeter set to Ohm / 2000 : Va = 1152-1153 / Vcore = 325-355 (again it seems to be going down with each subsequent measurement) / Vb = “1 ”, but 10.68 if set to Ohm / 20k -- that would mean 10680 Ohms, right ? (as it may be quite apparent I barely know what I'm doing here ! :) I'm almost completely illiterate on the purely electronic side of HDD related things...)

Quote:
I suspect... is probably... this would suggest...

So it's not even something standard and easily recognized with a bit of experience ? You have to do the guesswork for every single drive model ? :shock:

Quote:
The unpopulated location at U3 is probably reserved for the ROM, so this would suggest that the ROM code is embedded within the MCU.

Which would mean that dumping the code with advanced software tools is required, right ? But is that even possible if the PCB doesn't register any status, as per the tests I made with Victoria / WDC Marvel ?

Quote:
Can you tell us the markings on U6?

Very small and hard to read, but most likely “C66WP / KB44” :
Attachment:
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SAM_2490 détail.jpg [ 61.29 KiB | Viewed 1573 times ]


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 Post subject: Re: Hitachi 2.5" 250GB suddenly stopped spinning
PostPosted: April 14th, 2019, 22:37 
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Joined: September 8th, 2009, 18:21
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Location: Australia
U6 is a 93C66 NVRAM. The ROM is embedded in the MCU. Therefore you would first need to find a replacement PCB with the same ROM firmware, and then transfer the NVRAM.

That said, there are no short circuits at your Vcore and Vio supplies, so it may be that the fuse is open circuit due to "fatigue" rather than an actual fault. You could try replacing the fuse, or bridging it (risky). Hopefully that's all that you need to do. Otherwise, try to find a PCB with matching firmware.

BTW, the reason that a shorted diode would not have shut down your PSU is that the open fuse disconnects the entire PCB, including the diode, from the supply.

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 Post subject: Re: Hitachi 2.5" 250GB suddenly stopped spinning
PostPosted: May 3rd, 2019, 17:50 
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Joined: November 22nd, 2017, 21:47
Posts: 289
Location: France
Quote:
U6 is a 93C66 NVRAM. The ROM is embedded in the MCU. Therefore you would first need to find a replacement PCB with the same ROM firmware, and then transfer the NVRAM.

What is the exact role of NVRAM ? Isn't RAM supposed to be a volatile kind of memory ?

Quote:
That said, there are no short circuits at your Vcore and Vio supplies, so it may be that the fuse is open circuit due to "fatigue" rather than an actual fault. You could try replacing the fuse, or bridging it (risky). Hopefully that's all that you need to do. Otherwise, try to find a PCB with matching firmware.

Is it something that is known to happen with old HDDs ? It's strange in the sense that the fuse is supposed to protect, but if that is indeed the case it would be the direct cause of the failure... “Same thing that helps you live can kill you in the end”, as Neil Young sings.
Or could it have been a short circuit due to the way the drive was plugged ? I'm not certain, but when the failure happened it may have been lying directly on top of a 3.5" HDD (itself unplugged), plugged through a SATA-to-USB board with no plastic protection, which I realize now might be a very bad idea...
Bridging means simply soldering a small wire on each side, correct ? Is it risky even if the power supply is perfectly stable ? (I do have a UPS.)
According to “Spildit”, the odds of success for this kind of repair procedure are low with Hitachi drives in particular, do you have similar experiences ?
As for replacing that fuse, where can I find one, short of getting a similar PCB just for that purpose ? I doubt I could find that tiny thing in a regular electronic shop.
And as for a PCB with a matching firmware, isn't that a fool's errand, based on the “adaptive” data which supposedly is also embedded in the ROM code ?

Thanks again, and sorry for those long delays between replies, as I have more urgent matters to deal with right now (cat related in particular – my poor lady has had breast cancer for three years, and it's getting really hard to find a fix at this point...).


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