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Samsung EVO 850 250Gb
http://forum.hddguru.com/viewtopic.php?f=10&t=43699		 Page 1 of 1
Author:  piterk [ September 25th, 2023, 8:41 ]
Post subject:  Samsung EVO 850 250Gb
Hello.

I've seen a lot of forum topics about this Samsung EVO 850 250Gb, but unfortunate nothing close to my problem.

The drive worked smoothly until the very end. The laptop stood running overnight, but unfortunately in the morning I found a message that the system disk was missing.

Upon disassembly, the PCB shows physical damage to the component that exploded as shown in the photo. Is there any point and chance to look for the culprit to fix the drive without losing data.

For a quick
Resistance between ground and 5 volts in and out next to Stef4s fuse
V5 out 2.1v 2M ohm
V5 in - 4.85V 2m ohm
In addition, the Stef4s fuse makes a squeaking sound.

V1 - 1,3mV
V2 - 0
V3 - 0,2mV

ATP4SJ component is heating up.

Sata connector +5 and ground
Pin 4 to Pin 7-9
0.25M ohm

Attachments:
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Author:  Lardman [ September 25th, 2023, 9:07 ]
Post subject:  Re: Samsung EVO 850 250Gb
That's an exploded diode. I believe it's on the boost rail so there should be 12v floating about there somewhere.

V2 is obviously shorted which may be pulling your vout down. Remove the diode for a start at recheck the measurements.
Author:  fzabkar [ September 25th, 2023, 18:42 ]
Post subject:  Re: Samsung EVO 850 250Gb
That 12V boost voltage doesn't seem to be implemented on many SSDs other than Samsung. Micron's Fortis Flash describes Vpp as an optional external supply to improve power efficiency.

Here is a link to a datasheet, but my browser complains about possible malware:

http://am.adianshi.com:6805/%E5%BC%80%E5%8D%A1%E8%BD%AF%E4%BB%B6/%E6%96%87%E6%A1%A3/Micron_L06B_Fortis_Flash_256Gb_512Gb_1Tb_2Tb_4Tb_Async_Sync_NAND_Datasheet.pdf

Virustotal malware scan result on URL:

https://www.virustotal.com/gui/url/51657ba096ef61c084858be5a61eace50c1c09da9037caffa1c1d53f6e8abd28?nocache=1

Wayback Machine:

https://web.archive.org/web/20221206141347/http://am.adianshi.com:6805/%E5%BC%80%E5%8D%A1%E8%BD%AF%E4%BB%B6/%E6%96%87%E6%A1%A3/Micron_L06B_Fortis_Flash_256Gb_512Gb_1Tb_2Tb_4Tb_Async_Sync_NAND_Datasheet.pdf

Quote:
The VPP signal is an optional external high voltage power supply to the device. This high voltage power supply may be used to enhance operations (e.g., improved power efficiency).

This JEDEC standard mentions Vpp several times, but doesn't elaborate on its use:

https://media-www.micron.com/-/media/client/onfi/specs/jesd230d.pdf

If this voltage has taken a hit, then one would have to be concerned about the NAND array, I would think.
Author:  sourcerer [ September 26th, 2023, 5:38 ]
Post subject:  Re: Samsung EVO 850 250Gb
The VPP is the Programming Voltage which is needed for Erasing the flash. Erasing the flash needs a higher voltage than writing to it, and that's what VPP should supply.
Author:  piterk [ September 26th, 2023, 6:07 ]
Post subject:  Re: Samsung EVO 850 250Gb
Lardman wrote:
That's an exploded diode. I believe it's on the boost rail so there should be 12v floating about there somewhere.

V2 is obviously shorted which may be pulling your vout down. Remove the diode for a start at recheck the measurements.


Thanks for the answer. After removing the diode, if I think correctly it was about the damaged component , nothing changes.

So after that i still looking for what going heat so much and it is nearby damaged component on this same circuit. After remove him disk would start and i can copy data from him.

Maybe this will hint at something.
Before the crash, the laptop with the disk kept a little higher temp around 70 degrees. I suspected a cooling problem. However, now after the crash I installed a new drive and the laptop temp dropped significantly to about 48 degrees. So I suspect that the disk must have been heating up already before the crash.

Attachments:
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Author:  Lardman [ September 26th, 2023, 6:31 ]
Post subject:  Re: Samsung EVO 850 250Gb
There's no ground at that inductor to short, if you have data access after removing it then it's likely the short is after it and you've effectively isolated the rest of the rail. IIRC there are only a couple of smaller caps between it and the nands anyway. As long as you have recovered your data - that's all that matters.
Author:  fzabkar [ September 26th, 2023, 13:25 ]
Post subject:  Re: Samsung EVO 850 250Gb
sourcerer wrote:
The VPP is the Programming Voltage which is needed for Erasing the flash. Erasing the flash needs a higher voltage than writing to it, and that's what VPP should supply.

That's the usual case for older storage chips like EPROMs, NOR flash and early NAND flash. However, it's not necessarily the case now. Micron's MLC datasheet.indicates that read performance is improved by 5% or more when Vpp is used.

Quote:
• Array performance

– Single-Plane EXPRESS READ operation time
without/with VPP 64/61μs (TYP) 3

– Single-Plane READ PAGE operation time without/
with VPP 66/63μs (TYP)3

– Multi-Plane READ PAGE operation time without/
with VPP 77/63μs (TYP) 3

– Program page without/with VPP: 1300μs/1225μs
(TYP)
Author:  fzabkar [ September 26th, 2023, 13:38 ]
Post subject:  Re: Samsung EVO 850 250Gb
If you operate the Vpp circuit without the diode, then the inductor's current has nowhere to go when the magnetic field collapses. This will result in very high voltages at the inductor.

Micron's datasheet states that external Vpp can be enabled or disabled via Feature Address 30h. I'm wondering what would happen if the firmware enabled external Vpp but Vpp was not present. Would this degrade the performance of the SSD, or would it kill the performance completely (because the internal Vpp would be switched off)?
Author:  piterk [ September 26th, 2023, 14:04 ]
Post subject:  Re: Samsung EVO 850 250Gb
Lardman wrote:
There's no ground at that inductor to short, if you have data access after removing it then it's likely the short is after it and you've effectively isolated the rest of the rail. IIRC there are only a couple of smaller caps between it and the nands anyway. As long as you have recovered your data - that's all that matters.


This is propably my little bad.
My last answer is to quick and not thoughtful.
When i writen about short to ground i make mistake.

Before removed inductor from pcb all heat very mach. So i try to figure out what element to this. With out thermal cam i put on PCB little bit IPA and watch where is gone first. So it happen on marked inductor so i go to removd it.

fzabkar wrote:
If you operate the Vpp circuit without the diode, then the inductor's current has nowhere to go when the magnetic field collapses. This will result in very high voltages at the inductor.

Micron's datasheet states that external Vpp can be enabled or disabled via Feature Address 30h. I'm wondering what would happen if the firmware enabled external Vpp but Vpp was not present. Would this degrade the performance of the SSD, or would it kill the performance completely (because the internal Vpp would be switched off)?


Now this SSD is only for trash for me or practice with soldering :) So if you want or by interessing i can verify or do some test if you can explain for me what you want.
Author:  fzabkar [ September 26th, 2023, 14:37 ]
Post subject:  Re: Samsung EVO 850 250Gb
Short version:

I would measure the resistance between the cathode of the diode (the striped end) and ground. I expect that there will be a short circuit.

Long version:

I expect that the topology of the 12V boost converter would be something like this:

Code:
                   inductor   diode
                     ___
             Vin o---UUU-+---->|---+---o  Vpp
                         |         |
      .------------------|--.      |
      |                  |  |      |
      |         MOSFET   |  |      |
      |               ||-+  |     ---
PMIC  |   .---.       ||<-  |     ---  capacitor
      |   |PWM| ------||-+  |      |
      |   '---'          |  |      |
      |                  |  |      |
      |                  |  |      |
      '------------------|--'      |
                         |         |
                         '----+----'
                              |
                             ===
                             GND

The PWM controller turns on the MOSFET, and the inductor current then flows from Vin to ground via the MOSFET.

The PWM controller turns off the MOSFET, and the decaying inductor current then charges the capacitor via the diode.

The diode is reverse biased by Vpp during the MOSFET on time.

Of course there is feedback from Vpp back to the PWM controller (not drawn). There would need to be a potential divider on the FB pin to reduce the 12V supply to within the PMIC's Vcc range.

Here is a better explanation:

https://learnabout-electronics.org/PSU/psu32.php
Author:  sourcerer [ September 27th, 2023, 8:18 ]
Post subject:  Re: Samsung EVO 850 250Gb
My guess is that they are using some charge pump or boost converter or something similar internally in the NAND flash chip to boost the voltage, if VPP is not available. This likely saves a lot of stuff from the BOM and space from the PCB. But since charging that charge pump takes some time, it is slower than if they could just use VPP directly and not having to wait for it to be fully charged again. So for SDDs that are supposed to be fast, I would use Vpp and for cheap devices I would go without Vpp.
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