It sounds awfully like the terminal is connected to the safe mode pins to me.

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I'm re-reading the conversation, if he is shorting the 2 pins next to JTAG that's safe mode, the next two pins are UART.

Let's hear what he says.

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I found 3 caps where the measured resistance is 0 ohm. See the attached pics including the UART. The 2x caps are on the other side of the controller chip. Here are the voltages I measured on the connector for the very first time.
Starting from the bottom JTAG pin in the pic. 0v 2v 2v 2v 2v ... 2v 2v .. 0v 2v ( tiny ones 1mm )

Initially, I thought the 2 pins next to the JTAG are "safe access" pins, shorted those but it didn't do anything so I thought but then I didn't have working UART. So not sure if it helped in anyway or maybe that's why I could see drive capacity at least while connoted via USB enclosure? I don't know. However Knowing the voltages and per the Missingmanual guide, I concluded that the top tiny ones are "safe mode". Later on shorting those would make the disk not detected in "diskmgr" and removing the short, would make it detectable.

Not sure if I short something on my second try to measure the voltages with another DMM. I never used the VCC pin of the USB adapter used for the UART.

ISTM that you have mixed up the UART and Safe Mode pairs. The pair closest to the JTAG pads is Safe Mode. At least that would be consistent with Ace's video and @sourcerer's manual (even though they are different models). Shorting the UART pads should do no harm, though, if they are indeed the UART. In fact, those two smaller pads may not be UART pads. One appears to be connected to ground.

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I just popped open a 120gb 850 evo I bought for r&d. Just to be difficult the layout is completely different, but I have confirmed the 2 smaller pads (mine are underneath) are definitely safe mode which are the ones silcontool has marked as such.

I'll have a poke around for terminal when I get 5 mins.

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That would make sense. One pad would be grounded, the other would be pulled up to the Vio supply via a resistor.

Hopefully those other two pads are connected the controller's GPIO pins and not to a supply rail.

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I hooked terminal up to the extra pads and got nothing even with an added earth bond in case it was floating, thought it might be the cheap uart at first but get equally nothing using the ace adapter. The drive here is fine, and still working despite me fumbling about with the adapters set from 1.8v to 5v so I assume the OP's wont have suffered either.

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uart is not routed out to those pins as far as i remember.

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I couldn't be sure I'd found it, I found a candidate pad for TX using the meter after scratching away some coating on the back below the crystal but without something like jtagulartor I can't confirm.

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@silcontool", are either of those "UART" pins next to the JTAG row grounded or shorted to ground?

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No. Neither of the 2 pins is grounded. Both pins have +1.87V on them.

Then I guess your drive has failed coincidentally, not because of any user error. I don't know which tools or skills you have, but you would need to determine whether any of those 3 capacitors is responsible for the short, or whether the load switch IC itself is shorted to ground. If it's anything else, then I don't know.

One way to locate the short would be to check the temperature of each cap to see if it getting hot (a finger test may suffice). A better way would be to remove them one by one and retest the circuit for shorts.

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I'm going to buy another 850 EVO ssd to compare with and help figuring out a probable cause of the trouble.

Any suggestions for tools I must have would be appreciated. Thanks

I am not aware of any DIY tools to fix firmware problems in Samsung SSDs.

At the moment you have a hardware problem that is relatively simple. Ideally you would use a hot air station to remove the caps and possibly the load switch. However, even if you resolve the hardware problem, you will then be back to the original firmware problem.

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