I have a ST1000LM014 that has the signs of a corrupted NAND, I'm going to follow the steps outlined in other threads on how to reinitialise it.

But I need a TTL adapter that can communicate with it. I've got a CP210x that works fine with other Seagate models, but it wouldn't give any terminal response with this drive.

I've also tried with a PL-2303HXD, that would give a terminal response, but its just all random characters.

In this thread
https://forum.hddguru.com/viewtopic.php?f=1&t=26917
the OP seems to use PL-2303 but has done some serious hacks to get it working. But he confirms that the standard config of 38400 speed, 8 data bits, no parity, one stop bit, no flow control is what it should be set to.

The voltage on the Tx and Rx pins of the drive measure 1.8v. Both those TTLs are supposed to operate at that range, but something is going wrong.

Does anyone know of a specific TTL adapter that will work here?

Could it be that the PL-2303HXD does work ok normally but the corrupted NAND is preventing a correct read out?

Problem likely isn't your TTL adapter. Some drives just have the terminal locked out until initialization is complete.

Even if you could TTL in, the diagnostic port is likely locked.

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Data Medics - Hard Drive, SSD, and RAID Data Recovery Service Company

This is Kahuna series which does not have locked ROM, but if NAND is bad then even with terminal access you will never reach a required prompt from which you can enter serial commands unless you can patch it, but if you had the equipment and knowledge to do this then you would not be here asking this.

If it is data you need, then consult someone who can help you safely. If it is curiosity, then you would need at least a donor PCB with a functional NAND but simply transferring ROM chip alone will not help with this series of drive

@jordash, you need to initialise the NAND flash IC.

See viewtopic.php?f=1&t=35895

Your adapter cannot communicate with a 1.8V UART. It needs to be modified so that its I/O logic is powered from a 1.8V supply rather than the chip's internal 3.3V LDO regulator.

Alternatively, you could try this Kindle patch:
viewtopic.php?f=1&t=29286

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A backup a day keeps DR away.

Thanks for the replies, I was going to try to confirm my TTL would communicate with these drives before I bought a donor. But seeing it wouldn't get a terminal read out with a corrupt NAND, I'll buy a donor and see how I go with it. I'll update on progress.