We have now reports on newely produced QC8255(T)-based phones (starting from 12W14) are unable to connect using Testpoint.

With 4SE v1.8.2 is not possible to unlock/repair such phones.

4SE - tool 1.8.2
Selected model: Xperia arc S (LT18)
Selected operation: Recovery
Selected replacement of IMEI to: 35850604-xxxxxx-0
Selected interface: USB (BOOTROM)
Checking USB driver status...OK (SEMC Flash Device v2.2.0.5 | 5-4-2010)
Remove battery. Link the TestPoint to GND and then plug USB cable
Connected to USB7
You can now release the keys and allow the process to run. Do not disconnect the phone
Device identification...
Connecting DLOAD...OK (PBL_DownloaderVER1.0)
Sending Preloader...
For now we have reports of LT15, LT18, ST18, MT11, WT19 (EROM: 1241-3656 R9B031) with the problem.

We are checking the information now and searching for a solution. Stay in touch.