My Vtech Laser Turbo XT/3 (8086/NEC V30 running at 10mhz) has boot problems and I suspect it has faulty RAM. I've been looking for replacements but there's a mishmash if information out there and I'm trying to make sense of it.

So, the motherboard itself has LH21256-12 chips installed in the slots for conventional memory (640k).

My (Dutch) manual mentions that the motherboard can take 41256 RAM (at least 120 ns) for the integrated Expanded Memory (up to 1 mb). An English manual mentions the same chip but says it has to be at least 150 ns.

This manual from an earlier version of the PC (when it shipped with 512k base memory) suggests that the base 512k can be upgraded to 640k using 4464 (150ns) chips. I found online that 41464 is an equivalent replacement for this. Is that correct?

So my question is: can I use 41256 RAM chips for conventional memory too or is this only suitable for Expanded Memory? Could I also use 4464/41464 chips on my machine?