Movement replacement for a Seiko 7T42-6A5A

[hansevin]

Hi Everyone,

I'm looking at replacing the movement for this model. After some searching I've managed to find a replacement movement (part: 7T42B), but I can also see that there does exist another variant of said movement (part: 7T42A).

I apologise if this is a silly question but is there any difference to these movements (variants A & B) or are they interchangeable? 

I've downloaded both manuals for the A & B variants and their sizing tolerances (outside diameter, casing diameter, height) are identical barring a few internal components. Again I apologise if this is a silly question, the movement itself is quite pricey and I don't want to be left with an unusable part.

Any clarification would be greatly appreciated!

Cheers.

Edited April 1, 2022 by hansevin

[xyzzy]

You should be able to tell which it had originally, as it says on the movement.  They should both fit the same spacer rings and cases.

Keep in mind that there are two different hand height versions of these movements  The center wheel, hour wheel, and sweep second wheel are different.

Is the watch an old one, 1988-1989?  I think Seiko switched from the the A and B around then.  6A5A looks like an old model, so it might have had a 7T42A.