How many 'Issued' board?

[100monkeys]

How many 'Issued' boards were manufactured in the life of the ZX81?

I have only seen 'ISSUE1'and 'ISSUE3'
I don't really know what my first one was (about 26 years ago?)
I don't really know what i did with it, probably gave it away, good ol me heheh.
I moved to APPLE][ after that (via a BBC/ACORN)

But now i am at an of 'retro prone' age i have both the ISS1 and ISS2

There is an obvious difference between the 2.
But, could i use an ISS3 ULA to repair an older ISS1 board?

Regards

[BrunoFlorindo]

I don't know the answer to this question. Anyone? It's sad that he didn't get a reply when he made the question.