Trying to find details of "the main chip".... ironically one of my top Google hits was this very project on HackADay. :/

I've found a Chinese reseller that's selling "the main chip" https://www.jotrin.com/product/parts/LA_180D so, at least, we now know it's designation.

There was a promise of a datasheet at the above address but after they got me to create an account (probably just a way to obtain my E. mail address for spamming), The promised datasheet link just takes you to Panasonic's website.

But at least now we know that it's a Sanyo LA-180D. Although http://www.showadenshisangyo.co.jp/import_csv/stocks/10001-450.html seems to think it was manufactured by Oki.