Roland U-20 - how to replace the battery?

[Motiif]

I recently had my U -20 from the 80's cleaned inside, all contacts replaced and all keys balanced. Shortly after getting it back, the internal battery pooped out and I have no sounds. Battery is a common 2032, got it, took off back, but can't see where battery is.
Tried You-tube, found nothing. Can anyone help?