Namco ‘CUS99’ reproduction

The ‘CUS99′ (simply silkscreened ’99’) is a custom IC used on Namco arcade PCBs.It’s a 16 pin SIL component covered with a brownish coating :

It can be found on pre-System86 (Pac-land, Sky Kid, Gaplus, Dragon Buster and other boards..), System86 (Rolling Thunder and other games on same PCB layout) and System 1 hardware.From the scarce info about it the ‘CUS99’ is involved in sound volume control but we knew nothing more detailed about, pinout from official schematics apart :

Recently I’ve been sent by the user ‘JorgePT’ a pile of System 1 boards for repair hence, with his permission, I analyzed the part. After drawing schematics of its internal structure I came to the conclusion that the ‘CUS99’ is nothing more than a 4-bit DAC with output level control performed by analog switches.Its design was quite simple and easy to reproduce with few parts  :

Testing of the repro on a Pac-Land PCB was successful:

Thanks again to ‘JorgePT’ for his willingness.