Bubble Bobble repair log and 'PS4' custom MCU reproduction

Who among you does not know and has never played Bubble Bobble in his arcade life? Personally I love this game and I was looking for an original board since ages but never been lucky to get one so I always ended up settling for bootlegs.But recently I spotted on eBay a legit PCB from Taito.The description said the board was in good condition but not working due to missing security chip.Despite this I made some bids and won the auction (final price was not really cheap though...).When I received the board there were no surprises to me, the chip @IC17 on top board was missing hence the PCB was dead :

 This chip is, indeed, the custom MCU with Bub silkscreening, here's a picture of it found on the net:

Some years ago this chip has been decapped and internal ROM extracted improving the MAME emulation that used a simulation of the chip behaviour until that moment.You can read more about on the blog of Nicola Salmoria (the original developer of MAME)

http://mamelife.blogspot.com/2006/08/good-news.html

http://mamelife.blogspot.com/2006/08/completed-at-last.html

Thanks to this brilliant work we know now that the Taito 'PS4' custom IC is a Motorola 6801U4 MCU in disguise with some additional features.Since the internal ROM was dumped the only chance to repair my board was to get a chip and program it with MAME dump.Sadly I found no MC6801U4 around but only MC68701U4 which is pin to pin compatible.The chip arrived and thanks to one of my programmers I was able to program it with the file in the MAME ROM set :

With MCU installed the PCB came back to life, the game was fully playable with sound but some parts of graphics were wrong or missing :

 

 

All the graphics are generated by the bottom video board :

 Data are stored in 12 27256 EPROMs :

 

I dumped all of them and did a compare with MAME, two files were unknown as they didn't match any existing ROM sets :

 

 Trying the bad dumps in MAME exactly reproduced the board issue :

Reprogramming two blank EPROMs fixed the graphics.Playing some games I noticed the sound was quiet also on highest volume setting , I fixed this issue by fully recapping the sound section :

The repair was now complete, board was 100% working but I thought that solution to replace the 'PS4' custom MCU with a MC6801U/MC68701U4 was not accessible to everyone because very few programmer supports this obsolete device.So, I looked for another solution and found that some bootlegs use a little sub-board with a different MCU and some glue logics as replacement of the 'PS4' custom IC.I managed to find such bootleg and did a modern reproduction of this replacement, it worked fine when I tested it :

 

 

Another successful repair and another custom IC preserved!