Article by Martin Riley

I recently decided to venture into the world of Sega Pinball with an Independence Day.

One of the first things I noticed when giving the back box the once-over was the missing right-hand speaker, and I’m probably not the first person to initially presume it had been removed at some point in its life.

This theory was soon knocked on the head however when I noticed that all the amplifier components for the right-hand channel were also missing on the CPU/Sound board (see area highlighted in yellow below).

The mystery was soon solved after a quick chat with a fellow pinhead who advised that in 1996 (from around Twister onwards), Sega decided to cut costs and remove these items to leave just the left-hand backbox speaker and cabinet speaker (for more detail see Appendix A). Whilst this can be viewed as a not unreasonable idea for sited pins where there tends to be significant background noise, it is noticeable once in the home environment.

As well as the obvious slight imbalance caused by not having a right-hand speaker, it occurred to me that given how Sega sound is stereophonic (unlike Bally/WMS games of the same era which are monaural), then there may also be stereo effects that I’m missing out on. A quick play on an emulated version of the game on Visual Pinball confirmed that there were.

Once I knew this I became a man possessed and set about sourcing the components needed to bring the game back to how it was originally intended to be heard (for more detail on parts see Appendix B).

Populating the board with the components was straightforward (once I’d removed the solder which was blocking all of the holes on the board) and the finished article can be seen below.

Next I had the relatively easy task of removing the blanking plate and installing the right-hand speaker…

…followed by installing the cables to connect the speaker to the Molex connector on the CPU/sound board (highlighted in yellow below)

And the results? Well I think it sounds noticeably better and, despite the speakers being close together, you do notice the stereo effects so I consider it worth the effort and expense for home use.

Appendix A – Sega Sound Generations

Early Sega games up to and including Goldeneye have two backbox speakers and a cabinet speaker, and run in true stereo. i.e. all 3 audio amps are populated on the CPU board.

Mid-life Sega games from Twister through to and including Viper Night Drivin' only had the left hand backbox speaker plus the cabinet speaker and only two of the 3 audio amps are populated on the CPU board.

Late Sega games from Lost in Space onwards have two backbox speakers but they are effectively mono as they are both connected to the left channel audio amp on the CPU board (the right channel amp being unpopulated).

Appendix B – Parts Required and Suppliers

The following is the list of parts which were required. I initially used the values given in the parts list from the manual, but I noticed some discrepancies when double-checking on the board with the existing components on the left channel amp. The schematic in the manual proved far more reliable.

The only place I could find which stocked the heat sink was Mouser Electronics, so I ordered pretty much everything from them apart from the speaker which I ordered from Marco Specialties. Given how well it turned out, it may be worthwhile upgrading the speakers with something like those available from Pinball Pro rather than pairing one new speaker with an old speaker.

Resistors:
R19 (100KΩ ¼W)
R100/102 (22KΩ ¼W)
R101 (470Ω ¼W)
R103 (1Ω ¼W)

Capacitors:
C100 (35V 10µF radial electrolytic)
C101 (25V 22µF radial electrolytic)
C102/104 (25V 100µF radial electrolytic)
C103/105/106/C122* (0.1µF axial ceramic)

* May or may not be present already.

Diodes:
D100/101 (1N4004)

Amplifier:
TDA2030A

Heat sink:
AAVID 531102

Speaker:
4” 4Ω speaker (031-5004-00)**

** Although listed under the Sega item code, the speaker I received from Marco was a substitute and not an original.