Williams: Early Hardware

In my experience, a non-working Williams game usually can be traced back to bad power supply. Of all the Williams games I've owned, every one of them had a power supply problem of one type or another. Most fixes included not only repairing the power supply board, but replacing some of the connectors that loose their spring tension due to overheating, or become corroded.

There are a few good documents on Williams hardware out there.

Things to note: not all parts are the same. Some ROMs boards are strapped for 2532 EPROMs vs 2732 EPROMs. Moving both jumpers on the ROM boards over one position will change the board to accept the other EPROM type. See the conversion articles on wiretap for more details.

Links

Sean Riddle's Williams Arcade Info - Lots of information on the hardware

Williams games and switching power supplies

Since Williams games of this era typically had the problems related to the power supply, most people attempt to "update" the game by putting in a switching power supply to rectify the situation. However, this will, in fact, bring you an entire new set of headaches.

The powering up of Williams games on switching powers supplies can cause High Score Table Reset and Factory Adjustments Restored messages, meaning all your score are now toast, and you are back to factory settings. Very annoying if you had your game set to free play and had your beloved once-in-a-lifetime high score on the machine.

The reason is apparently this: What the game wants is the +5VDC first, then the +12VDC. The +5VDC powers the game CPU, but the game is held in reset until the +12VDC line is fully up. At the same time, the CMOS ram is held in write protect mode by hardware and its contents cannot be corrupted or altered.

The Williams linear power supply has a large electrolytic filter cap across the +12VDC which rises from 0VDC to +12VDC upon power up.

Switching power supplies provide the +5VDC and +12VDC simultaneously, and as such there is little or no reset period or protection for the CMOS ram until the voltages stabilize.

In theory, you could just take a switcher and put a large capacitor across the +12VDC line in order to "slow it down". This does work for some. Another option is installing the original supply. Most problems with the original supply are from 1) connector and header pins needing replaced and resoldered, 2) the large transistor on the heat sink, 3) the bridge rectifier, or 4) the voltage regulator chip (LM723).


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