Long ago in a space far, far away, the Quelab crew had a means of amusement: Asteroids.
A donation from Adric, the Asteroids cabinet has seen its fair share of hands across its buttons: life at, presumably, an arcade and then later at Southwest Cyberport, it was brought to Quelab after it just didn’t have any more go in it. Never one to give up, we replaced the required parts, added a high score save kit, and pounded out more hours on it, racking up high scores in the 15,000 range. Some time later, we moved, and the cabinet stayed dormant: Nobody really wanted to play it much anymore. The buttons had been abused and left in a sorried state, dust had crept in, and the final straw came when a known issue with contact corrosion had made the board unable to boot again.
That is, until someone decided to fix it. Morgan G. (myself) and Ben L (of Black Lodge Research in Redmond, WA) decided to dig in and, over a weekend, get the thing up and going properly. Some preliminary work had gone into getting it working again.
So, what needed to happen? Just some cleanup, love, and a bit of attention. New fuses, cleaned contacts, and lots of reading schematics later made it clear what the problem was, and some new features we could add in for fun, and a beautiful, well-loved cabinet was given new life.
We left a note to anyone who opens the cabinet up in the future, as well as a copy of the manual, reproduced in true Atari form, plus some spare parts.
The root cause of the cabinet not working is a well-documented flaw in power supplies that use a sense line: the sense line needs to be really good in order for the whole thing to work, and if it isn’t, there’s a good chance the PSU will just cause problems. In an ideal world, they’re self-regulating; From an EDN article on the topic:
The remote sense function automatically increases the output voltage at the output terminals of the supply to compensate for any unwanted voltage drop in the output cables with heavy load currents. Likewise, the remote sense function decreases the output voltage of the supply when the required load current is reduced. In some applications, the power supply’s output needs to be adjusted by the user to voltage higher than its nominal (e.g. 5V nominal, adjusted to 5.5V). Always adjust the power supply’s output while measuring the voltage at the load.
The EDN article concludes saying these are only really useful in extremely high load environments (read: not the environment that Atari had been building for) and should be avoided in newer designs. Perfectly reasonable in Atari’s days, but we’ve learned new things about how the world works. It’s bad enough that bypass hardware exists for these since a bad sense line can cause insane voltages (40-80V!) when they go bad.