Re: Star Wars Power Supply

True that switchers can introduce their own noise, and there certainly are
unreliable brands out there, but I find the switchers have the one nice
feature of no catastrophic failures. A linear supply can short out the pass
transistor and thus put the unregulated 10.3VDC across the game board. I
have seen this on a Williams pinball game, a Pinbot (I know, I know, but,
hey, the shots are vectors, aren't they?) where the MPU board was
completely destroyed, chips with their tops literally BLOWN off.
Other games that use multiple voltages if one voltage fails, then the RAM
can burn up. So that's why, perhaps for rarest of games, I would recommend
seriously thinking about installing a switcher.

Now, one other good solution might be to get a SCR "Crowbar" circuit and
install it just after the pass transistor. Gottlieb pinballs (vector shots
again!) use this, and I have seen the SCR do it's job a few times over the
years, and protected the logic boards from regulator failures.

If anyone likes that idea I'll post a copy of the (very) simple schematic
on my site.

John :-#)#

At 10:52 AM 8/17/99 -0500, you wrote:
>On Mon, 16 Aug 1999, John Robertson wrote:
>
> > These days it is usually a good idea to replace critical supply voltage
> > with switching power supplies. Computer power supplies are so cheap and
> > reliable, plus they have nice failure modes (they shut down, not short
> > out!). I would have a relay connected to the +12 and use it to disconnect
> > the monitor if the supply goes down.
>
> Here it comes....someone just hit one of my pet peeves....must
>resist.....must resist.......can't resist....
>
> Of course I disagree. Switching supplies, while cheap and
>compact, are noisy (meaning the voltage they produce) and just as
>unreliable. I am looking at literally stacks of old PC cases that our CAD
>department is throwing out due to bad power supplies. Somewhere along the
>line someone got the notion that switchers were more reliable than linear
>power supplies, and that's just not true. It's, of course, true that any
>new power supply is more reliable than an older power supply (just like a
>new car is more reliable than an old car....unless the new car is an
>American car, and the old car is a Mercedes :P ) ...and I think that's
>where that notion came from.
>
> Linear supplies produce quiter voltages, which, leads to, among
>other things, nicer sounding audio when you run amps off of them. No amp
>has an infinite PSRR, so when you hit it with the horrendous supply
>voltages that switchers produce (I'm no expert on switching supplies, but
>I think they switch at around 20 kHz, which gives you nice noise right at
>the "annoying edge" of the audio band) you'll get some distortion.
>
> Not to mention that I'd rather not hack up my Star Wars just to
>put a switcher on the +5V line (I'd have to keep the stock power supply in
>there anyway for the monitor voltages.)
>
>Joe

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Received on Tue Aug 17 11:14:29 1999