ARCHIVED FROM - http://www.xs4all.nl/~apronk/gnrpinball.htm
Guns N' Roses Pinball
Welcome at my Guns N' Roses pinball site.
This pinball was made by Guns N' Roses in 1994. If you're
a fan of the band then you probably will like this machine. If you don't
like the music then I strongly advise you not to come near a GNR pinball,
it will irritate the hell out of you. I happen to have a very wide and strange
musical taste, so I don't mind ;-). If you're magnet board keeps blowing
fuses then here may be the solution for you.
Some general info first:
Three flippers, all full size. They are strong flippers and you need them since the left ramp is very steep.
Two Ramps: one is in the shape of an G and the other is in the shape of an R
A Duff Captive ball with a miniature slingshot
Snake Pit (accessible through the G ramp)
A scope in the center of the playfield
Lots of Guns N' Roses music
Three magnets under the playfield
When I bought it, it was supposed to
be in near perfect condition, just like if it came just out of the box. (I
can hear you think "Yeah Right").
If you read my Apollo 13 story, then you know that YOU SHOULD NEVER BELIEVE THAT!
So I didn't. And guess what: I was right (again).
Playfield: wear near the Axl scope all the way down to the slingshots.
Magnets : fuses were blown, thought it was not that bad.
Manual : no! should there be one? YES *@!%$@
I managed to get it for a fair price. I started fixing my magnet board.
I almost died when I saw the underside of the circuit board. Someone tried
to fix it with a blow torch or a "Nuke-it" Zillion Watt soldering iron.
If you want to know what it looked like:
What was wrong:
Unfortunately there is no schematic of the magnet board in my manual. Does anyone have one for me?
My magnet board had some modification for an unknown reason. So I restored it in original condition.
The replacement MOSFET's (IRF540, which are the WRONG types) were all shorted.
I repaired some broken traces and replaced the FET's with the right ones:
IRL540. Unfortunately the IRL540's soon died again and the fuses were blown
too. So, what's wrong? All magnets seemed to work fine in test mode, no problems.
Next step is to enjoy it. The magnets came to life when multiball starts
as they supposed to. Nice.... until suddenly I noticed that they stopped
working. The three fuses were blown and I worried about the IRL540's. They
were ok. So, what's wrong?
I hooked up my oscilloscope on the magnet activation signals. In test mode
there were no problems. All magnets were pulsating correctly. In game I couldn't
detect a problem until I activated some coils. Suddenly the signals went
high, thus activating the magnets, and stay high. The fuses are only 3.15
A slow blows, the voltage on the coils/magnets is about 70 Volts and the
static resistance of the coils is about 4 Ohms. So: if the magnets are continuously
on, the fuses will blow, that's why there should be a pulsating signal on
Tech: side note: Remember Ohms law for static/constant
resistors: I=U/R. So why doesn't the fuse blow? Coils have a dynamic resistance,
starting high and becoming lower and lower. So: it takes some time to build
up a current in the coils: at first the current is low, getting higher and
higher as the resistance drops. Before the current can get to high, the
magnets are shut off and reactivated after a small delay, that's why the
fuses will survive.. This may not be physically correct but you get the idea
End Tech: side note
Now I had to figure out why the magnets were activated when some coils
are activated. I discovered that the static noise that the coils make, affects
the clock signal on the 74HCT273. It 'thinks' that it gets a clock signal
and activates the magnets... leaving them on forever.
The solution: it put a small capacitor of 0.27 uF between the clock signal and the ground. Till now I've had no more problems.
I might make a reproduction of the busted circuit board. I'll post the layouts here when ready. Feel free to e-mail me: firstname.lastname@example.org