Now.....there's a "dilema"....well not really.
The thing is that, long time ago, before I even owned the Meteor or Asterock, I had the opportunity to buy an untested Asteroids PCB for a very nice price. I took a chance, and when I brought it with me to Speleo on our first visit to him, I asked if he could test it on his Asteroids cocktail.
He first gave it a good visual inspection and then asked me where I got it from....I told him, and he said that he had repaired that very board earlier !!!
And indeed it was working 100%
So....now....since I really do not like the fire sound (the "new" Atari speaker made it a tiny bit better, but it's still annoying as hell) and I really mis the fire sound of the saucers I was thinking about using the original Asteroids PCB in the Asterock. Of course this had to be a 100% reversible solution... (By the way, there is another BIG reason for wanting to run an original Asteroids PCB, and that is the (hopefully soon available) Asteroids 3in1 kit that has Asteroids, AD AND Lunar Lander (!!!) on it...plus of course extra's like free play and hi-score saving....
So, the first thing you check if you want to do this, is of course check if the Sidam PCB might be pin-compatible.
Checking out the schematics soon indicated that although both have 22 pins per side, they are completely different.
And not only that, there were even some "major" differences in the electronics.
The fist one was the handling of the buttons and coin-mech switches etc. Almost EVERY game around, has inputs for those switches and you need to short (close) them to ground to activate the input. In a (futile) try to make Asterock "different" from the original, Sidam decided to let all the switches be operated by putting a +23V signal on them. Yes I couldn't really believe it at first either, but it's true..
Now...this would mean a major problem of course. Would I have to "invert/convert" that signal or make other changes to the PCB, I really didn't want that. SOoooo, I checked the manual again, and the solution turned out to be very simple. The +23V is a "shared" line that runs to all the contacts. Sooo, if I would connect GND to that line instead of the +23V it should simply work !
The second problem is that Astroids "wants" 36VAC on two pins. On the game PCB that voltage is rectified to DC using a diode bridge and filtered with a cap. This results in about +22V and -22V, which are fed to 78xx and 79xx voltage regulators to create various voltages for (amongst others) the vector DAC's.
Now...the Sidam engineers decided this was something that belonged on the Power Supply section (and I agree) so they put the rectifiers and filter cab on the PSU and so instead of +36VAC, +23V and -23V (never mind the 1 voltage difference, it's unregulated anyway) onto the game PCB...
So....instead of having 36 VAC available, I have +23V and -23V available. But wait a minute I need that voltage right behind the bridge rectifier
on the Asteroids PCB !!
So....should I make bypasses ? No, please NO modifications to either the harness or PCB....
Mmmm, than I thought about how some people "hack" a DC voltage PSU to f.i. Galaxian or Pac Man PCB's.....they simple connect it to the AC inputs ! And I thought this should also be possible in this situation.
Why this (should !) work ?
Well...check the schematics again:
Of course the Asteroids PCB "expects" AC on the inputs, but if I connect the +23VDC to pin X, and -23VDC on pin 20 it should simply work.
From x, the + voltage will go through CR11 and hey, there is where we need +22VDC ! (Green arrow).
The diode actually helps lowering the voltage a little bit, so we should be safe !
Also, the + voltage from pin X should be BLOCKED by CR10, so that's safe too. (Red Arrow)
On the other side, the -23VDC should be passing through CR9, while being blocked by CR12, so we'd have -23VDC on the 7915 input too.
(I didn't draw arrows for this, to keep things clear, but it works the same, but reversed as described above...)
The caps simple provide a little bit of extra filtering which never harms
So in theory I think this should work great .....(if someone sees a reason why it shouldn't, please give a shout !
So....in the end.....all I have to do is make an adapter ! Great !!!
I made a little table with what goes to what....now all I need to do is build it !
