Help identify this mystery A/R-II (solved!)

andrewb

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I recently stumbled upon an A/R-II that I don't recognize as one of the standard versions, and doesn't seem to be documented in any of the popular online resources.

It's a revision A PCB (whereas most of the ones you see tend to be rev J or K), so I'm assuming it's an early design, that maybe evolved into what we have today, however that doesn't make complete sense, when you look at the differences.

The 5V (left) half looks similar to the current design (though I haven't compared every component side by side), however there is a diode in the R29 location instead of the standard 10 ohm resistor. (And I presume there was also one where R30 would be, as the board is marked as such. But it was toast when I got it, and I threw a resistor in there before I noticed it was different).

What's more interesting however, is the right side. The board looks to be a -02 version, as it has +12 and -5V, however the -5 is generated differently than the typical design (which puts the -22V through a 7905 regulator.) This board appears to rectify the 6.3VAC line, then regulate it, and smooth it out with the extra 4700uF cap that's there.

The interesting thing about this method however, is that this would *require* whatever harness this was connected to to provide the 6.3VAC line to J9. And in my (limited) experience, I'm not aware of any games that do that. (And if they did, they would have to require this different design, and therefore require a unique A/R-II that is not one of the documented types.)

So, I'm out of ideas. Can anyone shed any light on this?

Pics below.
 

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How do you figure? The Elektron Forge page says Kangaroo uses a -06, which has no audio.

This board has audio. And that still doesn't address the 6.3VAC issue on J9.

Neither the -06 (nor any other documented version) have traces coming from pins 3 and 6 of J9, which do exist on this PCB, and are routing the 6.3V to the -5V circuit. Those pins are unused on every other version.
 
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It's not an -04 converted to an -02 by chance?

Scott C.
 
Ahh, yes. Thank you Brian!

You can see the layout of the board on page 54 of the service manual, here:

http://pdf.textfiles.com/manuals/ARCADE/SMALLFILENAME/montecarlo.pdf

The giveaways are the big C29, and the two 6.3VAC traces going from J9 down to near C29 (which is why it's not a converted -04, which doesn't have those traces.) The actual PCB layout is different, whereas all of the modern versions use the same basic PCB, but just populate them differently.

Mystery solved. Case closed!
 
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