Trying to restore modified Major Havoc board

Hello,

I just picked up a Major Havoc board w/ Tempest adaptor. I installed
it into my Tempest cabinet but things are definitely not right. I
used to own a MH Tempest conversion, so I'm quite familiar with how it
is supposed to behave. And yes, before I even connected it, I flipped
the smaller connector.

Based on the main symptom, which was that all the vectors were drawn
short, and the fact that there is a 12.096MHz crystal on the board, I
figured out that someone has modified it for use with an Amplifone.
It's definitely a conversion board, with the jumpered pins on the
small connector and a serial number starting with CK. In fact both
crystals (a 12.096MHz and 10MHz) have been soldered to clipped leads
of previous crystals.

The next thing that is wrong with it, is that half of the sound is not
working. To be more specific, it sounds like some voices are missing.
 Most of the sounds that do play are explosions, and the theme music
at the beginning is only the lower "instrument". Even the explosions
don't sound right though, like they are only partially playing. The
board has a real Quad-Pokey, not an eliminator board… I don't know if
this was normal for conversion boards, but my old one had the
eliminator daughter board.

The display has pincushioning going on, even though the adaptor looks
fine. I can't imagine why. I also found that when I first
installed the boards I had to turn up the brightness on the monitor
significantly, and if I turn it up too much the retrace dot in the
center is red, rather than white. Not sure if that means anything but
I found it odd.

My Tempest spinner does absolutely nothing with MH installed, but it
works perfectly with Tempest. The person I bough this from said his
Tempest spinner worked, but slowly. There is no resistor on my board
at R186, which supposedly causes a slow spinner… but I'm not going to
go adding resistors if having no movement at all is not normal.

Other than all that, the board seems to be functioning properly.

So I assume the first thing I should do is replace the crystals with
the proper values, but in this document:
http://www.ionpool.net/arcade/mh/major_havoc_conversion.txt
it says "Also the integration capacitors are DIFFERENT depending on
the Y1 clock. If you change Y1 to a higher frequency, You will need
to change the integration capacitor to a larger value (???)." This
part is over my head, and it doesn't help that they don't give any
values to compare. I am hoping someone here can tell me what to look
for so I can revert this board to the proper components.

My biggest concern is the sound, There is no "P" displayed anywhere
that I noticed in the test mode screens, but I don't know if an only
partially bad Quad-Pokey would show up. I was wondering if anything
else could be affecting the sound chip (like the crystal speeds) or if
I need a Quad-Pokey eliminator board instead?

I guess I'll worry about the pincushioning and the spinner after I get
the clock speed and sound fixed, but if anyone has any thoughts on
those things too, I'd appreciate it.

Thank you for any assistance!
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Received on Fri Aug 19 18:55:47 2011