Re: Trying to restore modified Major Havoc board

  I think that the 2 channels of the pokey are mixed down to 2x2 via
op-amps... look on the last page of the schems..

http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Major_Havoc/Major_Havoc_SP-252_2nd_Printing.pdf

you might be lucky to just have a bad resistor or cap in one of channels
or a bad OP-Amp in 14R/S which only affects one channel. 14Q seems to
span both but you might just have a bad individual op-amp in that IC too.

On 8/19/2011 4:55 PM, Xyla wrote:
> 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 Sat Aug 20 19:22:56 2011