Major Havoc pincushion question

mnrocketry

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I'm nearing the end (hopefully) of a Major Havoc conversion in a Space
Duel cabinet. I have it up and running, but it seems like there's a lot
of pincushion.

Large pics:
http://www.mn-rocketry.net/misc/arcade/photos/major_havoc_pincushion-1.JPG
http://www.mn-rocketry.net/misc/arcade/photos/major_havoc_pincushion-2.JPG
(smaller pics are attached to this post)

Is this amount of pincushioning normal for this situation?
(Major Havoc conversion pcb with Space Duel adapter pcb and WG K6100)

I understand that the adapter pcb is supposed to be doing some
pincushion correction. Could something be not working properly there?

Thanks,

Alan
 

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Well, I've just been told by an expert that it's definitely not right! Time to start checking out the adapter board for problems.
 
For starters, fix the Y linearity...

I don't thing the converter board will ever make it truly pincushion free... it just gives you another set of knobs to turn that are more likely to muck things up =-P
 
I believe that I had read that original Major Havoc was designed to run on Atari Amplifone monitors and hence when using a Wells Gardner, that some of this was supposed to be normal. I have a Space Duel conversion and I don't think I ever got the sides flat either (although I don't remember it as big a gap as yours has). I will pull out my machine out of storage soon and run it and see what I have....
 
For starters, fix the Y linearity...
I don't thing the converter board will ever make it truly pincushion free... it just gives you another set of knobs to turn that are more likely to muck things up =-P

After I took those pics, I went through and adjusted the linearity, bip, size, etc... I just didn't take new pics afterwords.

My question essentially boiled down to - is this amount of pincushioning normal for this situation? (Hoping that someone out there with a Major Havoc conversion would look at theirs and tell me "yes" or "no".)

I once worked on a Tempest board set that showed pincushioning like this. I eventually found a broken trace in the circuitry around the 1495's. Fixed that, and the pincushioning disappeared.

Alan
 
I know you saw this already, but in case it may help someone who searches out this thread later...

This is in a Space Duel with NO conversion board. i.e no pincushion correction in place.

CIMG1683.JPG
 
Fixed it. There was nothing wrong with the adapter board; Atari screwed up the Major Havoc board right from the get-go. Long explanation below:

Moral of the story - Don't assume that Atari was infallible
(or, Garbage In, Garbage Out)

While I was supposed to be writing a report this morning at work, I sat looking at the schematic for the Major Havoc to Tempest adapter board (not having one for the Space Duel version), followed by sheet 8B of the Major Havoc schematic, followed by the MH pinout, followed by an Atari service bulletin on Major Havoc.

To summarize, factory jumpers are added to the Major Havoc board to bring a "pre X" signal to pin N and a "pre Y" signal to pin M on P18 (cutting those two pins from the ground pad). The normal "X out" (P18 pin 9) doesn't connect to anything on the adapter board. The normal "Y out" (P18 pin L) connects straight through the adapter board. The adapter board does its pincushion correction and generates "X out" given the two "pre" signals.

First, I decided to assume that the adapter board was fine. I then realized that if the adapter board was getting pre-X and Y-out but no pre-Y, I'd probably get a picture, but without any pincushion correction. Once home from work, I took a look. The pre-X was correctly jumpered to pin N. However, the pre-Y was jumpered to P20, pin D! That pin connects to absolutely nothing on the adapter board. This appears original; pin M had never been cut from the ground pad. So, pre-Y on the adapter board was actually connected to ground.

So, I cut the errant jumper off, cut the trace to the ground pad at pin M, ran a new jumper to it... Presto! I have pincushion correction and a much spiffier picture.
 
Good job. I remember now seeing the cut traces on the PCBs I have. If you can kindly take similar after pics for us for the record, that would be great.

And again, I believe this was done with the introduction of WG monitors (the Space Duel and Tempest conversions) which had problems with the pincushion compared to Atari Amplifone in the first place.
 
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And again, I believe this was done with the introduction of WG monitors (the Space Duel and Tempest conversions) which had problems with the pincushion compared to Atari Amplifone in the first place.

Yep. Major Havoc (and Star Wars) were designed to use Amplifones. The Amplifone yoke design took care of the pincushioning, so there wasn't any pincushion correction circuitry on the game board (as there was on Tempest, Space Duel, etc...). When you connect either MH or SW to a K6100, you get pincushioning. When Atari released Major Havoc as a conversion kit, they came up with the adapter boards. They did two things - adapted for the different pinout in the wiring harness and added a pincushion correction circuit.
 
Yep. Major Havoc (and Star Wars) were designed to use Amplifones. The Amplifone yoke design took care of the pincushioning, so there wasn't any pincushion correction circuitry on the game board (as there was on Tempest, Space Duel, etc...). When you connect either MH or SW to a K6100, you get pincushioning. When Atari released Major Havoc as a conversion kit, they came up with the adapter boards. They did two things - adapted for the different pinout in the wiring harness and added a pincushion correction circuit.

So if one has a Star Wars with WG K6100, there is pincushioning that cannot be corrected then I guess.
 
So if one has a Star Wars with WG K6100, there is pincushioning that cannot be corrected then I guess.

Well, I have a Star Wars with a K6100. What I did was to install the "Wells Gardner Color Vector Monitor Display Corrector" from
http://www.multigame.com/display.html

They're out of production, but Clay has talked about doing one more run of them. Email him and you may be able to get on the list.

Alan
 
I'm having similar problems with my WG 6100 too-- Sent an email from his site!
 
If you can kindly take similar after pics for us for the record, that would be great.

Here are two pics showing what my Major Havoc looks like when the pincushion correction on the adapter board is working properly. Quite a difference! Compare to the pics attached to my first post in this thread.

Alan
 

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Thanks for posting the after pics Alan. It will come in handy when I pull out my MH Space Duel conversion and check for the same thing.
 
The strange thing is that I have a pincushion (bad) like you showed before on my SW cockpit, but I _do_ have a 25" Amplifone in there.....

WEIRD !

That's why I want that PCB from Clay !

The difference is quite amazing and convincing !!!
 
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