Re: Major Havoc pincushion question

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 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, 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.

(and I likely didn't need to have done any of that work to the adapter
board.)

Thanks everyone!

Alan

-- 
Total Impulse - Just Having Fun!
Alan Estenson, totalimpulse@comcast.net
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