Re: Major Havoc pincushion question

I just recently purchased a working SD-to-MH converter board from someone on
KLOV. It is shipping to me now and it will be arriving with the full
schematic for the board. Also provided will be the schematic for the
encoder and other stuff and also the full conversion instructions, all
specific to Space Duel, not Tempest. I can scan these docs and email them
to you or post them on my site once I get my mits on them sometime a couple
of weeks from now.

I'm no expert regarding this topic so feel free to laugh at my ignorance
after I ask this... but is it possible that your monitor has the wrong yoke
for the application? If the yoke on SW corrects for pincushion and if the
converter board also does, then it would possibly be doing it twice by
applying both methods? The pictures that I've seen posted look like you
need a "reverse pincushion" or "de-correction" board, that's commonly known
as "barrel" correction. Most monitors will use just one pot to adjust the
geometry to create either the pincushion or barrel effects and you adjust
the pot until things are straight. If a correction board can be adjusted
through unity gain, assuming that unity gain does nothing, then it should be
able to either reduce pincushion or add barreling, whichever is required
depending on the overall system to produce straight line output.

Since Clay's board has a pot, I'm betting that it'll correct the problem
regardless of whether it needs to reduce or increase the gain of X through
the 1495 as Y changes (or something like that anyway). I'm sure that it'll
depend on the overall values of the gain setting resistors used on the
board.

William Boucher

----- Original Message -----
From: "Total Impulse" <totalimpulse@comcast.net>
To: <vectorlist@vectorlist.org>
Sent: Monday, October 26, 2009 6:45 PM
Subject: Re: VECTOR: Major Havoc pincushion question

>
> It definitely reminds me of my Star Wars (has a 6100) before I installed
> your correction board.
>
> I've now checked all the resistors and they seem fine. I also went
> through and checked for broken traces. For fun, I went ahead and replaced
> the two electrolytic caps and all eight little 0.1 caps as well as the
> 7815 and 7915. I also carefully desoldered the 1495's, installed sockets,
> and a new pair of 1495's. After all that, the amount of pincushioning is
> still the same. I have +6.8 and -15 volts at the 1495's, but forgot to
> check the +15.
>
> Does anyone have a copy of the schematic for the Major Havoc to Space Duel
> adapter board? All I can find is the one for Tempest, and all the
> component labels are different.
>
> Anybody out there have a Major Havoc conversion who can tell me if they
> have more or less pincushioning than I do?
>
> Thanks,
>
> Alan
>
> Clay Cowgill wrote:
>>> Is this amount of pincushioning normal for this situation?
>>> (Major Havoc conversion pcb with Space Duel adapter pcb and WG K6100)
>>
>> Doesn't look right to me-- that might even look worse than no correction
>> at
>> all! ;-) I would be suspicious of the correction board operation. Check
>> for any
>> cracked resistors around the 1495's (from rough handling or something).
>> There's a couple resistors that essentially set the correction 'level'
>> and a
>> problem there could lead to 'no correction' on the output signal. (I
>> used a
>> potentiometer on my display corrector for that part of the transform, but
>> the original boards have a pair of fixed resistors.)
> --
> Total Impulse - Just Having Fun!
> Alan Estenson, totalimpulse@comcast.net
>
> ---------------------------------------------------------------------------
> ** Unsubscribe, subscribe, or view the archives at
> http://www.vectorlist.org
> ** Please direct other questions, comments, or problems to
> chris@westnet.com

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Mon Oct 26 19:53:32 2009