Re: G08 width and centering problem

More testing-
  Swapped the two yoke wires on the X side and the centering issue switched sides. I guess this means the yoke is OK and the electronics are faulty.
  I also swapped the X and Y paddle boards. Problem remained with X side. My voltmeter doesn't have enough resolution to measure those .13 ohm resistors anyway- .1ohm resolution.
  The yoke DC resistance measures about the same as another G08 I have anyway.

  One thing I noticed when trying to measure bias along the amp path- R725 (and R625) have 180 ohm resistors versus 240 ohm resistors in place. In schematics with the paddle boards, these show up as 240. Older schematics (actual G08 manual) show 180 ohms.

  Since I have replacements, I will probably go ahead and replace Q701 and Q702 to see if that corrects it.
  The last time that I narrowed something down to the deflection section on a G08 and couldn't make sense of it, shotgunning the transistors there fixed it. Will let you all know.

  Kerry

---- William Boucher <wboucher6@cogeco.ca> wrote:
> The more I read the thread on this problem, the more I think that you have a
> faulty yoke coil. If several turns on the X coil are shorted on the side
> that pulls the beam left, then the ampere-turns product will be lower on
> that side (weaker field) and it won't be able to pull the beam to that side
> as far as it should. It sounds like you have exhausted all possible
> electronic possibilities. If you can swap the polarity of the X coil, you
> can see if the problem remains on the same side. The picture will mirror,
> but if it is still short on the left and long on the right, electronics is
> not the problem. Measure the resistance of the coil to see if it is the
> correct value. The X axis coil resistance should be a bit lower than the Y
> axis coil. Since your Y axis is okay, that tells me that there's no problem
> with the power supply levels. Swapping the paddle boards, as was previously
> mentioned, is also a good idea to see if the horizontal one is limiting on
> one side.
>
> Good luck with it,
>
>
> William Boucher
> http://www.biltronix.com
>
>
> ----- Original Message -----
> From: <kstillinger@sc.rr.com>
> To: <vectorlist@vectorlist.org>
> Sent: Friday, April 29, 2011 4:38 PM
> Subject: VECTOR: G08 width and centering problem
>
>
> > Hey-
> >
> > I've been looking at a G08 here for a few weeks now on and off.
> > Everything else finally fine, the width is not sufficient to fill the
> > screen and the centering is off.
> > I've tried a bunch of different stuff and replaced parts for other issues
> > along the way.
> > The 'left' side of the image won't reach all the way over. Messing with
> > the horizontal width and centering pots can only get it about halfway from
> > center to the side. The problem persists with different input protection
> > boards and output transistor assemblies. I replaced Q704 MPSU60 with a
> > recommended equivalent (MPSW92) and first thought the problem was due to a
> > mismatch with the old Q703 (MPSU10) so I subbed the recommended MPSW42.
> > No change.
> > Both X and Y signals look nicely centered around 0V, so that's not where
> > the offset is coming from. Twisting the Horz centering pot to each side
> > seems to affect the right side more than the left. I can actually get the
> > right side shifted off to where it is clipped. Even the Hwidth pot seems
> > to affect the right much more than the left.
> >
> > I thought the horizontal side R735 3 ohm 20W measured too low around .8
> > ohms and I thought- that could do it. Shoot no.
> >
> > I figure I might try to swap the X and Y paddle boards and see if the
> > problem follows the board.
> > This is really bugging me. I can't see where the problem is being
> > introduced.
> >
> > Any ideas are appreciated.
> > Kerry
> > ---------------------------------------------------------------------------
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> > http://www.vectorlist.org
> > ** Please direct other questions, comments, or problems to
> > chris@westnet.com
>

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Received on Mon May 2 12:27:56 2011