Re: Amplifone monitor - still stumped on bright dot in middle.

John Huie wrote:
> Just to refresh...this monitor on this Star Wars works good and the
> graphics are all there and everything but there's a constant bright
> dot in the middle. If I turn the brightness down enough for the dot
> to go away then I can't see the other graphics at all.
>
> Here's what I've tried so far:
>
> - Bought a whole slew of components from Bob Roberts to rebuild the
> deflection board and HV board
> - HV is good.
> - B+ is good.
> - Adjusting color drives doesn't help. Brightness down and the color
> drives up still won't let me turn down dot enough to see graphics well.
> - I don't have any spare parts to swap in. I only have 6100 vectors
> other than this.
> - double checked continuity from focus block wiring, all connections
> under boots are good. Good continuity back to HV board and color
> drives on deflection board are good.
> - Pins on neck not shorted to heater pins. (Except pin 4 which isn't
> used - could this be a problem?)
> - W jumpers are all long gone.
> - Resistors in neck board/ring are good.
> - Does same thing with known working PCB set.
> - Reflowed J103 and tested continuity along wires.
> - Ground to neck board/ring is good.
>
> Still not sure how to check Z signal. What components should I be
> looking at that are common to all 3 colors that could be causing this?
>
> Any other idea?
>
> Thanks everyone. I'm working on this for a friend of mine and just
> about at the end of my rope.
>
Z-Signal is the brightness. What sort of test equipment do you have? A
'scope would be best - you could check that the signal is varying. An AC
setting on your multimeter will give you an idea if there is change on
that signal, but I do not know what the result should be for your meter
or situation. If someone here has a voltmeter and can see what reading
they get on the Z-level when the board is on a set screen test that
would help you figure out if yours is working properly.

I suspect that signal is your problem though. Either it is not coming
from the board or it is not amplified by the monitor chassis or possibly
the picture tube has a cathode short and this negates the Z-axis level
completely. Not sure about that last hypothesis though...

John :-#)#

-- 
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Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
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"Old pinballers never die, they just flip out"
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