Re: VECTOR:TECH Space Duel Monitor

On Mon, 14 Aug 2000, Matt J. McCullar wrote:
> Steven Zeuner wrote:
> >
> > On power up, there is no spot killer. HV is present, with just an eerie
> > glow on screen. You can see that the game is playing as the image moves.
> > It's mostly a 1 inch circle.
> >
> > Any ideas what could be smoking R100? I did check continuity on all the
> > power transistors and there fine.
>
> Most likely there is something shorting out the +28-volt line. It pulls
> too much current through Q100, causing R100 to fry. Q100 may be
> shorted. With the 28-volt line failing, that will also cause the high
> voltage circuitry to not perform properly.
>
> Check all diodes and transisors on the deflection board. The MPSU07 and
> MPSU57 transistors love to short out. Also make sure the 28-volt zener
> diode at ZD100 isn't shorted, or the 1N914 at D104.

I concur with Matt that there's a +28V problem on this board.

On an unrelated note, I had a G05 that powered up and gave me an
eerie glow on the *top* of the screen, as if the monitor were trying
to fire the beam through the top of the monitor several inches before
the beam hit the screen. The spot killer was on.

The relevant deflection transistor on the monitor chassis got extremely
hot, as did R620 (the big ceramic one between the MPSU07 and MPSU57
heatsinked transistors).

Turned out that the deflection transistor was fine, as were the U07 and
U57 transistors. The problem was a dead-shorted Q605 - a little 2N3906
general-purpose transistor. Replacing the $0.07 part fixed the board.

ObHack:

NTE49 and NTE50 are replacements for MPSU07 and MPSU57, but I'm not sure
which replaces which. But if you're in a pinch and can't find exact
replacements, you can figure out which is NPN and PNP and make the
substitution.

Later,
Doug.

-- 
 dougj   |
   @     |
hwcn.org |
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