Re: G05-801 Tech

Jason,

Your complaint about retrace that can't be adjusted out indicates you have a
voltage wrong (somewhere). Since you didn't mention a focus problem, it's
most likely on G1 and/or the cathode. Both of these are derived from your
+90V supply, so that's a prime candidate. Regardless, check all of your
voltage supplies.

Your complaint about a spot after power down indicates the grid and cathode
are losing potential too quickly (relative to the crt cooling down). This
also supports the low +90V supply theory.

D509 and C506 are intended to suppress "the spot" after power down. If you
replaced C506 when you capped the monitor, you may have installed a
defective part, an incorrect part, or the part may have been installed
incorrectly. You didn't mention if the symptom was present before you capped
it, but that would be a good indicator.

If your +90V supply is good, check the voltage across C506. It should be
very close to whatever voltage you measured on the 90V rail. If it's not,
C506 or D509 may be defective.

One other note. The spot on the screen remains until the heater in the CRT
cools down, which is around a minute. The "voltage in the tube" can remain
for a much longer period of hours or even days or more. C506 is used to
ensure sufficient voltage to pinch off the beam, is present for at least as
long as it takes the heater to cool.

HTH. Let us know what you find.

Thanks,
-Mark
On Thu, Apr 30, 2009 at 9:50 PM, utahtaper <utahtaper@comcast.net> wrote:

> I'm debugging an 801. Monitor has been capped and bottlecaps replaced.
> The monitor fully works however there is always a dot right in the middle of
> the screen(Like a spot killer dot) not a bright dot, but a dot none the
> less. The dot is even still there when the brightness and contrast are
> turned all the way down. Never ran across this one before. Anyone seen this
> before and have some suggestions?
> The dot is also there when the game turns off and slowly disappears as the
> voltage in the tube drops. Or if I bleed it off myself with my probe.
> Thanks in advance!
> Jason
>

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Received on Fri May 1 02:30:25 2009