WG 7400 Random Shut Down

cointech

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Donor 3 years: 2018-2019, 2024
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I did a cap kit and checked for bad solder.
Monitor works fine most of the time but
will randomly just quit. sometimes in the middle of the day
and will sometimes work for days without failure.
When it stops if you power it off and back on it will come right back on.
Is there something that should be checked or replaced
do I need to adjust the B+ where should it be at?
Thanks
 
also have changed zener diode ZD701 and the caps C713 and C730 as
per the repair guide
 
with this line, when you have this problem you should go through with re-capping the entire chassis. put an alligator clip on TP202 (red meter probe) and another on your monitor frame (black meter probe) and set your meter on 200VDC after capping it.

you shouldn't have to mess with the B+ adjustment unless the pot's bad. at which point, you'd be better off removing and replacing it. I don't remember off-hand what resistance it's rated it though.. cause that epoxy they put on it is a bitch to remove and you'll probably wind up breaking the pot anyway lol
 
Where you at on this repair..

I did a cap kit and checked for bad solder.
Monitor works fine most of the time but
will randomly just quit. sometimes in the middle of the day
and will sometimes work for days without failure.
When it stops if you power it off and back on it will come right back on.
Is there something that should be checked or replaced
do I need to adjust the B+ where should it be at?
Thanks



The intermittent ones can be the worse to repair!

Good trouble shooting skill's maybe needed.

I have quick list of things you can do and see

what works..Along with the other KLOV members tips

Tapping on the chassis during
game play can let you know if the is a loose connection
Making sure your yoke plug is seated all the way down..

Confirm the female ac plug on your chassis pins are not
to spread out this can make you loose everything
and can be very intermittent..

That the large 7 watt cement resistor over in the
back left corner is solder in good..

And that you just sub out Q708 it can be very intermittent
and cause shut down..where the B+ jumps high and the
horizontal drive pulse is missing to the horizontal drive
stage. heating or cooling of the transistor may not be good
enough as a test to see if it is failing.

It takes Both the DC drive current from the SMPS
and the Horizontal drive current to the H.O.T to
Drive the fly and Yoke since they share the same Pulse..
on any standard or dual res monitor.
One without the other the monitor will shutoff.

If you need to know how to be sure your power supply
is in good working order then use the light bulb per the u2000
Sb any power supply you can use the bulb as a load test
to decide if the smps is working Good..

If you have tryed these let us know.
 
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