With a horizontal output transistor, it will usually be good or bad. I
have never seen one go out and come back to life!

Without properly investigating the fault it would be difficult to guess
at what may be going wrong. In TV sets and monitors, the areas that can
cause your description (you described it well), can be from the high
voltage multiplier, main power supply, and from a cold solder connection
in these areas. Many times, I have seen electrolytic capacitors going
bad in various areas to cause such problems. The most common cause of
the fault that you are describing is the high voltage multiplier. I
believe that on your monitor it is part of the flyback assembly.

Measuring the outputs of the main power supply, the G2 bias voltage for
the CRT, the focus voltage, and also the high voltage for the CRT, would
be a good start. For the measurement of the focus voltage, and the high
voltage, you will need a high voltage probe for your meter.

As for original parts and service, I doubt that NEC will sell any parts
or schematics to outside servicers. There are some after-market flyback
transformers available for many types of monitors. I have heard
conflicting reports about how good or bad they are.

--

Jerry G.
======

"Mark & Mary Ann Weiss" wrote in message
ink.net...
Just tonight, one of my two NEC AccuSync 120 monitors blinked, made a
discharge noise, and then caused the raster to magnify, defocus and fade
to
black. Switching the monitor off and back on resulted in a repeat of
this
behavior. Switching the monitor off for a minute then switching it back
on
resulted in normal operation for about 2 minutes.

I removed the cover and the metal cage surrounding the electronics and
have
been running the monitor for close to an hour now, but have not been
able to
repeat the failure, presumably because of the lower operating
temperature.

I suspect it's a horizontal output transistor, since most systems make
that
a critical part of the HV flyback loop and they are the most stressed
component.

Side comment: I also own a NEC 6FG, circa 1992, and have peeked inside
that
chassis years ago. The difference between the construction of that
monitor
and this one is startling. The heat sinks have shrunk tremendously!
(BTW,
the 6FG still runs perfectly after 14 years 24/7 operation.)

My question is where I can get a schematic and parts list for the
AccuSync
120, and if these transistors are available through the usual channels
(Digikey, Mouser, etc).


--
Take care,

Mark & Mary Ann Weiss

VIDEO PRODUCTION . FILM SCANNING . DVD MASTERING . AUDIO RESTORATION
Hear my Kurzweil Creations at: http://www.dv-clips.com/theater.htm
Business sites at:
www.dv-clips.com
www.mwcomms.com
www.adventuresinanimemusic.com
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