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
-

Kibo informs me that "Mark & Mary Ann Weiss"
stated that:

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.

I doubt it's your transistor, as your monitor wouldn't have come back
from the dead after failing the first time. More likely you have a dry
joint in a hot part of the PCB, or an overheating elecrolytic. It might
be hard to find the problem area, but at least it'll be a lot easier &
cheaper to fix than a failed flyback transistor.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

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
-

I doubt it's your transistor, as your monitor wouldn't have come back
from the dead after failing the first time. More likely you have a dry
joint in a hot part of the PCB, or an overheating elecrolytic. It might
be hard to find the problem area, but at least it'll be a lot easier &
cheaper to fix than a failed flyback transistor.



I had the chassis apart earlier this evening and went through the heat
sinks, tightening screws that hold the power devices to them. Some screws
were not snug, so I made them so. I also blew out some of the dust that had
accumulated on the flyback and HV wire. Reassembled cabinet and have been
running it for about 2 hours now. I'm waiting for it to reoccur.

It almost seemed like an arc problem, as the outage was usually accompanied
by an audible snap. I also made sure the HV wire didn't pass within 1/2" of
anything else by repositioning it a bit.

The odd part about this is that today is the first really cold day, our heat
has not been turned on yet, so it's chilly in the office, and the monitor
fails. Not last week when it was 77º in here.

I suspected a semiconductor because I have seen some types of semiconductors
go 'soft' and become temperature sensitive. I didn't have a can of
refrigerant spray handy, so I could not test my hunch with this one however.
The capacitors are also a candidate, as is the potential of solder problems.
Frankly, I hope I don't have to disassemble it that far. The solder side of
the PCB is, as you probably can imagine, only accessed once you've
COMPLETELY disassembled the chassis. That could take more than an hour. I
think it was 28 screws just to get the back cover and cage removed. I'll say
a prayer that it was either a loose screw or a dust problem causing arc and
current limit foldback.

Thanks for the suggestions.


--
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
-

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

Yeah, come to think of it, I've never seen a power device come back from the
dead. Usually it's logic devices and other semis based on low power
technology.


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.

I am really hoping it's not IN the flyback transformer. That would be darned
difficult to replace. I remember buying an HP 1740A o'scope back in '82 and
having it fail one day past the warranty. I had to get a buddy of mine who
worked for Penril Corp to order a new one for me, as HP wouldn't sell me the
flyback transformer directly. It cost me about $140 back then, but
considering I'd paid $3800 for the 'scope, it was a good deal.
Electrolytic caps... oof.. just try and get to the solder side of the PCB on
this thing! I'd have to disassemble to almost complete to get to that area.
As for dry joints, sometimes they have a mechanical correllary. I once was
given a Nanao monitor that had no vertical scan. When turned on, it would
display a horizontal line. A good sharp rap on the side of the chassis
brought the vertical back. I vaguely recall that out of dozens of joints I
reflowed, it was one near a transformer that turned out to be the baddie.

I had a chance to observe the problem again, as it's back today. When it
goes out, I hear the bleeder doing its thing. It sounds just like when the
monitor goes into power save mode. The snapping sound was an exaggeration of
my memory of what happened. Turn the power off, turn the power on, hear the
degauss coil fire, raster comes back, raster 'zooms', loses focus, and fades
to black at teh same time, followed by the sound of the bleeder (very slight
snapping sound common to monitor being shut off). If I turn it back on, it
repeats. If I wait, I can turn it on and use it a while before it recurs.



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.

I gotta get a HV probe. I'm in RF electronics and usually rely on front
panel meters to read the 10kV plate supply on the transmitter, so have never
needed a probe. One problem: without a schematic, it's going to be rather
difficult to make some of these measurements. Is there a standard color code
for the wires coming out of the flyback? This one has two grid voltage
adjustments and one focus adjustment. If memory serves me, there are three
wires coming off the top, one of which is the HV to the anode.



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.

Yea, damn them. I tried to order a schematic from them years ago after one
of the FG series developed a vertical jitter problem during warmup. They
were hard-nosed about not allowing me to obtain repair information.
I would be very concerned about the quality of an after-market FB and
whether it would even fit without substantial modification to the PCB. Image
quality is very critical as this is being used in a CAD/3D modeling system.
I just can't see wasting this monitor, as it is barely used. I have the
power save function set to 5 minutes of non use, so the monitor actually has
very few hours on it because it lived 95% of its live on standby. It was
bought, I recall, in summer 2001, making it one of the newest pieces of
hardware in this office. With the sluggish local economy, many other big
drains on my budget, and a cash shortage, I'm not in the market to just go
out and buy another CRT.

Whatever happened to Sam's PhotoFacts? I used to be able to get schematics
of anything back in the '50s and '60s through them.


--
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
-

I've got the unit completely apart. It was a pain in the butt, with all the
hot melt glue NEC used around the neck of the tube and socket assy.
Disconnected all the wiring to the motherboard, removed the board. I have
about 50-60 screws all layed out on the bench that I removed to get this
far!
I desoldered the flyback and removed it. I'm reflowing solder on every
component in that quadrant of the board and in areas where other components
are able to stress the joint, or where the joint looks dull.
Going to clean the FB trans in acetone and then reassemble and see what
happens.
If I had a Huntron Tracker, I'd be better able to troubleshoot without a
schematic. Unfortunately, I no longer work for the company that had them.

Wish me luck!


--
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
-

Got the monitor reassembled last night.
Fired it up from a cold start, and the problem manifested itself right then.
Cycled the power off then on twice, before the raster image would stay on.
Monitor worked for a couple of hours. I went to bed.
Next day, turned the monitor on, got a few minutes' use and there was an
audible 'snap' sound and the zoom/defocus/fade to black event recurred.
Powered off and on, but problem would just repeat.
Wait 20 minutes, and powered it back on. It stayed on for as long as I was
using it.

The problem is very much intermittent and does not seem to be related to
temperature as I had first thought.

I did throroughly clean everything remotely related to high voltage. In
fact, the monitor was clean to begin with, but now it's as clean as when it
came off the assembly line. I just wish I had a schematic so I could better
pinpoint the problem. I'll bet it's one component that's causing this. Would
be a shame to scrap such a great tube just because of a possible capacitor
or flyback problem.

A friend suggested I get an LCD, but I can't find one in the 21" range with
a native 2048x1536 resolution, much less one in the $500 price range.
Working with a monitor that you don't know how long before it decides to
shut off is really frustrating.


--
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
-

Kibo informs me that "Mark & Mary Ann Weiss"
stated that:

Got the monitor reassembled last night.
Fired it up from a cold start, and the problem manifested itself right then.
Cycled the power off then on twice, before the raster image would stay on.
Monitor worked for a couple of hours. I went to bed.
Next day, turned the monitor on, got a few minutes' use and there was an
audible 'snap' sound and the zoom/defocus/fade to black event recurred.
Powered off and on, but problem would just repeat.
Wait 20 minutes, and powered it back on. It stayed on for as long as I was
using it.

Betcha the 'snap' is the protection circuit kicking in.

The problem is very much intermittent and does not seem to be related to
temperature as I had first thought.

I did throroughly clean everything remotely related to high voltage. In
fact, the monitor was clean to begin with, but now it's as clean as when it
came off the assembly line. I just wish I had a schematic so I could better
pinpoint the problem. I'll bet it's one component that's causing this. Would
be a shame to scrap such a great tube just because of a possible capacitor
or flyback problem.

Like I said before; the first thing I'd do is get out the soldering iron
& the solder-sucker, then go on a dry-joint hunt.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

I did throroughly clean everything remotely related to high voltage. In
fact, the monitor was clean to begin with, but now it's as clean as when
it
came off the assembly line. I just wish I had a schematic so I could
better
pinpoint the problem. I'll bet it's one component that's causing this.
Would
be a shame to scrap such a great tube just because of a possible
capacitor
or flyback problem.

Like I said before; the first thing I'd do is get out the soldering iron
& the solder-sucker, then go on a dry-joint hunt.


That's why I took the entire motherboard out in the first place. I spent 2
hours desoldering and reflowing solder all over that board!

Hard to imagine a capacitor having dried out, but I can't rule out a
defective batch (as what happened with Gigabyte motherboards a few years
back) either. I just don't have any documentation by which to trace out the
suspect components. Shipping it to a repair facility plus the repair cost
will cost as much as a new monitor, and I may not get as perfect a tube. I
hope my other NEC AS120 isn't going to follow this one. I rely on them both
very heavily.
Oddly, my wife criticized me for setting my Windows standby timer to 5
minutes. Perhaps having it shutdown so often has stressed the components
with extra startups. But at $240/month, I can't afford to let the monitors
run when I'm away from my desk. Ggggrrrr...


--
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
-

The monitor has been working in an intermittent basis. I was using it this
evening and it shut down without warning. Power off/on and the usual symptom
appears, with the zoom, blur and fade out routine.
Turned it off/on about 50 times in as rapid a succession as the delay timer
would allow, and suddenly, it stayed on. So I went back to work on my
project.
Somehow, I have to wonder if it's a flyback when I can cycle the power
numerous times and get the unit to function normally again.


--
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
-

Can e-mail you service info and schematics, IF yours is an LG CN291E
chassis. What is your e-mail addy?

Wayne

On Wed, 06 Oct 2004 05:46:54 GMT, "Mark & Mary Ann Weiss"
wrote:

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
-

"Wayne" wrote in message news:417124f3.2395624@shawnews...
Can e-mail you service info and schematics, IF yours is an LG CN291E
chassis. What is your e-mail addy?

Wayne


Just remove the X from my addy and you've got it.

I tried to e-mail you privately but the domain was invalid.

Here's the gist of what I wrote:

Hello Wayne,

I don't have the cover off this monitor at the moment. Where is this number
typically located on this model?

I note that there is a sticker showing March 2001 as mfg date. Place of mfg
is Korea.

Thanks!


I'll add that I can consistently restart this monitor by toggling power 30,
40, as must as 60 times, and it will stay on. I disabled my screen standby
feature in Windows XP and let the monitor run all night. It's still on and
operational 24 hours later. So it appears the problem is related to being
put on standby.


--
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
-