Greetings, distinguished repair specialists,

I have been using a 21" Hitachi CM813ET CRT monitor for some time now. It
exhibits the strangest phenomenon every now and then. Prompting me to write
this message is the fact that it today appears stronger than ever. I have
gone through the excellent monitor repair faq at
http://repairfaq.ece.drexel.edu/sam/monfaq.htm, but I'm still a bit
uncertain of where I should start looking. I'll describe the problem in
detail and hopefully you guys can give me some pointers.

First of all, the phenomenon either happens or it does not happen. If it
does not happen, everything is perfectly normal. The picture is crisp and
centered, nothing is out of the ordinary. When it does happen, however, the
picture shifts about 1 cm to the left and becomes jittery. Mainly,
consecutive horizontal lines are not aligned perfectly, but individual lines
can shift left or right on each redraw, making the screen look like it
shimmers very nervously.

The amount of jitter varies greatly. At times, the jitter is barely
noticeable, with movement range of only 1 pixel or so. Sometimes it can
extend to several centimeters and occasionally the monitor completely loses
horizontal sync, drawing nothing but messed up lines on the screen,
accompanied by a high-pitched whine. The whine is not there during lesser
jitter or normal operation.

As I said, the condition looks like someone is using a pot with an integral
switch to control it. It's easy to detect when the condition is "on" because
the image is shifted left. Then the amount of jitter ranges back and forth,
never jumping quickly from total chaos to relative order or back, but
gradually shifting between these states.

Thus far the condition has been fixed by simply turning off the monitor for
a second or thirty and then turning it back on. It might exhibit some jitter
for a couple of seconds after being turned on, but would then settle down
and work properly. Please note that I'm not confusing this with the normal
startup-degauss-wobbling of the screen. This time, restarting the monitor
doesn't seem to help and as I'm writing this, the monitor is turned off,
disconnected and resting so that I can see if extended cooling time does
anything for it.

I should mention that I have ruled out all external noise sources as the
cause of this by operating the monitor in different rooms and with different
computers, without having a cellphone with me or anything such. Bad scan
rates are also out of the question because once this condition exhibits
itself, the same jitter is visible even in the monitor's own "power saving"
logo that displays for a couple of seconds after disconnecting all input
signal, or after turning the monitor on without input signal.

None of the monitor's adjustments have any effect on the phenomenon, nor
does alternating between the two inputs or degaussing the monitor. Whacking
or physically abusing the monitor has no effect either. Nothing
distinguishable from the normal drifting anyway.

My understanding, based on the monitor repair faq, is that there is clearly
something wrong with the horizontal deflection circuitry. Since percussive
maintenance has no effect, I would almost be willing to rule out a cold
joint as the primary reason, focusing more on a possibly faulty component
somewhere either in the power supply of the horizontal deflection or in the
late parts of the signal path.

Without leading you guys any further astray with my possibly mistaken
conclusions, I would like to tap to your collective intellect in order to
gain insight as to what precisely look for when I finally open the beast up.
If any of you have experience with similar problems, or can supply the
schematics of this (or similar) Hitachi monitor, please don't refrain from
replying. Your help is deeply appreciated.

--

Arto Rantala

Arto Rantala wrote:
When it does
happen, however, the picture shifts about 1 cm to the left and
becomes jittery. Mainly, consecutive horizontal lines are not aligned
perfectly, but individual lines can shift left or right on each
redraw, making the screen look like it shimmers very nervously.

Having turned the monitor back on and with the jitter continuing, I should
restate this part. The jitter is not quite so high frequency as to put each
line at a random position wrt other lines. Looking at the right side of the
screen, the wavelength of the wave inherent in the supposedly straight right
side edge is about 1-2 cm on average, putting around 20-30 waves per redraw,
putting the wobbling frequency around 2 kHz. I don't know if this is
relevant in any way, but I didn't want anyone to make conclusions based on
bad information.

--

Arto Rantala

"Arto Rantala" bravely wrote to "All" (18 Mar 05 15:03:08)
--- on the heady topic of "Hitachi CM813ET image jitter"

It may be arcing internally. If you turn up the brightness to max and
it lessens or stops the symptom then that is it. If no change then it
may be a number of other causes.

Perhaps the arcing can be confirmed as it typically gives off acrid
smelling ozone gas and can be seen as corona or sparking effects in
the dark. Arcing can often be provoked by high humidity. Arcing also
tends to radiate interference to radio and TV.

You discussed vibration as not affecting the problem but many devices
may have heat sensitive internal joints which are not very sensitive
to vibration by comparision to cold solder joints. Among these are
electrolytic caps, resistors, transistors, IC's, etc.

What is your repair experience? Remember there are lethal voltages
inside monitors.

A*s*i*m*o*v


AR From: "Arto Rantala"
AR Xref: aeinews sci.electronics.repair:43351

AR Greetings, distinguished repair specialists,

AR I have been using a 21" Hitachi CM813ET CRT monitor for some time now.
AR It exhibits the strangest phenomenon every now and then. Prompting me
AR to write this message is the fact that it today appears stronger than
AR ever. I have gone through the excellent monitor repair faq at
AR http://repairfaq.ece.drexel.edu/sam/monfaq.htm, but I'm still a bit
AR uncertain of where I should start looking. I'll describe the problem
AR in detail and hopefully you guys can give me some pointers.

AR First of all, the phenomenon either happens or it does not happen. If
AR it does not happen, everything is perfectly normal. The picture is
AR crisp and centered, nothing is out of the ordinary. When it does
AR happen, however, the picture shifts about 1 cm to the left and becomes
AR jittery. Mainly, consecutive horizontal lines are not aligned
AR perfectly, but individual lines can shift left or right on each
AR redraw, making the screen look like it shimmers very nervously.

AR The amount of jitter varies greatly. At times, the jitter is barely
AR noticeable, with movement range of only 1 pixel or so. Sometimes it
AR can extend to several centimeters and occasionally the monitor
AR completely loses horizontal sync, drawing nothing but messed up lines
AR on the screen, accompanied by a high-pitched whine. The whine is not
AR there during lesser jitter or normal operation.

AR As I said, the condition looks like someone is using a pot with an
AR integral switch to control it. It's easy to detect when the condition
AR is "on" because the image is shifted left. Then the amount of jitter
AR ranges back and forth, never jumping quickly from total chaos to
AR relative order or back, but gradually shifting between these states.

AR Thus far the condition has been fixed by simply turning off the
AR monitor for a second or thirty and then turning it back on. It might
AR exhibit some jitter for a couple of seconds after being turned on, but
AR would then settle down and work properly. Please note that I'm not
AR confusing this with the normal startup-degauss-wobbling of the screen.
AR This time, restarting the monitor doesn't seem to help and as I'm
AR writing this, the monitor is turned off, disconnected and resting so
AR that I can see if extended cooling time does anything for it.

AR I should mention that I have ruled out all external noise sources as
AR the cause of this by operating the monitor in different rooms and with
AR different computers, without having a cellphone with me or anything
AR such. Bad scan rates are also out of the question because once this
AR condition exhibits itself, the same jitter is visible even in the
AR monitor's own "power saving" logo that displays for a couple of
AR seconds after disconnecting all input signal, or after turning the
AR monitor on without input signal.
AR None of the monitor's adjustments have any effect on the phenomenon,
AR nor does alternating between the two inputs or degaussing the monitor.
AR Whacking or physically abusing the monitor has no effect either.
AR Nothing distinguishable from the normal drifting anyway.

AR My understanding, based on the monitor repair faq, is that there is
AR clearly something wrong with the horizontal deflection circuitry.
AR Since percussive maintenance has no effect, I would almost be willing
AR to rule out a cold joint as the primary reason, focusing more on a
AR possibly faulty component somewhere either in the power supply of the
AR horizontal deflection or in the late parts of the signal path.

AR Without leading you guys any further astray with my possibly mistaken
AR conclusions, I would like to tap to your collective intellect in order
AR to gain insight as to what precisely look for when I finally open the
AR beast up. If any of you have experience with similar problems, or can
AR supply the schematics of this (or similar) Hitachi monitor, please
AR don't refrain from replying. Your help is deeply appreciated.

.... :) What does that wire do? =8Q (oh!)

Just to make a comment, this is one big long description! And, it is
well written. Have you thought of taking up literature, at the
professional level?

--

This is not the type of fault that can be analysed over an email. The
fault would only be able to be found by verifying voltages, and
observing for the proper waveforms or looking for noise in the supplies
to the various circuits.

From the way you are describing the fault, this can be from noise due
to open bypass capacitors, or there may be some arching in a component
somewhere.

There is no way to accuratly tell you an exact fix. This is where a
properly trained skilled technician, who has the proper diagnostics
equipment, would have to work on the monitor.

One big problem with the computer monitors, is that the manufactures
will not sell service parts, or schematic diagrams to non-authorised
factory service techs.

If you call Hitachi, and ask about who is servicing their computer
monitors, I am sure that they will recomend where to bring it.

If the monitor is about or more than 5 years of age, I would strongly
recomend that you start shopping for a new one. I would not put a lot
of money in to an old CRT monitor. These can be now purchased at a very
low price in relation to the cost of servicing them.

Jerry G.
======

Thank you for your replies, Asimov and Jerry,

Asimov wrote:
It may be arcing internally. If you turn up the brightness to max and
it lessens or stops the symptom then that is it. If no change then it
may be a number of other causes.
This is definitely something I have to check. Brightness is pretty much the
only adjustment I haven't tried so far. Right now the monitor isn't
exhibiting the symptoms, but I shall check this out when the problem
inevitably returns.

Perhaps the arcing can be confirmed as it typically gives off acrid
smelling ozone gas and can be seen as corona or sparking effects in
the dark. Arcing can often be provoked by high humidity. Arcing also
tends to radiate interference to radio and TV.
I must say that I haven't smelled anything out of the ordinary. Nothing in
the very familiar ozone smell range anyway. I haven't noticed any problems
with RF reception either, nor do I remember hearing any crackling from the
monitor. I'll have to recheck all that though just to be sure.

You discussed vibration as not affecting the problem but many devices
may have heat sensitive internal joints which are not very sensitive
to vibration by comparision to cold solder joints. Among these are
electrolytic caps, resistors, transistors, IC's, etc.
True. My intention is to at some point open the case and use cold spray to
find any such heat sensitive components. There are, however, a lot of
components in a monitor, making it rather difficult to just start spraying
around, which is why I would have been interested in learning of any
starting spots anyone could suggest.

What is your repair experience? Remember there are lethal voltages
inside monitors.
I have fixed amplifiers and such in the past and done some focus tuning to
older monitors, and for those have spent considerable time learning about
the hazards of CRT monitors. I know where the dangerous parts are and would
rather read 10 books to find out about a component rather than poking it
with my finger to see what happens. This echoing the reasons for writing
here before even opening the case up so that I would have some idea of what
to look for.


Jerry G, thank you for your compliment. I like to write clear descriptions
because it not only helps others understand the problem precisely, it also
helps me outline the problem for myself.
I bought the monitor a couple of months ago used for about 100 EUR.
According to the backplate it's built in '99. Its history is such that the
person I bought it from had gotten it from his workplace where it had shown
the symptoms. He took it home and never had any problems with it. After I
brought it home, the problems were there, but were so rare that I figured it
was still worth the price I paid for it (this monitor has _excellent_ image
quality!) so we agreed that I'd be keeping it regardless of the problems. I
might still be able to take it back, but I'm not sure if I want to.
Nevertheless, considering this person never had any problems, it would seem
that humidity or some other environmental aspect could indeed play a major
role here.
I could take it to be repaired, but as you said, it would probably cost way
too much. Being the student that I am, I don't really have all that much
spare cash lying around to spend on this project or on a new monitor.

You guys have helped me already, particularly by mentioning the possibility
of arcing. I have a good multimeter and I can get my hands on an
oscilloscope if I need to. If it is about arcing though, I'd imagine that in
the best case scenario the whole problem can be fixed by a piece of
insulating tape somewhere.

Please do let me know if you have any further suggestions.
--

Arto Rantala

"Arto Rantala" bravely wrote to "All" (19 Mar 05 11:59:02)
--- on the heady topic of " Hitachi CM813ET image jitter"

AR From: "Arto Rantala"
AR Xref: aeinews sci.electronics.repair:43408

AR Thank you for your replies, Asimov and Jerry,

You discussed vibration as not affecting the problem but many devices
may have heat sensitive internal joints which are not very sensitive
to vibration by comparision to cold solder joints. Among these are
electrolytic caps, resistors, transistors, IC's, etc.
AR True. My intention is to at some point open the case and use cold
AR spray to find any such heat sensitive components. There are, however,
AR a lot of components in a monitor, making it rather difficult to just
AR start spraying around, which is why I would have been interested in
AR learning of any starting spots anyone could suggest.

Basically this symptom mimics what arcing would do, which is to inject
high voltage glitches into the horizontal output section. Other
circuits that handle high voltages are the focus and screen controls.
If one of these has an intermittant contact it would seem like arcing
too. Same thing with the neck board crt socket since this carries the
actual voltages to the tube and any intermittant here would also seem
like arcing. Clean the crt pins with a plastic scotchbrite pad.
Similarly the wire connectors on the main board for these voltages may
be iffy. Even the crt high voltage cup is a suspect, clean and use
dielectric grease to seal the air out of the high voltage rubber boot.
Don't forget to discharge the crt first just in case!

Check the solder joints at the HOT and especially the base drive.
Check specifically any small pulse shaping inductors in the base drive
for signs of glue in the legs. Remove old solder clean inductor legs
and pcb holes thoroughly and re-install with fresh solder.

If the yoke socket pins have shiny solder and generally looks good,
not dull grey, then I would definitely suspect electrolytic capacitors
next due to the age of the monitor alone. Replace those in areas close
to sources of heat such as heatsinks or power transistors. Replace
those which handle substantial power such as derived supplies. Suspect
anything that looks off colour or bulging, leaking, etc. After the
electros are tested for esr/value/leakage or replaced then proceed
next with testing zener diodes used for reference. Prod suspect parts
with a long plastic wand to provoke the symptoms. Use freeze spray,
etc.

There aren't that many small components in the horizontal output
section that each can't be replaced until the bad one is found.
There is a finite limit of parts after all.

A*s*i*m*o*v

.... :) What does that wire do? =3d8Q (oh!)

Asimov wrote:
Basically this symptom mimics what arcing would do, which is to inject
high voltage glitches into the horizontal output section. Other
circuits that handle high voltages are the focus and screen controls.
If one of these has an intermittant contact it would seem like arcing
too. Same thing with the neck board crt socket since this carries the
actual voltages to the tube and any intermittant here would also seem
like arcing. Clean the crt pins with a plastic scotchbrite pad.
Similarly the wire connectors on the main board for these voltages may
be iffy. Even the crt high voltage cup is a suspect, clean and use
dielectric grease to seal the air out of the high voltage rubber boot.
Don't forget to discharge the crt first just in case!
a lot of other useful information

Now this is what I came here for, and then some! Thank you Asimov. Now I
have something very concrete to go by. If you ever visit Finland, look me up
and you shall not be short of beer.

--

Arto Rantala