"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!)