Sharp Image 34" Magnetic Interference [PICS ADDED]

[Arm123]

Hey there Guys.

I have a Dynamo showcase cabinet that I was preparing for a 60 in 1 installation.  The monitor is a Sharp Image chassis with a 34" Sony Trinitron CRT.

The image was nice, except for a slight discoloration of the top right corner of the screen, that looked like magnetic interference.  Moving the monitor around my garage made it clear up a bit.  So I guess its fair to say I have some sort of magnetic interference in my work area.  I have never noticed this before when working on smaller 13" touch screen monitors.

So i proceeded to flip the monitor vertically.  To my surprise, the interference was ALOT worse once flipped !

I moved the machine all over the place and observed the magnetic interference color bands clear up in some spots and but appear in others. I found this very odd.

I have a couple of questions...

Don’t these larger monitors have a pot to adjust for the magnetic interference of the earth ?

What’s the x-ray control pot do ?

Are larger monitors more susceptible to magnetic interference ?

[qrz]

turn an operating crt on it's side and the pic Will be discolored until the screen is deguassed.

on ur cab, if the internal deguassing coil does't do the trick when in final position , an external coil may need to be used.

the change in position relative to earth's magnetic field alters the electron passage through the crt's shadow mask
thus strinking an incorrect phosphor dot ( producing a wrong color).
stray magnetic fields (unshielded  speakers a common offender ) can produce the same effect

crt X-ray protection is present because x-ray radiation can be produced with excesive high voltage .
the voltage default level is factory set ( DO NOT ALTER POT )
typically, if hv exceeds 32kv, the horiz osc shutsdown . no hv is produced at this point and can't be restarted .
the monitor will be inoperative until deactivated ( pwr removed ) reseting the detector.
of course the circuit will retoggle if there is a fault .  ( typically a voltage regulation issue )


qrz

[Arm123]

turn an operating crt on it's side and the pic Will be discolored until the screen is deguassed.

on ur cab, if the internal deguassing coil does't do the trick when in final position , an external coil may need to be used.

the change in position relative to earth's magnetic field alters the electron passage through the crt's shadow mask
thus strinking an incorrect phosphor dot ( producing a wrong color).
stray magnetic fields (unshielded  speakers a common offender ) can produce the same effect

crt X-ray protection is present because x-ray radiation can be produced with excesive high voltage .
the voltage default level is factory set ( DO NOT ALTER POT )
typically, if hv exceeds 32kv, the horiz osc shutsdown . no hv is produced at this point and can't be restarted .
the monitor will be inoperative until deactivated ( pwr removed ) reseting the detector.
of course the circuit will retoggle if there is a fault .  ( typically a voltage regulation issue )


qrz

Thanks qrz...

I haven't messed with the x-ray pot, but its not glued into position.  So there is a possibility that it could have been played with by another person.  I hope I'm not getting more than my normal dose 

The whole cabinet is on wheels and i can move it around.  The image changes when i move it in different places.

Also, when the monitor was mounted horizontally, i removed the speakers to make sure it wasn't the cause of the interference.  The image was the same with out them.

I sure hope its nothing internal. Ill have to play around again tomorrow.

[grantspain]

perhaps its just the degauss circuit not working,if so it could be just the ptc

[Arm123]

I spent the day wiring this machine up and getting it ready for the 60 in 1 board.

I hit the degaussing switch on the breakout board a couple times and the coil does work, but doesn’t clear up anything.  Here are a couple pics from the 60 in 1 test menu.



Same picture after moving the cabinet around a bit.



You can see that the image changes.  I’m sure it must be some magnetic interference from wiring in the ceiling.  Although, I have had other arcade machine in my garage with out any of these troubles.  So Ill have to move it some place else to test my theory.

Also, I decided to pull the chassis and look at it.  Here is what it looks like...



It looks as if the flyback has been changed and a couple other components.  However you can see that the tech also did this mod on the traces around the flyback...  Not sure why ?  Was it perhaps to get a flyback that wasn’t an exact pin out match, to work on this chassis ?

Also, I noticed this when looking at the components...



D901 is supposed to be a CGJ-1 which is a 1500v, 2A fast recovery diode.  In its place is a 'coupled' D07-15 which is a 1300v -to- 1500v, 1.5A

Why do this ?  Could this tech not find the right part and decided to couple them ?  Would this mod allow the diode to take the voltage ?

This is purely for information purposes, because i plan on replacing it with the right part.

[Arm123]

Well… I pulled this monitor and put it on the floor horizontally. The colors wee fine, except for some very slight discoloration on the right side. This cleared up with warming up and a degauss.

I readjusted the conversion and purity rings for the hell of it. After 45 min of playing, the image does look sharper / more accurate now.

Then I decided turn it off and flip it vertically. Same BS happened with the colors. Crazy inverted colors all over the place and degaussing didn’t help. For the hell of it, I decided to flip it the opposite (upside-down) way vertically. It vastly improved the color distortion. Only the top left corner and bottom right were messed up (RED). I cant seem to get ride of this.

Now, I must say that the image is very nice on this monitor when its working properly. Trinitron tubes are great but it appears that this thing does not want to go vertical.

I have done everything that I can think of, in short of replacing that fly back and diode mod. Would that cause these types of discoloration and vertical problems ?

[qrz]

older trinitron crts' had external magnetic shielding as they were sensitive to stray fields......
part of the issue is that a trinitron crt uses an aperture grill ( supported by fine wire- # determined by screen size )rather than a shadow mask.

see here for crt info:  http://www.repairfaq.org/sam/crtfaq.htm

qrz

[Arm123]

Thanks qrz.

Iv been threw that document before.  I guess this menas that i cant have the Trinitron CRT in my 60 in 1 cabinet.  I guess ill have to switch it out with another show case cabinet it have.  Kind of sucks cuz this monitor looks great.

[qrz]

try a manual deguassing before giving up on the tube.

run the coil front, back ,sides..,  this way an' that ......be persistant,  it may yet work for ya  ...?

several summers ago, i had to do just that on a couple of sony's w/storm damage .
a nearby lightning strike had even magnitized the shielding ... 
took multiple attempts to clear it.

qrz

[Arm123]

try a manual deguassing before giving up on the tube.

run the coil front, back ,sides..,  this way an' that ......be persistant,  it may yet work for ya  ...?

several summers ago, i had to do just that on a couple of sony's w/storm damage .
a nearby lightning strike had even magnitized the shielding ... 
took multiple attempts to clear it.

qrz

Leaving the monitor mounted in the cabinet, i used a manual deguassing wand / coil.   The first couple of trys cleared it up a bit.  Then i started focusing on the corners and it totally cleaned up the left side !  I spent a while trying to do the right side with some substantial improvment.  However, its not totally cleared up and still noticable on the bottom right.

I didnt go threw the back and sides of the monitor because i wanted to check back here before i did that. I spent about 10 min total on this.

What should i do ?  Should i take the monitor out of the cabinet and proceed to do the sides and back of the tube ?


Thanks for your help qrz   

[grantspain]

using the manual degauss,have you tried switching off the cab and then starting in the middle of tube using a circular action move back from the tube

[Arm123]

using the manual degauss,have you tried switching off the cab and then starting in the middle of tube using a circular action move back from the tube

Hey there Grant, I just tried it a couple times and the problem still persists.  Although it is getting better.

I wonder if i should unmount the monitor and try it ?

[grantspain]

i did have a similar prob many years back whereby the fixing bolts became magnetised,obviously no speakers nearby

[Arm123]

i did have a similar prob many years back whereby the fixing bolts became magnetised,obviously no speakers nearby

I did remove the speakers and still the problem was there.

What ill do is unmount the monitor and put it on the floor.  Then im going to remove the mounting bars and bolts.  See what happens.

Thanks for the input