Bad computer monitor...

Shorted turn in the yoke?

Hi, thanks for replying.

I pulled the 4-pin connector off the circuit board, the Blue and Red wires make one loop, they are reading 0.7 ohms, the Yellow and Brown wires make the second loop, they reading 7.6 ohms.

I'm assuming and the 0.7 ohms on the red and blue wires is not normal. All four wires feed into a closed module sitting on top of the neck of the CRT. I'm going to open this (if possible without destroying it) and see if the source of the burning smell was coming from inside it.

The bottom of it's circuit board is visible, there are schematic symbols of resistors, etc. silk screened onto it.

More later...

-Landon

I haven't done this for 40 years, but the ratio isn't abnormal. A shorted turn would barely make a difference in resistance - you really need an inductance meter or another yoke or other to test it. Ohms alone isn't much help.

Hi JR,

Sorry, I have broadband, file size doesn't mean much to me anymore. Plus with things like this I would rather keep the image quality good so that details stand out.

-Landon

Hi Homer,

I don't have either, plain old digital multimeter is all that I have.

-Landon

Even a scope would help. Damn hard to fix with a DMM unless you have a lot of experience. Still, look over the board also for burned parts. Something made that smell.

Hi again,

I have looked the whole board over and can't find anything burnt, I was able to get that module open, it looks fine too. Everything in the high voltage section is covered in dust (which is the norm), I'm going to blow it out tomorrow with 120psi compressed air and then look things over again, something might be cracked.

The smell could have been coming from an overheating transistor, but after three days I would have thought that it would have failed, and not just cause a display malfunction. My best guess at this point is that a shorted capacitor is pulling the voltage down to the horz. section.

There are a hand full of solder joints in the high voltage section that look questionable too, will deal with that tomorrow as well.

Later,

-Landon

Caution!: '120psi compressed air' is enough to literally blow some components right off the board...depending on the nozzle you use. I'd suggest vacuuming first, using a paint brush to loosen the dust. Then use the compressed air *sparingly* to get at the hard parts.

Especially if the dust is thick, you could damage something hiding underneath it...

jak

Maybe use caution too with any "moisture" in that "compressed air". Use a "FILTER"......... I'd go with the other guys, be careful..............

On Tue, 03 Oct 2006 09:17:31 -0500, jakdedert Has Frothed:

Well he will find poorly soldered components with 120PSI. Also compressor air has oil and moisture aerosols in it unless it has a painter's filter and drip installed.

There should be at least one part that suffered from thermal abuse,.

The geometry correction has a faulty part .........

or it doesn't get a signal because the processor doesn't get the input, cannot handle it on, or it cannot be obeyed. The monitors I know have some of this circuitry towards very the front of the board, right under the CRT, very unaccessible without taking the board out :-(.

Best wishes, H.

check your caps on the horizontal side of the deflection yoke.

I had a viewsonic P775 do that stupid shit, but it would also take out the HOT after a bit. turned out to be a couple of those notorious blue HV caps.

I follow what the rest are saying. a scope would be very handy in this situation. you could easily see overloading in the output waveform if the yoke is shorted.

but one thing I noticed too is the raster is awful bright.

Hi Mike,

The raster is very bright because I turned the SCREEN adjuster knob next to the flyback transformer up so I could see where the edges of the scan lines were actually at. At it's normal setting the screen is black with the little "check signal" window in the middle.

After it appears on the screen 4 or 5 times the monitor goes into sleep mode, the high voltage shuts down and then you can hear the static crackle as all the dust looses its static charge. If you turn the monitor off/on or hit one of the adjuster buttons it comes right back on.

Right now it is not hooked up to a PC, so all it will do is the "Check signal".

-Landon

Heh, he'll find them somewhere on the other side of the room.

For the OP, if you dont know where to look a good starting point is to get a schematic with voltages marked on and check around the horiz scan to narrow it down. And check the various power lines, the horiz stage may provide power for various things.

NT

On Wed, 04 Oct 2006 09:24:11 -0700, meow2222 Has Frothed:

Yup exactly what I was thinking.

I don't remember the OP's technical level so arming him or her with technical lit may be as useful as giving a map to a blind man.

lj_robins ha escrito:

check any caps (usually rated 1kv or more) near where the horizontal coils from the yoke attach to the mainboard. something is wrong in the path to the horizontal yoke, (which may even have shorted turns but repalce the caps first).

-B.

Hi everyone,

Thanks for the replies from everyone, the problem turned out to be bad solder joints in the high voltage section near the flyback. Not sure which one did it, my suspicion is that the horz. output transistor had very little solder on one of the pins and that was what was causing the low voltage which caused the screen the shrink.

After re-doing every bad joint I could find the monitor works fine now, I left it on in display mode (not sleep mode) for 18 hours it still works fine.

Thanks again.

-Landon