need help with odd CRT monitor image

ern, the image starts out perfectly at the top. as you move down toward the middle , it gradually starts to compress the image, with more compression the closed you get to center. and when it gets to mid screen, its a full v ertical collapse. bright while line across the center, with no image whats oever in the lower 50% of the screen. also sold as a vision pro .

flyback.

n 2 ( output) is a nice 24 v square wave. i recapped the monitor, and the image is exactly the same. now im stuck.

Sounds like a shorted turn in the deflection yoke, but not sure what you me an by a square wave on the output.

Your vertical circuit is missing the bottom deflection half of the vertical circuit. If the vertical driver is an IC, replace it, if it is a pair of transistors then I would suspect the transistor pulling to ground (typically the lower of the two on schematics) is the one at fault.

The vertical drive is just a very slow audio amp, apply audio amp service methods.

John :-#)#

And if it has a large value (1000-4700uF) cap inside the feedback loop that is failing, that can cause severe linearity issues.

that is failing, that can cause severe linearity issues.

Granted, however the OP did say he recapped the monitor and I didn't want to doubt his statement.

John ;-#)#

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that is failing, that can cause severe linearity issues.

its an IC, an LA7833( nte1773) . i'll change it out and see what happens. i did change out every cap, and it was exactly the same. no better, no worse .

thanks much

p that is failing, that can cause severe linearity issues.

i did change out every cap, and it was exactly the same. no better, no wor se.

just got done replacing the vertical IC, la7833. no change in the image. no better, no worse.

op that is failing, that can cause severe linearity issues.

ns. i did change out every cap, and it was exactly the same. no better, n o worse.

. no better, no worse.

Any schematic you can provide a link to? Someone suggested a bad yoke, which is possible if the bottom half of the vertical deflection shorted out. Maybe. However a schematic would help.

John :-#)#

Looks like the 24 volt supply is generated by doubling the 12 volt supply. Measure the 24 volt supply at pin 6. I bet something is wrong that this is only 12 volts, maybe the diode?

op that is failing, that can cause severe linearity issues.

ns. i did change out every cap, and it was exactly the same. no better, no worse.

. no better, no worse.

is

B+ is 12v3, 12V and 24V good. i was thinking yoke, but they ohm out good, a nd look like brand new. no physical damage. looks like a few transistors a re after the vertical ic, i'm looking at them now. not real good at follow ing this schematic, so any help is appreciated.

thanks

I'm not so good at following this schematic myself. It looks like W402 is the connector to the yoke. If so, I would say Q404 sets the vertical position. Q360 and D307 link the vertical drive signal to I201, the color gun controller. Perhaps this is creating too large a load from a bad part, so the drive is clipped?

Did you say I302 pin 2 has a square wave on it? Shouldn't that be a sawtooth?

nual.pdf

hematic.pdf

and look like brand new. no physical damage. looks like a few transistors are after the vertical ic, i'm looking at them now. not real good at foll owing this schematic, so any help is appreciated.

In the yoke there are two coils for vertical and two for horizontal connect ed in series or parallel depending on the design, if in parallel one coil c onnection could be broken. The coils are connected together in the solder p osts on the yoke, you may check there if some wire looks loose.

manual.pdf

schematic.pdf

d, and look like brand new. no physical damage. looks like a few transisto rs are after the vertical ic, i'm looking at them now. not real good at fo llowing this schematic, so any help is appreciated.

cted in series or parallel depending on the design, if in parallel one coil connection could be broken. The coils are connected together in the solder posts on the yoke, you may check there if some wire looks loose.

thats a great idea, i didnt know the coils were doubled up. i will check th at for sure tonite. i was thinking of inverting the image, there are solder pads for an inverted header on the chassis board, and see what the image d oes. that would tell me if its the yoke or a chassis issue. does that make sense?

thanks much

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loop that is failing, that can cause severe linearity issues.

pens. i did change out every cap, and it was exactly the same. no better, n o worse.

ge. no better, no worse.

ly.

s is

nual.pdf

hematic.pdf

and look like brand new. no physical damage.

Not saying the yoke is the problem, but a single turn shorted to an adjacen t turn will not change the resistance reading on your dmm, but a single sho rted turn will totally collapse the magnetic field of the coil.

A ringer is the best instrument to check for shorted turns.

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k loop that is failing, that can cause severe linearity issues.

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appens. i did change out every cap, and it was exactly the same. no better, no worse.

mage. no better, no worse.

pply.

his is

manual.pdf

schematic.pdf

d, and look like brand new. no physical damage.

ent turn will not change the resistance reading on your dmm, but a single s horted turn will totally collapse the magnetic field of the coil.

not sure what a ringer is, but im pretty sure i dont have one. you mean lik e a tone generator, and you move it around the yoke ?

Not quite - it has flyback boost and tailored feedback for linearity.

Either of those can cause similar symptoms.

There might be a flyback diode lurking nearby - it could've gone leaky.

DSE did one, but I don't think the kit is available anymore.

The schematic is floating about and there's no unobtanium in the parts list.

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ack loop that is failing, that can cause severe linearity issues.

idn't

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happens. i did change out every cap, and it was exactly the same. no bette r, no worse.

image. no better, no worse.

supply.

this is

ood, and look like brand new. no physical damage.

acent turn will not change the resistance reading on your dmm, but a single shorted turn will totally collapse the magnetic field of the coil.

ike a tone generator, and you move it around the yoke ?

A dedicated instrument that checks inductors for shorted turns by injecting a waveform and counting the "rings" (like echos). A shorted coil won't ri ng or will ring very low. In the old days, several companies made "flyback " testers that would check flybacks and yokes for shorted turns. I have a Sencore LC75 that has a ringing feature and it works well.

Another way of checking the yoke out of the circuit can be done with a scop e. If you can identify and electrically separate the two halves of the vert ical yoke, you can connect each section to the calibration output jack of y our scope and monitor the resulting waveform of each. Unless the top secti on shorted to the bottom, you can be pretty confident you have one good sec tion and one bad. If the waveform on one of the sections is severely distor ted compared to the other, it's a yoke issue. If both waveforms look the s ame, the yoke is most likely good.

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The old DS ringer was designed by Bob Parker and was best for checking flybacks (LOPTs), not much use on yokes I'm afraid. The kit is now made by Anatek (we carry it on Flippers), but you would be better off with an

inductance meter - split the vertical windings and each side should be identical.

John :-#)#