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Crt monitor clicking sound and image shrinking and expanding in loop, can someone help ?

RadeMkd

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Hello,

Being a huge CRT fan, I poses several of them, but one of them just stopped working correctly.
So I was playing some games on it and when I switched resolution (it worked previously) it suddenly broke.
Now I have a clicking sound in loop (I think coming from the flyback) as well as a shrinking and expanding image horizontally.
It's like the monitor is turning and switching off in loop, a short in the circuit maybe ?
I checked some of the caps in the power area but they seem to be good. Visually, I cannot tell for a failed part.
Can someone help identify the problem, how should I proceed ?

Here is a link to a post I made on Reddit asking about the problem with video showing the problem.
 

Relayer

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Hello RadeMkd,
It sounds like your flyback transformer may possibly have shorted turns.
Your CRT anode voltage seems to be fluctuating.
What is the make and model of the offending set?
Regards,
Relayer
 

KlausST

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Hi,

I had similar effects on a Samsung TV.
--> Bad electrolytics capacitors in power supply.

A youtube video helped in my case to buy the necessary parts without opening the device.
Just try a search on youtube with your exact TV set type.

Klaus
 

RadeMkd

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It's a IBM e74
Type/Model: 6332-47N /C
FRU Part No: 22P7778
serial number: 66-NRC63
September 08 2001

Is there a way to test the flyback transformer ?
I think i will be able to dissolder it.
From what i read on the net if it's a short inisde it there is no way to repair it right ?
Would this mean it's game over for this crt since there are very slim chances i find a replacement part ?
Or will a salvaged flyback from another crt fit in ?

Also i tested every electrolytic capacitor on the board and they seem to be ok.

Thank you for your help.
 

Relayer

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Is there a way to test the flyback transformer ?
You would need a shorted turns tester. Though it wouldn't be a 100% test.
I would doubt you would be able to source a new transformer, though you might be
able to score a second-hand unit.

Or will a salvaged flyback from another crt fit in ?
No. It would have to be from the same make and model as the one you have.

You could try checking the horizontal output transistor, as that may be a possible cause.

Regards,
Relayer
 

RadeMkd

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You would need a shorted turns tester. Though it wouldn't be a 100% test.
I would doubt you would be able to source a new transformer, though you might be
able to score a second-hand unit.



No. It would have to be from the same make and model as the one you have.

You could try checking the horizontal output transistor, as that may be a possible cause.

Regards,
Relayer
I tested the HOT, i hope i did it correctly ?
From what i understand it should be ok ?
This are my results :
20201109_161029.jpg20201109_161033.jpg20201109_161134.jpg20201109_161137.jpg

A shorted turns tester is something that you construct yourself ?
Is there an other way to tell if flyback is faulty ?

It's realy strange because the monitor has low hours on it with perfect image and alignement.
It's the second monitor that goes faulty the same way "when changing desktop resolution" although the first one was in bad condition so i wasn't surprised that it broke.
As i said i have 4 crts left but i want to learn how to fix them when they go bad since they are becoming rare this days.

Regards,
Rade
 

Relayer

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I tested the HOT, i hope i did it correctly ?
Yes. Your test is basically correct. But you need to also perform a punch-through test.
Do this by setting your multimeter to it's highest ohms setting.
There should be on open circuit condition when measuring between the emitter and
collector both ways. i.e. black (negative) on the emitter and red (positive) on the collector
and vise-versa.
Also, with your black (negative) probe on the base and the red (positive) probe on either
the emitter or collector should also read an open circuit.

Is there an other way to tell if flyback is faulty ?
Unfortunately, no. A direct replacement would be the only way.

I'm actually at the point where your fault might be in the logic circuitry that controls resolution
changes. The blooming that's going on is possibly due to it falsely triggering in a loop.

Unfortunately it would be extremely difficult to diagnose anything without a schematic
diagram.

Sorry for the little help I can provide.
Regards,
Relayer
 

    RadeMkd

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RadeMkd

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I t
Yes. Your test is basically correct. But you need to also perform a punch-through test.
Do this by setting your multimeter to it's highest ohms setting.
There should be on open circuit condition when measuring between the emitter and
collector both ways. i.e. black (negative) on the emitter and red (positive) on the collector
and vise-versa.
Also, with your black (negative) probe on the base and the red (positive) probe on either
the emitter or collector should also read an open circuit.



Unfortunately, no. A direct replacement would be the only way.

I'm actually at the point where your fault might be in the logic circuitry that controls resolution
changes. The blooming that's going on is possibly due to it falsely triggering in a loop.

Unfortunately it would be extremely difficult to diagnose anything without a schematic
diagram.

Sorry for the little help I can provide.
Regards,
Relayer
I tested the HOT with the multimeter set to it's highest ohms setting and got this result on all tests :

20201110_202755.jpg

Unfortunately i can't find a schematic for my model on the internet.

This is a image of the board (it's not that big so it's less complicated i guess) :

20201110_091503.jpg

Maybe you can indicate where the logic circuitry that controls resolution is located on the board,
so i can go and test every component there (if i'm able ).

Thank you for your help which is more than good considering the little info you have :)

Regards,
Rade
 

Relayer

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Unfortunately i can't find a schematic for my model on the internet.
It would make it near impossible to repair without a schematic.

Maybe you can indicate where the logic circuitry that controls resolution is located on the board
See picture below:



I suspect this microcontroller shown within the green box does your resolution changes.
It's not as easy as hitting it with a logic probe as it would be meaningless.
See if you can get a part number off the IC and see if there's a datasheet on it. That may help.
Regards,
Relayer
 

    RadeMkd

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Relayer

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Datasheet
Unfortunately the datasheet is of no help.
The only way of seeing if that's the problem is to obtain another IC from another monitor
of exactly the same model.
Since it's a programmable microcontroller, you'd need an original from IBM and not the
manufacturer.

The only suggestion I have left to offer, is to obtain another second-hand monitor of the
same model on EBay or some other source. If you were to obtain one, you can easily just
swap parts from one to the other. Though I suspect that what you're encountering is a
known problem with this type of monitor.

Sorry that I cannot offer you more positive suggestions.
Regards,
Relayer
 

RadeMkd

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Sorry that I cannot offer you more positive suggestions.
Thank you for all your help.

I was looking for an identifier on the board and found that it's " C1770NSL".
There are other brands that used this same board on their monitors and i think i found the shcematics for it.
There is another person who had this same problem on his monitor but found no solution to it.
In one of his posts he speaks about x-ray protection kicking in loop.
Here you can read about it : link.

Schematics : c1770nsl.pdf.

Thank you for your suggestions
Rade
 

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RadeMkd

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Hello,

So i checked if the x-ray protection was kicking in and it isn't.
What i did next was to measure the G2 voltage.
I desoldered the G2 wire going to the neckboard and discovered that the voltage was too low around 20v-25v dc.
So now i'm realy suspecting a bad flyback.
That would explain the low G2 voltage as well as the clicking sound from the flyback.
Can anyone confirm what i think the problem is ?

Thank you.
Rade
 

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