Monitor works on damaged inverter transformer, but doesn't on new (solved)

[AndreyS]

Monitor is Samsung P2250n.
It has QGAH02101 inverter transformer. I got the monitor with damaged transformer, in particular one coil is burnt and open (seen on picture).
On this damaged inverter transformer the monitor works fine, except it stinks as hell when on full brightness after 30mins.

I've bought new inverter transformer. And monitor just turns off after about 2 seconds.
What I've done so far, but didn't helped:
1) All caps are replaced.
2) I tested with external 16V and 5V power supplies.
3) The display has 2 pairs of connectors, which go into two coils of inverter transformer. On old transormer, only one coil is used (effectively). I connected one pair to non-damaged coil and then the other pair. In both cases monitor worked fine (except of the stink after some time). This concludes the actual display is not a culprit.

Source of the stink is the inverter transformer.

Why does monitor turn off after ~2 seconds. How to fix that?

[AndreyS]

Schematic for the monitor's power supply
https://ia801209.us.archive.org/21/items/Samsung_BN44-00296A/Samsung_BN44-00296A.pdf
Transformer I've bought https://www.aliexpress.com/item/1PCS-QGAH02101-02101-A09TM48A-LCD-high-voltage-coil-step-up-transformer/32806740075.html
The coils have ~1085 Ohm each. The coil from the old transformer has ~1125 Ohm. Can it be the cause? Maybe tweaking some resistors would resolve the problem?

Markings on the old damaged transormer are QGAH02101 A09TM33A. On new one are QGAH02101 A09TM48A

[perieanuo]

magnetic properties are the issue, resistenve says almost nothing. it's just the wrong transformer. And I always buy 2 or 4,after some time anotherone will dye
regards, pierre

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[duak]

I used the same basic part (QGAH-02101) to repair a Samsung 2233 but didn't have any trouble - it worked fine.  I think the other letters and numbers on your transformers are a batch or date code.  Those resistance values are quite close, and the difference is in the right direction ie., less resistive loas.

Did you replace both C20 and C54 and, if so, did you use low ESR replacements? I wonder if the +16V supply can no longer supply enough current for a fully functional backlight transformer.

There are a number of capacitors, resistors and diodes in series with the backlights (connectors CN71 & CN72) that detect the voltage applied to and the current drawn by them.  IC41 determines if these are correct and if not, shuts itself off.  I would check these components to see if any were bad.  I believe the data sheet for the IC is available.  I'm surprised the damaged transformer partially works, so there might be an unusual combination of other component failures.

Cheers,

[AndreyS]

Today, I managed to successfully repair that monitor. The problem laid in transformer indeed. I had ordered 2 transformers from different suppliers. One had 1050 Ohm resistance secondary, the other one had 1130 Ohm. And the latter worked