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Old 09-15-2021, 08:28 AM   #1
falcontech
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Default BN44-00082F no backlight

Hello to all
I have a problem with this power board, it does not produce the backlight, I have the power led working but the monitor does not show signs of an image, when it stopped working I found the capacitor highlighted in red exploded but nothing else, I replaced it but the problem persists
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Old 09-15-2021, 03:22 PM   #2
lotas
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Default Re: BN44-00082F no backlight

Check out fuse F301 and here's a diagram to help you figure it out.
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Old 09-16-2021, 04:58 AM   #3
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by lotas View Post
Check out fuse F301 and here's a diagram to help you figure it out.
ok thanks is the fuse broken, do i need to check something else before replacing it?
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Old 09-16-2021, 06:53 AM   #4
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Default Re: BN44-00082F no backlight

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Originally Posted by falcontech View Post
ok thanks is the fuse broken, do i need to check something else before replacing it?
Check diodes, transistor assemblies, zener diodes for a short circuit ...
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Old 09-21-2021, 07:07 AM   #5
falcontech
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Default Re: BN44-00082F no backlight

I finally replaced the fuse that I had to order, there is still something wrong the lamps do as if to turn on but they can't, they flash as if it were a stoboscopic light, what could it still be?
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Old 09-21-2021, 07:18 AM   #6
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Default Re: BN44-00082F no backlight

I realized that when this event occurs, the power LED also flashes as if there were some exhausted electrolytic but nothing is visible on sight, in addition to replacing the exploded one I also replaced the largest one but the situation has not improved

Last edited by falcontech; 09-21-2021 at 07:40 AM..
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Old 09-21-2021, 05:12 PM   #7
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Default Re: BN44-00082F no backlight

What equipment to you have for repairing electronics? You can't just LOOK at capacitors to determine if they are good or bad. Start by replacing, the small caps, C123 & C235. Then check the secondary voltages +13, +5.1 , are they correct and stable
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Old 09-21-2021, 05:40 PM   #8
falcontech
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Default Re: BN44-00082F no backlight

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Originally Posted by R_J View Post
What equipment to you have for repairing electronics? You can't just LOOK at capacitors to determine if they are good or bad. Start by replacing, the small caps, C123 & C235. Then check the secondary voltages +13, +5.1 , are they correct and stable
the equipment I use is that of an amateur, I can measure well or badly All the components and substitutes, mine was only a consideration to say that there was nothing out of the ordinary, thank you for the advice I will do what I do you asked for thanks
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Old 09-22-2021, 08:32 AM   #9
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by R_J View Post
What equipment to you have for repairing electronics? You can't just LOOK at capacitors to determine if they are good or bad. Start by replacing, the small caps, C123 & C235. Then check the secondary voltages +13, +5.1 , are they correct and stable
I replaced the capacitors yourself as a precaution and the voltages are perfect at the output, I noticed that when I give current you can hear a hiss from the power supply intermittently which coincides with the flashing of the lamps
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Old 09-22-2021, 07:07 PM   #10
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Default Re: BN44-00082F no backlight

Check the 4 small blue caps (C324 etc.) for cracks, if they are ok, check the transformer secondary resistance and compare the resistance between the two secondary's. The hiss may be coming from the high voltage transformer OR it may be due to a bad ccfl (cracked lamp in the panel)

Do you get a flash of the backlights? If you do, unplug all the ccfl lamps, then try only connecting one lamp, if you get a flash of the backlight, unplug that lamp and do the same for the next lamp, do it for all for lamps, a bad ccfl likely will not light.

Last edited by R_J; 09-22-2021 at 07:11 PM..
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Old 09-23-2021, 12:35 PM   #11
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by R_J View Post
Check the 4 small blue caps (C324 etc.) for cracks, if they are ok, check the transformer secondary resistance and compare the resistance between the two secondary's. The hiss may be coming from the high voltage transformer OR it may be due to a bad ccfl (cracked lamp in the panel)

Do you get a flash of the backlights? If you do, unplug all the ccfl lamps, then try only connecting one lamp, if you get a flash of the backlight, unplug that lamp and do the same for the next lamp, do it for all for lamps, a bad ccfl likely will not light.
is the transformer whose resistance I have to check is the high voltage transformer of the lamps? the hiss that is heard does so even without connected lamps, the lamps one at a time I had already tested them and nothing changes
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Old 09-23-2021, 10:15 PM   #12
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by falcontech View Post
is the transformer whose resistance I have to check is the high voltage transformer of the lamps? the hiss that is heard does so even without connected lamps, the lamps one at a time I had already tested them and nothing changes
Check the resistance of T301 secondary, this is the transformer that produces the high voltage for the lamps.
Is this where the hiss seems to be coming from?
In some cases those small blue disc caps have shorted and burned, it may be that one of them is arcing internally causing the hiss.

Last edited by R_J; 09-23-2021 at 10:18 PM..
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Old 09-24-2021, 06:43 AM   #13
falcontech
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by R_J View Post
Check the resistance of T301 secondary, this is the transformer that produces the high voltage for the lamps.
Is this where the hiss seems to be coming from?
In some cases those small blue disc caps have shorted and burned, it may be that one of them is arcing internally causing the hiss.
that noise comes from the opposite side of the transformer of the lamps (near the transformer smps), it is as if a machine tried to start but without making it, I measured the resistance of the secondary as you told me and they are identical to each other, as I wrote in precedence when the lamps are flashing the power led of the monitor also flashes and this flashing follows that hum you hear

Last edited by falcontech; 09-24-2021 at 06:45 AM..
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Old 09-27-2021, 07:17 AM   #14
falcontech
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Default Re: BN44-00082F no backlight

Quote:
Originally Posted by R_J View Post
Check the resistance of T301 secondary, this is the transformer that produces the high voltage for the lamps.
Is this where the hiss seems to be coming from?
In some cases those small blue disc caps have shorted and burned, it may be that one of them is arcing internally causing the hiss.
I replaced the ceramic capacitors and the lamps and still nothing same problem
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Old 09-28-2021, 11:27 AM   #15
falcontech
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Default Re: BN44-00082F no backlight

another thing I noticed while taking measurements is that on a bigger capacitor I have 328 volts and I think it is right, on the one circled in red in the photo (the first one replaced) I have scarce 15 volts, I don't know if the voltage that reaches it is exact, the capacitor is 35 volts
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Old 09-28-2021, 07:03 PM   #16
R_J
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Default Re: BN44-00082F no backlight

The main cap C114 should have 328 volts, so that is ok. I don't understand
Quote:
I have scarce 15 volts
Do you mean +13 volts?
If C301 was "exploded" you may want to replace C261 as well as it is on the same line. Maybe C235 is bad.

Last edited by R_J; 09-28-2021 at 07:17 PM..
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Old 09-29-2021, 08:08 AM   #17
falcontech
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Default Re: BN44-00082F no backlight

as I said earlier I have already replaced all the electrolytics, the doubt arises that it could be the bd9893f, what should the voltage on the electrolytic be blown? as I told you I measured about 15 volts, its capacity is 680uf 35v
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