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Old 01-13-2021, 05:28 PM   #1
bianchi77
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Default Samsung SyncMaster740N ?

Dear Members,

I have Samsung SyncMaster740N ,
I replaced 12V and 5V rail capacitors about 5 years ago,
now the symptom is,

it turns on few seconds, then black screen but power still on,
what could be the cause ?

Thanks

Last edited by bianchi77; 01-13-2021 at 05:30 PM..
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Old 01-13-2021, 08:40 PM   #2
redwire
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Default Re: Samsung SyncMaster740N ?

It sounds like the CCFL backlight IC is shutting down. They turn on the backlight, if it detects abnormal current, such as open tube, arc, bad connection they shutdown after a few seconds.
See if both tubes are lighting up when it starts. The inverter output disc capacitor can fail as well, or the tubes can be really old with blackened ends.
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Old 01-14-2021, 03:30 AM   #3
bianchi77
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Default Re: Samsung SyncMaster740N ?

Quote:
Originally Posted by redwire View Post
It sounds like the CCFL backlight IC is shutting down. They turn on the backlight, if it detects abnormal current, such as open tube, arc, bad connection they shutdown after a few seconds.
See if both tubes are lighting up when it starts. The inverter output disc capacitor can fail as well, or the tubes can be really old with blackened ends.
Where can I see " if both tubes are lighting up when it starts"
May be I need to replace the tube, because it was flickering before it blank out.

Is the tube for this model easy to find ?

Thanks
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Old 01-14-2021, 09:14 PM   #4
redwire
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Default Re: Samsung SyncMaster740N ?

Check the replacement capacitors are still OK, they might have died after 5 years, if they were not top brands.

In a dark room, you can see backlight bleed-through and the tubes run across the top and bottom edges. There should be some glow along the two edges until the IC safety mechanism "2 seconds to black" trips.
If you can navigate the OSD, changing the brightness up can also give more to an old tube and it might run.

CCFL Warehouse shows you what is available, LED conversion kits too but they have premium pricing. eBay and Ali have the tubes too, they go by the inch I believe.
https://lcdpartsdirect.com/product/4...creen-monitor/
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