EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Charlie86 on April 21, 2018, 01:37:03 pm

Title: Samsung 2433bw
Post by: Charlie86 on April 21, 2018, 01:37:03 pm
Hi,

I am trying to repair LCD monitor Samsung 2433BW,

Monitor works fine for lets say 1h then backlight goes of, usually if I turn it off and on again it works again. Sometimes it just flick backlight for second or two and then works well again.
I was assuming bad caps so I replace all except big one 120microFarad 450V, but this one is for power not for backlight,.. Board is also a bit black because of overheating. Pics are in att. I am now assuming bad transformer inverter or transistor. Can some one please give me advice how to test for bad components. I have oscilloscope and multimeter bad not enough knowledge to test them.

Thank you and have a nice day.
Title: Re: Samsung 2433bw
Post by: oldway on April 21, 2018, 01:52:02 pm
Quote
Board is also a bit black because of overheating.
Reflow this region adding flux and new solder.
Title: Re: Samsung 2433bw
Post by: LateLesley on April 21, 2018, 07:22:55 pm
could we get a picture of the underside of the board? I'm betting there's some circuitry underneath (probably a backlight controller and a couple of SMD FETs, along with a load of passives), which could be overheating. It might need a couple of new fets, i've had them burn up in monitors before. I usually replace them, and add some thermal pad to heatsink them to the chassis, to save them from dying again.
Title: Re: Samsung 2433bw
Post by: wraper on April 21, 2018, 07:31:08 pm
Most likely not cause of the current issue but you used unsuitable capacitors. Samwha RD are general purpose series and will fail maximum in a few months of use. Check both secondary windings of CCLF transformer, they should measure around 1k and match closely. Also check blue capacitors connected to secondary windings of CCFL transformer. CCLF lamp may be going bad as well. Not that bad that it does not completely work but bad enough to cause protection eventually kicking in.
Title: Re: Samsung 2433bw
Post by: wraper on April 21, 2018, 07:36:07 pm
Quote
I have oscilloscope and multimeter
Just don't connect them to secondary windings of CCFL transformar while monitor is switched on. High probability to destroy them due to 600V+ voltage. Also don't touch primary side of PSU with oscilloscope. Many people unaware that oscilloscope probe is grounded got expensive lesson.
Title: Re: Samsung 2433bw
Post by: wraper on April 21, 2018, 07:42:08 pm
Quote
Board is also a bit black because of overheating.
Reflow this region adding flux and new solder.
Dangerous suggestion, especially for people who have hot air, as phenolic PCB will most likely popcorn if heated with hot air. One might look for cracked solder joints of through hole components and resolder anything suspicions. But suggestion of reflowing everything is not very wise.
Title: Re: Samsung 2433bw
Post by: Charlie86 on April 22, 2018, 07:26:31 am
Hi,

I currently do not have pic of other side of PCB because, I resolder cold joins of transformer and assembly it back in housing of monitor. For now monitor is working. I think "oldway" have a point here :)

Thank you!