Samsung 721N LED blinking quickly

[mirkoslav]

I've tried searching the forum but couldn't find a similar thread so please excuse me if this has been asked before - I'm new here.

Replaced two 2x820uF and 330uF caps in my Syncmaster 721N, but it won't power up. The power LED is blinking at a fast pace, and the power supply sounds like it's trying to power up repeatedly, only to have it shut down by some over-voltage/over-current protection system. The sound is barely audible and high pitched, but it's there.

Did anybody encounter a similar problem (fast blinking LED)? Please advise where to look regarding this specific problem.

Thanks!

[selldoor]

Re: Samsung 721N LED blinking quickly

Read this: https://www.badcaps.net/forum/showpo...&postcount=204

Sounds like your problem - test the two components mentioned



Welcome to the forum-
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back (in the same orientation) and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attachm...1&d=1290283049

https://www.badcaps.net/forum/attachm...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.

[mirkoslav]

Re: Samsung 721N LED blinking quickly

Sounds like your problem - test the two components mentioned
...
It will be useful if you can say a bit about yourself - skills tools etc.

Thanks for the quick response, I'll check/measure those. I didn't run anything unplugged and nothing looks burned, but it still sounds plausible since something is probably short-circuiting the power supply output. Will try to take some pictures and post them.

I have some background in DIY electronics and know how to solder, so I think I could try any fix required.

[selldoor]

Re: Samsung 721N LED blinking quickly

Sorry - I think its just the one component ( U205 component with SP8M5) I read it at first as two separate items.

[mirkoslav]

Re: Samsung 721N LED blinking quickly

Update: monitor is fixed! In case anybody encounters a similar issue in the future, the problem was indeed the H-bridge MOSFET. It short-circuited, tripping the overcurrent protection and causing the power supply to keep power cycling. After replacing it with a good one, the display came alive and it's working again. Thanks for your help!