Samsung PN50A400

[tvguy616]

Hello,

First tv fix attempt. Got it off craigslist for a deal and hoping I can get it working.

I have read some threads and found some information on the boards and the general operation of the tv.

The tv has no display but does have sound. The screen does power on to a backlight state but displays no image or any sort of menu when using the remote. The screen will flash dark and then back to the backlight state when pressing buttons such as source, menu, tools, ect.

First diagnosis was the Y SUS but starting to second guess myself. Fuses in both the X and Y SUS were good.

I tried unplugging the X and Y SUS individually (after power down and wait time for discharge). X sus unplugged still had sound but no backlight and y sus yielded the same result as the X. This test along with the fact that both fuses in the boards were in fine shape, lead me to believe that my problem lies somewhere else.

Moved onto the logic board next. It also looks good. Has a flashing green LED that flashes once every second (im pretty sure this is normal from my findings).

Was hoping someone could point me in a direction of where to look next. I really don't want to just throw a bunch of parts at it.

[tom66]

Re: Samsung PN50A400

Do the logic board test pattern test here:
https://www.badcaps.net/forum/showpo...61&postcount=2

If you get good test patterns, your main board is at fault. You can decide to repair or replace but most main boards would be replacement jobs due to the firmware problems which typically affect them and cause this fault.

[tvguy616]

Re: Samsung PN50A400

Just tried the logic board test. Same results as above.

[tom66]

Re: Samsung PN50A400

In which case, most likely (though not certain) you have a logic board or Va failure on panel drivers.

Along the bottom of the plasma panel, there are some thin boards which connect to the logic board. Can you get pictures of them? Usually, they have a fuse.

[tvguy616]

Re: Samsung PN50A400

Got the panel removed. Found the boards, did not find any fuses on them.

I attached some pictures of the boards.

[tom66]

Re: Samsung PN50A400

I can see a little white surface mount fuse next to the connector coming off the Y-main, can you get a closer picture around this area? Do not unplug/replug this connector.

[tvguy616]

Re: Samsung PN50A400

It does appear to be a fuse. Good eye!

Text notes fuse being a 5al/125v. Looks to not be burnt up.

[tom66]

Re: Samsung PN50A400

OK, set powered on, screen glowing, test voltage from each end of this fuse to chassis ground. Expecting around 55~60V both sides.

You will need a digital multimeter.

[tvguy616]

Re: Samsung PN50A400

Will be picking up a dmm tomorrow from my parents house. Will have results tomorrow night.

Im assuming if I do see voltage on both sides of the fuse, then I will need to replace the logic board?

[tvguy616]

Re: Samsung PN50A400

Got voltages. One side is 92v other side is 12v. The 92 side is the one that comes right off the connector from the y sus.

[tvguy616]

Re: Samsung PN50A400

I just grabbed some more info off it with my dmm. This is all with the TV on.

Vs: 373, supposed to be 208
Va. 16, supposed to be 56
Ve. 160, supposed to be 100

[tom66]

Re: Samsung PN50A400

Set your voltmeter to the DC range, not AC. DC has a dashed bar and solid bar. AC has a squiggle like this ~.

[tvguy616]

Re: Samsung PN50A400

Those are all DC voltages. I used the settings in the upper left corner of my dmm as pictured.

[tvguy616]

Re: Samsung PN50A400

Just wanted to update this. After some heavy research ive found that the fuse in post 7 is a common fault with this series of TVs. Just replaced this fuse and tv is working perfectly!

[newtothis]

Re: Samsung PN50A400

For future info, The black lead goes to COM on your DMM.

Red will go to either of the top depending on the application in which it is being used.

This is why you were getting crazy readings

Not trying to knock you here but setting up a DMM is basic in electronics repair, Without it you wont get far...... So before you go jumping into another TV etc please do some basic learning on the tools you are using, difference between amps and voltage (its the Amps that will kill you) and basic troubleshooting guides. I say this as not knowing this stuff can be deadly!

Anyway well done on the repair

[freakaftr8]

Re: Samsung PN50A400

If this fuse iis a common occurance to blow on this set, I would suggest that there is a possibility of the fuse either being too low in amps or too much forward current inrush?

[tvtimmy]

Re: Samsung PN50A400

I read about the little white fuse on the bottom board where the y sus plugs in it on your super knowlegeable forum and I replaced it and the set is good to go! Thanks Bad Caps !