Samsung Plasma 50" TV PSU Issues

[stevefivey]

Hi, I'm having difficulty trying to trace my power supply problem. At one stage the TV's power LED was on and nothing else ( no picture, sound was ok tho ) now, there is no power at all ( no LED Power Light ). On the psu, the fuses tested fine and I am receiving 245v into the AC input. From the AC Input, I done a continuity test, the live side of the AC Input connects to a fuse ( fuse contact point ) and the neutral side of the AC input connects to another fuse contact point. With the fuses still out, I do a voltage test to both fuse contact points, on the neutral side I get 245v on the live side i get zero(despite there being a positive continuity test ). When I put the fuse in to the neutral side and leave out the fuse on the live side, I do a voltage check of the live fuse contact point, I get 245V on the opposite side of the contact point ( bridge ), when I put the live side fuse back in, and do the same voltage check, I get zero volts. There are no bulging capacitors or leaks, the board looks and smells fine, there is nothing obvious. I'm new to electronics, but really keen to learn and hopefully get this TV to work. Any help appreciated, cheers

 

[stevefivey]

Just to add to that I have found that the Primary side of the board has 250v, the secondary is dead.

 

[Nigel Goodwin]

Starting on a switch-mode PSU isn't a terribly good idea, they tend to be difficult to repair, and fairly dangerous as well.

Plasma PSU's are even worse, as they tend to be particularly obscure designs, and often are designed to be replaced rather than repaired - to that end, there are often no circuits or spares available.

 

[stevefivey]

cheers for the reply Nigel. Yes I appreciate what ur saying. I'm going to take a few capacitors out of the board and check them, also some of the diodes, just to see if its something that is easily fixable. Why cant you get spare boards for Samsung Plasmas? I keep getting directed to US sites. If anyone knows where I can get Samsung spare psu's in the uk, I'd love to know about it. I can forward part numbers etc. cheers

 

[Nigel Goodwin]

cheers for the reply Nigel. Yes I appreciate what ur saying. I'm going to take a few capacitors out of the board and check them, also some of the diodes, just to see if its something that is easily fixable. Why cant you get spare boards for Samsung Plasmas? I keep getting directed to US sites. If anyone knows where I can get Samsung spare psu's in the uk, I'd love to know about it. I can forward part numbers etc. cheers

Check with CHS, they sell Samsung spares - make sure you're sat down when you do though!.

 

[tvtech]

Starting on a switch-mode PSU isn't a terribly good idea, they tend to be difficult to repair, and fairly dangerous as well.

Nigel is correct. Rather start with something easier. Even Techs with many years experience battle sometimes to get a SMPS up and running without blowing up spares.....or getting shocked.

SMPS are unforgiving. These days, even a Variac does not really solve the problem when starting the SMPS after a total overhaul/repair job..
The SMPS started up @ around 90 Volts AC...picture the correct size, Line transistor collector voltage correct @ 120V and then it proceeded to destroy everything from the word go when I got to around 100 Volts AC. We run on 220 Volts AC here...

Major pissed off here. And the bloody main smoothing cap shocked me too. Twice.

And it is a simple Chinese SMPS circuit like all the rest we see....difference is this POS has it in for me.

Cheers

 

[tvtech]

Fixed it. Only the second or third time in thousands of TV's that I have seen a faulty Chopper TX. FFS.

They normally never fail.....or if they ever do not like this MF did. Man, this thing had me going crazy. Hope this helps someone out there.

You live and learn.

Cheers guys.