BN44-00424A Continuous Restart

[mmartell]

This is from a 55" Samsung LED tv. I have no idea of the expected behaviour but seems faulty to me. The set doesn't work with the mainboard plugged in so I unplugged it to try and isolate fault.

When plugged in by itself (or with led) there is a faint tick that sends all voltages rising momentarily, then back to zero and over again. Cycle takes 4-5 seconds. The 5VSB line is the only line rock steady.

What confuses me is the three pins generated by the mainboard (PSON, BLON and DIM) rise and fall in voltage as well (without mainboard attached!). So it seems like a short is causing stray voltage and tripping whatever protection the board has.

How can I determine if the PS is faulty and which component is causing the problem ?

[mmartell]

Re: BN44-00424A Continuous Restart

Some pics...

[mmartell]

Re: BN44-00424A Continuous Restart

Ok then... let me ask this.

Is there a way to separate the Primary from the Secondary to see if it keeps rebooting so I know which half the problem lies in ? And is it possible to keep the Standby voltage active when disconnecting the Secondary ?

[cheapie]

Re: BN44-00424A Continuous Restart

Sounds like it's going into protection. See if any of the outputs are shorted.

[mmartell]

Re: BN44-00424A Continuous Restart

Can I do that by measuring the connectors pins to see if any are shorted to ground or should I measure that somewhere else ? Detailed help is appreciated this is my first real time at this.

[cheapie]

Re: BN44-00424A Continuous Restart

Can I do that by measuring the connectors pins to see if any are shorted to ground

Yes.

[mmartell]

Re: BN44-00424A Continuous Restart

18v - 650ohm
13v - 475ohm
5v - 167ohm

5VS - ohms keep increasing like it's charging a capacitor

The other pins (PSON, EPWM and BLON) measure in the k-ohms

[senz_90]

Re: BN44-00424A Continuous Restart

Ok then... let me ask this.

Is there a way to separate the Primary from the Secondary to see if it keeps rebooting so I know which half the problem lies in ? And is it possible to keep the Standby voltage active when disconnecting the Secondary ?

you can try jestine book about smps method to isolate the problem is on primary or secondary side. for note, im not salesman of any kind manufactures or site, but i think his method is good to separating problem in smps.
btw are measuring this connector pins to ground both ways of probes? if you get same resistance reading both ways then maybe the problem is on secondary side.

[mmartell]

Re: BN44-00424A Continuous Restart

Oops no I did not - one direction only. Will follow up on that.

[mmartell]

Re: BN44-00424A Continuous Restart

Pulling PSON low stops the cycling and still provides 5vsb. Pulling it high (5vsb or 3.3v) brings back same behaviour.

[momaka]

Re: BN44-00424A Continuous Restart

This is from a 55" Samsung LED tv. I have no idea of the expected behaviour but seems faulty to me. The set doesn't work with the mainboard plugged in so I unplugged it to try and isolate fault.

See if the PSU still ticks and if the voltage still go up and down when the PSU is connected to the TV when you try to turn it on. Some PSUs do not like to run without a load and will shut down like that. If there a label somewhere on the board that says how much current each output is rated for, you can try to add some resistors and 12V car bulbs to the outputs rather than have the PSU connected to the TV to see if it still does the same thing.

I also see that there are lots of SamWha or SamYoung capacitors on the board. Definitely change the very small ones on the primary side first (i.e. any "startup" caps). So CM802, CP812, CM812... etc. - those tiny ones.

Also, check all large "power" diodes and rectifiers on the secondary side.

Pulling PSON low stops the cycling and still provides 5vsb. Pulling it high (5vsb or 3.3v) brings back same behaviour.

That seems normal. Most TV PSU (unlike computer PSUs) need to have PS_ON pulled high to tun ON and pulled low to turn OFF.

[mmartell]

Re: BN44-00424A Continuous Restart

The load thing is a possibility. I can't use the mainboard for anything it's very nearly dead. When connected it seems to leave pson floating.

[mmartell]

Re: BN44-00424A Continuous Restart

Ordered a main board for the set this PS belongs to to rule out that possibility.

[mmartell]

Re: BN44-00424A Continuous Restart

Replacement main board didn't solve the issue.

I will merge this with the thread about the Samsung tv this supply is from. See here.

Post #45 is where we are but feel free to scroll through the rest to get some history on it.

[senz_90]

Re: BN44-00424A Continuous Restart

Replacement main board didn't solve the issue.

I will merge this with the thread about the Samsung tv this supply is from. See here.

Post #45 is where we are but feel free to scroll through the rest to get some history on it.

so did power supply or mainboard were failed?

[mmartell]

Re: BN44-00424A Continuous Restart

Looks like both. Trying to figure out now why the PS won't ramp up the secondary voltages without restarting.

[senz_90]

Re: BN44-00424A Continuous Restart

good luck. i hope if i could help you.

[mmartell]

Re: BN44-00424A Continuous Restart

I need an SMPS for Dummies primer to do any effective troubleshooting. Too many large gaps in my knowledge.

[senz_90]

Re: BN44-00424A Continuous Restart

i dont know if this help. but try to remove the transformer of smps and see that is still restarting or remove secondary diode one by one except the feedback ones after attach again this transformer to circuit to determine where section is failed. but try to hear others advice because i just know how to troubleshoot a smps at beginner level.

[mmartell]

Re: BN44-00424A Continuous Restart

Problem is I can't tell a secondary output diode from a feedback diode so if somebody wants to point them out I will gladly try that.