Samsung LCD LN32C450 Power Problem

[tech2014]

I got a tv that when powered up, it stays on for a few seconds and then the power LED goes off and stays off. I found that when I removed the connector going from the power supply to the inverter board, the power would stay on and the power LED would stay a solid red, but tv would still not power up. I assumed it was a bad inverter board, so I replaced it. I put the new board in and same problem. The power supply is BN44-00338B.

I was able to test the power supply. With the p/s out side of the tv, I was able to get voltages WITHOUT putting 5v on the PS_ON pin. I get the following voltages

5.3v=ok
5v=ok
13V=16.5V
24V=31V

I googled this power supply and apparently there are issues with a SIC cap CM808 and ICM801. I removed the cap CM808, which is 18nf. I measured it out of circuit and it measures 2nf.

Would this cap having too low capacitance cause the voltages to be higher then normal or am I missing something here. thanks

Below is a pic of the power supply, back of the TV and the power supply schematic. Any help would be greatly appreciated.

[budm]

Re: Samsung LCD LN32C450 Power Problem

First, you need to check the battery of your meter, your readings are way high so more likely the battery is low.
Low capacitance will cause the 12V/24V DC to be low.

[paulstef]

Re: Samsung LCD LN32C450 Power Problem

2nF instead of 18nF is definitely not good in a resonant power supply. It needs to be replaced.

If you test the PSU disconnected from the rest the voltages are probably higher though because they are not loaded.

[tech2014]

Re: Samsung LCD LN32C450 Power Problem

BUDM, I did replace battery a couple weeks ago so its not the battery.

[tech2014]

Re: Samsung LCD LN32C450 Power Problem

I get PFC voltage of about 390V going into CM808, which measures 2nf out of circuit, so I am going to order a new part. Should I replace ICM801 as well?

[budm]

Re: Samsung LCD LN32C450 Power Problem

That cap is the coupling cap to drive the power transformer, when the capacitance is low the output Voltage will be really low with only 2nF, so yes replace cap first since it is the commonly failed cap.

[tech2014]

Re: Samsung LCD LN32C450 Power Problem

thanks guys

[johns1mj]

Re: Samsung LCD LN32C450 Power Problem

I have the same problem and found a repair kit on ebay for $15. I am going to try it. While in I have all my powers and grounds according to the chart posted on the power board. Unhooking the t-con and led driver did not produce any changes.

[johns1mj]

Re: Samsung LCD LN32C450 Power Problem

I now have back lighting if I unhook the input board but no joy on the start up chine. No back lights if I leave the input board hooked up. I also get no response on the touch buttons.

[ReeceyBurger123]

Re: Samsung LCD LN32C450 Power Problem

Mainboard is faulty then.