Samsung LCD won't power on help!
 

Last week I got three LCD TV freebies off of craigslist, one being this Samsung LN32C540F2D 32" set that will not power up. It was built in Aug 2010 and already dead!

As usual I looked for blown caps, none were puffy looking but I replaced all of them on the power supply board anyway. Still does not power on. The red standby indicator is on and no other response.

Any Ideas?

Thanks in advance!

Measure the power supply output voltages. See if the circuitry is receiving power. If the standby light is on, there is standby power. So the problem may be in the circuitry that triggers the main power supply.

You will need a schematic diagram and some test equipment to solve this one.

I have had newer sets with bad mainboards. If it is a common issue, the boards wont be available or all sold out. I had to part out a few newer sets just because parts were NLA. If the PS is labeled, you can jump the 5V(or 3.3V) and pwr on pins and see if it does something

Did you try a remote? Sometimes those touch-sensitive buttons stop working (if yours has those, most samsungs of that era do).

I was thinking if you try a remote for ANYTHING, and see if that standby light flashes. Both my Samsung sets the light flashes anytime it sees remote activity from ANY of the IR remotes.

It may only do that when it's on though. I've not paid attention to if I see that flashing with the set not on.

The only voltage I see is 5v on one pin marked A5V, all others are close to 0.

The board is labeled. I did jump 5v to the PS-ON and no response.

I did try a different remote, no change. The original remote seems to work when viewed through a digital camera.

My next plan is to test the PS board, I just need to find my isolation transformer. Anyone know where to find a schematic?

The PS-ON terminal is not an input; it's a signal that the power supply is on. If you don't have that, then the power supply needs to be triggered.

Most of those power supplies use a bridge rectifier off the power line that goes to a switching circuit, a MOSFET on a heat sink with an IC controller and a flyback diode and an inductor to generate a signal to go to the little high frequency power transformer.

So first see if you are getting AC to the bridge, DC out to the MOSFET. You probably do, and thus the problem is in the control circuitry that tells the IC to start up.

Any more detail probably requires a diagram. One thing you can do, with power off and all capacitors discharged, measure every diode, resistor, and transistor to see if any are open or shorted. Also check for fusible resistors; they are usually gray or light blue dull finish, about a 1 Watt size or smaller. If one has opened, there is the problem. Of course, there may be an important reason it has opened.

The PS-on has to be triggered by the main board. usually 5V or 3.3, just depends on the TV. I repair TV's most every day. That is how I test power supplies when they are not in the TV. Jump the 5V to the PS-ON terminal to trigger the PS to turn on. Then I test voltages to make sure it's working correctly. That's how every TV guy I know does it. I suggest looking at the Coppell TV repairs web site. look at the blog section on the repairs that he has done. he also shows how to test the PS in the way I describe. This method works for me.

I stand corrected. I am coming from a different perspective, as I don't work on TV.

Today I pulled the PS board and noticed a loose part hanging underneath. It appears to be a SMD Zener diode that is very tiny and is marked "H2". I don't know if it's blown out or just broken off, it was hanging by one lead. The board is marked DZB802. It looks like it is located in the primary side.

The H2 marking is confusing, some datasheets say it's 12v, some say different.

If the other lead is still attached to the diode, try to resolder it. You can always tack a standard sized zener in there for testing purposes. 12v or higher should be OK.

I tacked in another Zener and still no response. Also tried jumping the PS-ON to 5v and tried jumping it to ground, no change.

I'm going to set it aside for now and look for a similar TV with a broken screen and make one out of the two.

Thanks for your help!