Apex ld3288m - No power, nothing

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Right, but that's where this is strange. If I leave the main board plugged into the power supply, as soon as I plug in the AC cord all voltages come on, though I get no outward signs of life (nothing on the panel, no power LED, etc). However, the 5 and 24 volts are both low (2.9v and 22.2v, respectively). Pressing the power button does nothing. If I unplug the three cables going to the main board, I get the expected 5VSB and 1.4v on the others (5V, 12V and 24V).

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

"Large cap never reads more than a few hundred mv" That large cap should have about 165~170VDC on it when the TV is plugged in, it cannot be in mV otherwise the 5VSTBY will not be working at all. Recheck your measurement, you have to measure it right at the two legs of the cap.

I was measuring the legs relative to chassis ground, should I measure relative to each other (probe on each leg)?

[budm]

Re: Apex ld3288m - No power, nothing

You are working in the primary side of the power supply, chassis ground is not the ground ref point for the primary side, that is why I requested to check the voltage right at the two legs of the cap in post 16, the negative leg of that cap the the ground ref point of the primary side circuit.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

390 volts across the cap.

[budm]

Re: Apex ld3288m - No power, nothing

OK, PFC is working, same for the STB signal is working otherwise the cap will not have 390VDC on it, also the power switch is working OK.
So we need to find out why the 5V is only putting out 2.9VDC.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

22.2v for 24v would seem low, as well. Those two go straight out to the main board. The fact that I don't have to power it on for these voltages to come up, and the power button goes to the main board, leads my gut to believe something wonky with the main board?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

This is the main board, to add to the pic of the power supply

http://assets.shopjimmy.com/media/ca...403a-top_1.jpg

[budm]

Re: Apex ld3288m - No power, nothing

So let me get this right, the 390VDC is on the cap the minute you plug the TV into the outlet, and the power ON/OFF switch does not do anything to make the voltage go back down to 170VDC? If that is the case, you then may have main board problem and also may be the low 5V problem as well.
One more test will be to disconnect that cable between the power supply and the main board so the STB signal will not be present, then see if the Voltage on the cap will still be at 390VDC.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

You're absolutely correct. And when I unplug the three cables between the power supply and the main board, the primary cap does go down to 170VDC.

[budm]

Re: Apex ld3288m - No power, nothing

OK, so the main board has PS_ON signal stuck on and causes the power supply to be activated, then the 5V power supply also has low voltage problem that can be due to bad power supply or the main board is loading it down too much.
You will have disconnect that 5V wire, then use 10 Ohms 5W resistor as the load for the 5V line to see if it will maintain 5V at @0.5A.
So you may have problem with two boards.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Great, thanks for the help. I'll have to run out for some 10 ohm resistors, I don't have any handy (nor anything less that I can put in series to get 10). I'll see if I can pop the 5V pins out of the connector and manually load it and see what happens.

And to be clear, I should route the 5V to ground via the 10 ohm resistor, correct?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Or just 10 ohm resistor to my meter (yeah, that makes a helluva lot more sense!)?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Quick question - what's readily available near me isn't 10 ohm 5w. I can get a 10w, would that be too much of a load?

[budm]

Re: Apex ld3288m - No power, nothing

Wattage of the resistor is how much power it can handle which is dictated by the voltage and current flowing through the resistance of the resistor. 10 Watts power handling is good. @10 Ohms and only 5V applied, it will only dissipate about 2.5Watts of power.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Awesome, thanks again!

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

4.92VDC without a load (released the two 5V pins from the connector). Headed out to grab the resistor I need, since I didn't have one in my parts drawer.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Good news, everyone! (/Farnsworth). The load from a 10 ohm resistor had absolutely no impact on the 5V output. Held steady with and without it. So looks like a failure in the main board. Is there any chance of troubleshooting that, or just a throw-away item?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I disconnected the cable coming from the side controls (power, volume, etc), to see if it was sending the on signal (if it was a faulty switch). No dice, same thing happens. So I see nothing else that it could be than the main board. So now it's a fork in the road - is the failure repairable, or just toss the board in the trash and get a new one?

[budm]

Re: Apex ld3288m - No power, nothing

Need to trace out that 5V line to see what it is feeding, may be then you can feel the components that may be getting warm/hot. If you put your meter in DC AMP mode than you can find out how much current is being drawn from that 5V line.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Will do, thanks!