Apex ld3288m - No power, nothing

[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

"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)?

[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).

[budm]

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.

[budm]

Re: Apex ld3288m - No power, nothing

The 5VSTBY is the always on power supply, it will be present when the the TV get the 120VAC to it, it is used for running the micro controller on the main board. When the power switch or Remote power on is activated, the main board will send the PS_ON to turn on the rest of the power supply section.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Large cap never reads more than a few hundred mv, simply a few hundred mv negative on the negative lead. Like I said, it doesn't respond to the power button, so I have no idea what it would do in an ON state. At this point, I'm trying to determine if it's the power supply not putting out enough voltage (see the 12 and 24 volt readings above) or the main board dragging them down. I think those would be my only two scenarios, due to the simplistic nature of this TV.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

That's the oddity, it won't turn on. The 5VSTB always has 5v, regardless of connectivity to the main board. However, when I connect the main board I get voltages (though some are out of tolerance). Hitting the power button does nothing. I'll check the voltages and report back.

[budm]

Re: Apex ld3288m - No power, nothing

That STB may be active LO, if that is the case, check the DC voltage at STB pin when TV is OFF and when TV is turn on. Also check the DC voltage on the two legs of that large 450VDC filter cap when TV is OFF and when it is ON.
The 5V low but the 12v is OK, then I would look further in the 5V rectification and filter section, or it may be loading down by the main board.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I put a 1k resistor between the first two pins on the far left in the picture above (labeled STB and 5VSB) and there was no difference - 5V, 12V and 24V all stayed at 1.47v. But they do go up if I connect the main board (at 5v - 2.9v, 12v - 12.2v, 24v - 22.2v). Here is the full power supply.

[budm]

Re: Apex ld3288m - No power, nothing

You can force on the power supply board by itself by using 1K resistor between STB (PS_ON) pin and the 5VSTBY, the connector has to be removed so it will be pulling down the STB pin.
Can we see the picture of the whole board? We need to find out if it has PFC Voltage booster circuit or not.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

So after some time away from it, I decided to take another quick peak at this thing. Something that strikes me as odd:

Without the main board connected, I get 1.4v on the 5v, 12v and 24v. 5vsb is fine, which I would assume is proper. If I connect the main board, I get the previously-mentioned out-of-spec voltages. But I shouldn't at this point, right? I haven't hit the power button, or otherwise turned it on however the main board *seems* to be invoking a power-up of the power supply. Or could this be simply due to the super-simple design of the TV (two boards main and power, power also has inverter hardware) and its components?

The power supply has only 6 connectors - input mains from outlet, 2x output to the backlighting, and the three connectors pictured that go to the main board. My question, so I can see if the power supply is simply not outputting proper voltage or if the main board is dragging it down, is can I force the power supply to power on without the main board connected? That way I can read power output without any load.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I may just grab a replacement main board, they're very cheap. Does anyone know if there's anything that differentiates those for a Westinghouse from one for an Apex? Same part number for the board, but want to make sure there isn't something strange that's done per-manufacturer.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

The main board, CV318H-X, seems to be widely-used on Westinghouse and ProScan sets. Just trying to get as much potentially useful info as possible.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I recapped two TVs' power supplies today - another was an LG and it's back up and running. This one, however, no change. 5vsb and 12v still look good, 5v and 24v are still low. I don't have the original remote, but programmed the only code that my DVR's remote says works for Apex Digital LCD sets (just in case the power button is faulty) and still no-go.

Any input as to further testing? The idea of excessive load bringing down those rails seems like it may be on the right track, as I mentioned earlier sometimes when I plug it in it causes a quick flicker of the lamps on that same circuit.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Without the main board, I believe I was getting *only* the 5vsb. The power button routes through the main board and then triggers the power supply. I did trace the 5v (that reads 2.9v) back to a cap that seems suspect using the old unreliable test method (continuity one way to see resistance go up, then swap leads and watch resistance go down then back up again, it's OL one direction and works the other). I know, not a good test but definitely doesn't look right and there are a few caps that act like that. I cataloged all the caps last night and will replace them all, just in case.

[tom66]

Re: Apex ld3288m - No power, nothing

You may have bad capacitors on the 5V and 24V lines, or excessive load on those.

[notallbad]

Re: Apex ld3288m - No power, nothing

try taking the readings with the power supply disconnected from main board, is the 5v still reading 2.9v?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Clarification - 5vsb is 5.2v, 5v is 2.9v

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Checking the power supply output:

1st 5v - 5.2v
2nd 5v - 2.9v
12v - 12.2v
24v - 22.2v

One of the 5v is nearly half down, and the 24v is quite low. I'm going to pull the board back out, and see if I can follow the traces back to see what differentiates the two 5v outputs.

[tom66]

Re: Apex ld3288m - No power, nothing

A good start is to check power supply output voltages: if they are bad, further troubleshooting can be done, but otherwise it may be a main board (=main unit) fault.