Apex ld3288m - No power, nothing

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

5V traces run two different directions - one trace on the component side and one on the solder side. I can't differentiate which is which coming out from under the connector on the component side. On the solder side, it runs to a via to pop back onto the component side. It then runs into a SMD diode. It's the same strained 2.9v entering, but comes out at 2.2v. It then runs to a very small SMD cap with no voltage on the far side. The diode reads open in both directions, though that's in-circuit so probably isn't reliable. Nothing is running hot after 30 minutes. Or even warm.

[budm]

Re: Apex ld3288m - No power, nothing

I would do the current draw check using the meter, you will have to cut the wire and put the meter in series with the wire to check the current draw.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I'll do that next. No need to cut the wire, I was able to push the lock in to remove both 5V wires from the connector earlier, so I'll do that again.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Putting my meter in-line with one of the two 5V lines (there are two in the connector, but they are common - my assumption is they doubled-up for safety and/or current requirements) and leave the other disconnected, I get .47 amps. That should be roughly equal to the 10 ohm resistor test, which did not bring the 5V supply down.

[budm]

Re: Apex ld3288m - No power, nothing

"my assumption is they doubled-up for safety and/or current requirements" May be or may be not, should verify.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I did try both lines, one at a time, and got the same .47 amps. I cannot test both simultaneously as I only have one meter.

[budm]

Re: Apex ld3288m - No power, nothing

Since both wires are connected to the same 5V power source, you can tie the two wires together.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Strapping them together yields the same results @ .47 amps.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I also probed the temp of any sizable part - nothing above ambient room temp.

[budm]

Re: Apex ld3288m - No power, nothing

Boy, this is strange. Do you have any 5V wallwart switching power supply that you can use to power this 5V line?

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I can look, but it's doubtful. What about the 5V rail of a PC power supply? If that will work, how do I handle the ground?

[budm]

Re: Apex ld3288m - No power, nothing

That will work, just connect the DC output ground of the PC power supply to the chassis, then use 1A fuse for the 5V line. You probably should have dummy load connected to the PC PS, I do not know what the required min load is for your PC PS.

[tom66]

Re: Apex ld3288m - No power, nothing

When I test a PC PSU I always attach a 3.5" hard disk to one of the connectors, it provides sufficient minimum load. (Around 10 to 15 watts.)

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Actually, I forgot I have a 22" monitor with a blown inverter transformer and subsequently fried ccfls. The power supply, however, is solid. So I'll jump its 5V over to this set for testing.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

So here's what I found:

Ran the 5V of this TV off the 5V output of the 22" monitor's power supply. Current draw was a similar .53 amps. I had a solid 5V at the main board, versus the lower 2.9V of the original power supply. All other symptoms remain (390V across the primary cap, power button shows no sign of life).

So it's a head scratcher, for sure. On one hand, the main board did not bring down the 5V line of the other power supply. On the other hand, it still did not pull the primary cap down to 170V.

[tom66]

Re: Apex ld3288m - No power, nothing

It seems like the power board does have a problem, but it's right on the limit. Haha, what luck... The standby circuit also powers other parts of the power board, so a fault there can affect other parts. I would try replacing the startup capacitor.

[budm]

Re: Apex ld3288m - No power, nothing

Sure is a tough one, notes to self: cannot be 100% sure using dummy load testing power supply due the the logic circuits do not draw constant current.
Well I am not sure what else I can do, you do have main board problem and also power supply problem. From the way it looks, it has only one transformer where the 5VSTBY is generated, then it may have switched transistors for supplying switched 5V and 12V which are also generated by the same transformer.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

Ok, so here's an oddball question - that primary cap is 82uf @ 450v. I have a 140uf @ 400v, would it be possible to use that for a temporary test? I know the specs are out, but I've seen other references of people using other such variations without issue.

[tom66]

Re: Apex ld3288m - No power, nothing

A 450V minimum capacitor is recommended, because the ripple on the PFC can make the capacitor exceed 400V sometimes.

[DLinkOZ]

Re: Apex ld3288m - No power, nothing

I used that cap as a 30 second test, just to see what happens. Exact same scenario.