LG 50PQ6000 unstable 5v standby

[tom66]

Re: LG 50PQ6000 unstable 5v standby

That is fine, the PFC is switching off.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Wow something works!

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

so why does it go nuts when I plug in the Y-sus and Z-sus boards?

[tom66]

Re: LG 50PQ6000 unstable 5v standby

Perhaps the low 3.5V is causing problems with the rest of the logic.

[ben7]

Re: LG 50PQ6000 unstable 5v standby

That is fine, the PFC is switching off.

I don't think it is fine for it to be jumping all over the place when its in the TV, right?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Another area I have a question mark over:

ACDETECT with the board dissconnected from the TV jumps about with the clicking but never over 1v?

maybe a clue to you guys?

When I connect the board to the TV it gets the 3.5VDC somehow.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

I don't think it is fine for it to be jumping all over the place when its in the TV, right?

I would expect it to be stable when working.

[ben7]

Re: LG 50PQ6000 unstable 5v standby

I would expect it to be stable when working.

Me too.

What does the manual say about the ACDETECT? I.E., does it say that when AC is detected, the ACDETECT pin is high? low? what about if there is a power failure (AC power drops out, due to power outage, or being unplugged)?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

AC Detect is generated on the SMPS, by rectifying a small sample of the
A/C Line at D102 and associated circuitry and routed to the Controller (IC701) where it outputs at pin 15 and sent to P813
pin 18 to the Main Board where it is sensed and monitored by the Main Microprocessor (IC1). The AC Detin this set works differently than most. If AC Det is missing the Microprocessor will turn off the television in about 10 seconds after turn on.
This will happen each time turn on is attempted.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

PIN:18
LABEL:AC Det
STBY:5V
RUN:5V
DIODE MODE:Open

[ben7]

Re: LG 50PQ6000 unstable 5v standby

AC Detect is generated on the SMPS, by rectifying a small sample of the
A/C Line at D102 and associated circuitry and routed to the Controller (IC701) where it outputs at pin 15 and sent to P813
pin 18 to the Main Board where it is sensed and monitored by the Main Microprocessor (IC1). The AC Detin this set works differently than most. If AC Det is missing the Microprocessor will turn off the television in about 10 seconds after turn on.
This will happen each time turn on is attempted.

That would mean that when there is AC, the ACDETECT would be high, as it is when the mainboard is connected in your case.

I don't know why it would be low with no mainboard, but I think some of the filter caps next to the small heatsink on the bottom right could be dried up inside.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

ok the 3 capasitors? I will remove and test tomorrow. It looks like there is another rectifier, an IC and another thing with 3 legs fitted to the heat sink.

So it this like another 5v supply circuit and those capasitors are filtering out noise?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Manual said its the STBY 5V, 5V, 12V Source

[ben7]

Re: LG 50PQ6000 unstable 5v standby

Manual said its the STBY 5V, 5V, 12V Source

They are saying that the 5v standby is derived from 12v [standby]?

I think there could definitely be an issue with the capacitors.

Can you take a close up of that side of the board? So we can see the ICs/rectifiers part numbers?

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

They are saying that the 5v standby is derived from 12v [standby]?

I think there could definitely be an issue with the capacitors.

Can you take a close up of that side of the board? So we can see the ICs/rectifiers part numbers?

Hope these are good enough.

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Do you need the back also?

[ben7]

Re: LG 50PQ6000 unstable 5v standby

Do you need the back also?

Sure, wouldn't hurt!

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

MANUAL:

AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input assembly. Standby 5V is developed from
160V source supply (which during run measures 380V measured fromthe primary fuse F302).
This supply is also used to generate all other voltages on the SMPS.
The STBY5V (standby) is B+ for the Controller (IC701) on the SMPS and output at P813 pins 11 and 23 then sent to the
Main board for Microprocessor (IC1) operation.

[tom66]

Re: LG 50PQ6000 unstable 5v standby

If possible. I suspect the 5V MAIN is derived off here...

If the 12V is also low by about the same amount (30%), then the suspect would be the primary side, controller IC, or TL431.

I say TL431 because I now recall budm had a Samsung monitor with low rails, and it turned out to be the TL431 (voltage reference IC; for the feedback loop.)

[Baileybum1234]

Re: LG 50PQ6000 unstable 5v standby

Rear of low voltage board area.