LG 52LG5010 ac detect sorted but still problematic

[satinser]

Continual cycling off and on. All voltages from power supply ok but PWR-ON voltage fluctuating between 3.3volts and Zero resulting in PSU ( EAY4175270) switching off and on.
After reading Tom66 excellent posts regarding this issue the AC Detect optocoupler was disabled (pc100). This corrected the non start issue. However I have another problem which may or may not be a consequence of this action. I have noticed a pinking noise from the PSU that appears to be related to the backlight level.
This noise is present all the time but not discernible on low backlight with back cover on. When Dynamic picture setting with 100% backlight it becomes more noticeable even with back cover on. However I cant be sure that this isn't a totally different issue because the TV came in as a non starter. Any thoughts on this would be appreciated.

[tom66]

Re: LG 52LG5010 ac detect sorted but still problematic

"Pinking noise" ?
Please describe further. Never head of this before.

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Its difficult to describe but think its associated to backlights. Tried disconnecting the both inverters used in this model. The backlight obviously dont then work but the noise is then no longer apparent. I likened it to pinking because it sound some thing like a car engine out of tune when the old carburetor was present before electronic ignition.

[tom66]

Re: LG 52LG5010 ac detect sorted but still problematic

I really have no idea what you mean, I have never worked on a car aside from helping with jump starting my dad's car.

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Its difficult I know Ive never heard anything quite like it before you could liken it to a metalic chirping like noise. Only when backlight is set to a high level.

[tom66]

Re: LG 52LG5010 ac detect sorted but still problematic

On some power supplies that -can- be normal.
You'd really have to scope the output to be sure...

[cliff_hootarski]

Re: LG 52LG5010 ac detect sorted but still problematic

Are you trying to say "pinging"?

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Its difficult I know Ive never heard anything quite like it before you could liken it to a metalic chirping like noise. Only when backlight is set to a high level.

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Its too obvious to be normal. I dont think its anything to do with the ac detect repair issue as just spoken to owner of TV and he said that he had noticed it before and by turning the backlight level down found that it had stopped.
Still like to know whats causing though.

[tom66]

Re: LG 52LG5010 ac detect sorted but still problematic

Well, do you have access to an o'scope?

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Afraid not. Now found that applying a bit of pressure to the heat sink that's got the bridge rectifier attached too it stops the noise. Will in all probability find that there's a dry joint somewhere around that area that's the cause of the issue.

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Checked for dry joints but afraid none found. The metallic chirping increasing if back light turned higher. Tried disconnecting both master and slave inverter and in sound only mode the chirping stops. So wondering whether its a fault in the back light that's causing the chirp in the PSU and not the PSU itself. Applying slight downward pressure to the Bridge Rectifier heat sink definitely decreases the chirping sound. Is there a possibility that the bridge rectifier itself could be causing this noise with some type of internal short?

[ron77]

Re: LG 52LG5010 ac detect sorted but still problematic

Recently repaired one of these TV's. The fault was relay clicking on and off continuously. With back on relay clicks. Take back off, set worked perfectly if room lit. Ordinary daylight enough to keep tv running. Take back off at night, in dark room, tv would keep on clicking. Putting insulation tape over zd102 kept relay clicking. Replacing zd102 16v zener cleared fault. Also replaced zd503 because it read 15v, instead of 16v. Zd102 did not read faulty, and replaced with same type, In5246b. The tv on test all this week and is working fine.

[satinser]

Re: LG 52LG5010 ac detect sorted but still problematic

Just like to point out that I have today repaired an LG power board with AC detect fault again by bridging pins 3 and 4 of optocouplers ic101 and ic102.
Power supply used on LG 50PG3000
EAX38865401/7 EAY39190301.

Fault was not continual clicking but switch on and straight off to standby with red standby illumination tuning to blue and returning to red after a few seconds.
Adding this information in case it helps referring to this thread in the future.

[nomoresonys]

Re: LG 52LG5010 ac detect sorted but still problematic

Just like to point out that I have today repaired an LG power board with AC detect fault again by bridging pins 3 and 4 of optocouplers ic101 and ic102.
Power supply used on LG 50PG3000
EAX38865401/7 EAY39190301.

Fault was not continual clicking but switch on and straight off to standby with red standby illumination tuning to blue and returning to red after a few seconds.
Adding this information in case it helps referring to this thread in the future.

If I understood it right, the optos are faulty? Wonder if there's any downside to fixing it like that? would the optos wear out faster maybe?

[R_J]

Re: LG 52LG5010 ac detect sorted but still problematic

The fault is in the circuit that drives the optocouplers, Whatever the fault is, this is just bypassing the fault detection circuit.
IC101 is part of pfc circuit, There could be a problem with the pfc circuit thats causing the other problems, The pfc voltage is likely too low, when the tv (backlights) demand more current, the power supply can't supply it, causing the noise you here. What is the voltage across the main filter? I suspect the pfc circuit is not even running and the rest of the power supply is operating from the 340v dc


Pink noise is similar to white noise

[nomoresonys]

Re: LG 52LG5010 ac detect sorted but still problematic

Ok I see, thanks.