LG 60LB5200 No power , completely dead

[Anooc7]

Re: LG 60LB5200 No power , completely dead

I jumped r33 but still issues remains the same. Before ordering a psb this was the only experiment remaining, I doubt the purchased IC’s quality at this moment, but not taking chances anymore.
Thanks all for your time.

[Davi.p]

Re: LG 60LB5200 No power , completely dead

If the output tensions were lower on standby this should be indicated in the silkscreen table. Usually when low outputs are present i suggest to change the feedback optocoupler and the shunt reference, that here are U3,U6, because the spike when mosfet is off runs through the IC and after that trespasses the opto and hits the shunt regulator, but this has nothing to do with the r33 burning i think..

[R_J]

Re: LG 60LB5200 No power , completely dead

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[Anooc7]

Re: LG 60LB5200 No power , completely dead

If the output tensions were lower on standby this should be indicated in the silkscreen table. Usually when low outputs are present i suggest to change the feedback optocoupler and the shunt reference, that here are U3,U6, because the spike when mosfet is off runs through the IC and after that trespasses the opto and hits the shunt regulator, but this has nothing to do with the r33 burning i think..

That is a good input , but
I have already closed the unit and decided to order a replacement psb, when it comes I will do a side to side analysis and will post the findings.
Regards

[Unspun01]

Re: LG 60LB5200 No power , completely dead

That is a good input , but
I have already closed the unit and decided to order a replacement psb, when it comes I will do a side to side analysis and will post the findings.
Regards

Hi:

I also have same TV 60LB5200. My power supply had low 12V and 24V. They measured 8V and 16V respectively.

I replaced the main IC TEA1755T, but there was no difference. Low 12V and low 24V is not due to the main IC.

The solution is simple. Replace surface mount NPN transistor marking 2X at position Q13. 2X marking is a MMBT4401 NPN BJT transistor 40V 600mA.

This transistor was not shorted in my power supply and i thought it was ok and overlooked it. But nearby resistances did not measure correctly in circuit.

Measure resistance of highlighted components in-circuit: R79 [102] = 1kohm, R84 [102] =1kohm, R87 [222] =2.2kohm. If in-circuit resistance of any of these do not appear to match their stated value, remove Q13 and re-measure the resistances.

In my TV, the in-circuit resistances were way off. With Q13 removed, these resistances matched their stated values exactly. When I replaced Q13, the power supply correctly output 12V and 24V once again.

None of the resistances needed to be replaced or removed. I only highlight them to assist anyone in determining if Q13 is bad.

This does not preclude the other nearby transistor (Q12) or 431A IC (U3) from being bad, but they were not the issue in my TV.

Please try my tests, and my solution and reply with your findings.