LGP32-09P Power Supply Problem. Not getting 24V and 12V

[retrorepair]

Hi all,

I´ve been mostly a reader of this forum, and it rocks! But now i need help from you guys.

The TV arrived with only standby led lightning. I have found IC100 (L6599DTR) to be defective on the 24V and 12V power supply. Changed IC100. After changing IC100 i've got the following situation:

- Power supply has 5V Standby.
- TV sends signal to turn 24V and 12V on.
- Q501 turns on VCC.
- VCC is 14.8V.
- 12V reads 5.3V and 24V oscillates between.
- PFC is working (389V on C608).

What i've done so far:

- Measure capacitors on the output: OK!
- Measure shorts on 24V and 12V to ground: No shorts!
- Check feedback circuit on secondary side: No problems found.
- Changed Optocoupler even if the original was ok: No changes.
- Checked C112: Ok.
- Checked C113 on the ISEN line of IC100: Ok.
- Checked all resistors (throughole and snd): All ok.

Finally i swapped the power supply with a known good one and the tv works great, but that is from other tv that i cannot spare.

Can you guys give me some clues? Do i have to swap the ceramic smd caps that are surronding IC100, namely C117 who is responsible for the oscillator frequency? I suspect that because the transformer of the 24V and 12V is making a whinning noise...

For the records, if i put a load of 500 ohms on the 24V, the voltade drops 2V!!!

Thanks in advance.

Sorry for my poor English.

Greetings,
Retrorepair

P.S: already checked the diodes around IC100 and MOSFET's.

[nomoresonys]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Check the diodes.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Check the diodes.

Hi nomoresonys,

Thanks for you reply. I forgot to mention that i already checked the diodes(D104, D105, ZD101, D102 and D103 going to MOSFET's). All fine.

[dick_barton]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Do you have the power supply schematic?

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Do you have the power supply schematic?

Hi dick barton,

Thanks for the reply. Yes i have.

[R_J]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Where did you measure the VCC voltage? Try replacing C507 and C508, (don't just check them), your vcc could be too low, Q501 acts like a switch/regulator, the voltage is set by the 16v zener diode in the base, The collector should be around 25v~28v, the emitter will be about 16.5v

You did'nt say if you checked D251,D252 & D254

[nomoresonys]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Maybe heat up those caps in that area with a hairdryer, see if tv works and or the whine goes away or lessens if only for a while, just a little test to try.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Where did you measure the VCC voltage? Try replacing C507 and C508, (don't just check them), your vcc could be too low, Q501 acts like a switch/regulator, the voltage is set by the 16v zener diode in the base, The collector should be around 25v~28v, the emitter will be about 16.5v

You did'nt say if you checked D251,D252 & D254

I've measure de VCC voltage on Emitter of Q501. Yes it acts like a switch. On the collector i'm getting around 16V more or less. I guess IC500(ICE3B0365J) is not working correctly, as i only get 12.9 volts on pin 7, and that voltage come from the same winding of T501 who is responsible for getting the correct voltage to the collector of Q501.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Maybe heat up those caps in that area with a hairdryer, see if tv works and or the whine goes away or lessens if only for a while, just a little test to try.

Already did that with no changes.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Hi all,

Just a quick update.

Chenged all electrolitic caps, same behaviour.

Chenged all zener diodes, same behaviour.

I'll try to change IC500 who is responsible for generation VCC, because this voltage is a little low. If you have other clues for me, go ahead.

As soon as i replace IC500, i'll get to you.

Best regards,
Retrorepair

[budm]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Post #1: PFC is working (389V on C608).
I doubt that Standby IC 500 will solve based on you r report that the PFC is working OK, the PFC IC gets the same VCC to run from Q501. Beside, the 5V STBY output is steady, correct? if the IC is bad the 5V output will be bad also. BTW, what Voltage do you have on VCC pin of the PFC IC?
Can we see good clear straight shots of the whole top and bottom side of the board? Did you check DC BLOCKER/COUPLING Cap C112?

Look at spec sheets of the IC's:

IC500 ICE3B0365
https://cdn.badcaps-static.com/pdfs/...6c177f8dcd.pdf

L6562A PFC IC: VCC turn on threshold is 12.5V, turn off threshold is 10V.
https://cdn.badcaps-static.com/pdfs/...39949d5f59.pdf

L6599 SMPS: VCC turn on threshold is 10.7V, turn off threshold is 8.15V
https://cdn.badcaps-static.com/pdfs/...7b0cc85afc.pdf

[R_J]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

You say you replaced all the zener diodes, I will assume ZD501 also, Did you check R503 (1.2Ω)? The other thing I might try is the optocoupler, if you don't have one, exchange ic501 with ic502.
What is the voltage on C507 with the tv in standby? is it still low?

[nomoresonys]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Luckily you have a good board to check the bad one with, maybe compare all those key voltages, see if any are different, did you check all the mosfets? could it be one of the non-electro caps? you did hit all the caps with the hairdryer? checked all solder joints with a magnifying glass?

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Post #1: PFC is working (389V on C608).
I doubt that Standby IC 500 will solve based on you r report that the PFC is working OK, the PFC IC gets the same VCC to run from Q501. Beside, the 5V STBY output is steady, correct? if the IC is bad the 5V output will be bad also. BTW, what Voltage do you have on VCC pin of the PFC IC?
Can we see good clear straight shots of the whole top and bottom side of the board? Did you check DC BLOCKER/COUPLING Cap C112?

Look at spec sheets of the IC's:

IC500 ICE3B0365
https://cdn.badcaps-static.com/pdfs/...6c177f8dcd.pdf

L6562A PFC IC: VCC turn on threshold is 12.5V, turn off threshold is 10V.
https://cdn.badcaps-static.com/pdfs/...39949d5f59.pdf

L6599 SMPS: VCC turn on threshold is 10.7V, turn off threshold is 8.15V
https://cdn.badcaps-static.com/pdfs/...7b0cc85afc.pdf

Hi,

Sorry for the delay, but have benn doing other equipments for costumers.

The standby voltage is stable 5.1V.
PFC VCC pin is 14V.Blocker/coupling cap C112 is bang on 47nF.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

You say you replaced all the zener diodes, I will assume ZD501 also, Did you check R503 (1.2Ω)? The other thing I might try is the optocoupler, if you don't have one, exchange ic501 with ic502.
What is the voltage on C507 with the tv in standby? is it still low?

Yes, tried everything. Standby voltage is Ok 5.1V steady.

14.8V on C507. No problem there.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Luckily you have a good board to check the bad one with, maybe compare all those key voltages, see if any are different, did you check all the mosfets? could it be one of the non-electro caps? you did hit all the caps with the hairdryer? checked all solder joints with a magnifying glass?

Hi,

Unfortunately i had to deliver the other board(TV) repaired to the costumer. I don't have it now.

[retrorepair]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Hi all,

Thanks for all the help that you gave me. This forum rocks.

I beginning to think that T101 is somehow bad.

The PSU works with all the voltages if i turn it on with a 1k resistor from 5V to PSON. If i do that, i get 5.1V standby, 24.06V on the 24V output and 12.1V on the 12V output. But i get this weird whinning on T101. In this circumstances if i put a load of 500 ohms on 12V, it drops to 11.2V and the 24V output rises to 25.6V. If i put a load of 500 ohms on the 24V, it stays ok but the 12V output rises.

Let see some facts:

- with no load, all outputs are ok.
- with load on 12V output: 12V drops to 11.2V and 24V rises to 25.6V.
- with load on 24V output: 24V stays ok but 12V output rises.

I already checked the feedback circuit on this part of the power supply, all components tested ok. Changed optocoupler IC101, same behaviour. Changed IC251 (AZ431), same behaviour. All resistors and caps are ok (measured and tested outside the power supply).

I'm out of ideas. T101 is the last component that i didn't change. All i have done was take T101 and measured the windings to check continuity. I don't have a meter to test T101 indutance.

Best regards,
Retrorepair.

[dick_barton]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

500 ohm load on the 12V supply delivers a load current of 24mA however on the board it says the 12V can supply 2Amps.
I would look at checking the diodes D255, D256 for leakage and also replace C253.
Transformer noise is sometime created due to the failing, but not completly failed, rectifying diodes.

[dick_barton]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Also check C120 and D104 which provide feedback to the L6559 of the load current drawn by the secondary supplies.

[dick_barton]

Re: LGP32-09P Power Supply Problem. Not getting 24V and 12V

Where are you based?

If you replaced IC100 I would double check all the solder connections just in case.

C120 and D104 are smd devices to be found underneath the board close to IC100.