LG PSU EAY40504401 (LGP32-08H) repair

[Chungalin]

I've seen this board incorrectly refered as EAY4050440, because last digit is a dot in a matrix (see right-bottom corner in attached image). I've always seen "1" marked, so real LG part for 32" is EAY40504401 (LGP32-08H).

For 37" it's EAY40505001 (LGP37-08H), sharing the same PCB, only primary mosfets change.

It can be found in LG 32LG3000-ZA model, among others.

I've found schematic too.

I haven't seen any of these fail of secondary capacitors. They have more subtle failures in primary side.

One common failure is at SMD resistors in series R609, R610, R611, R612 (620kΩ x4 = 2,48MΩ ≈ 1MΩ + 1MΩ + 470kΩ). This affects PFC.

I've one that after some minutes (cold start) it drops AC Detect signal ("ACD") but keeps generating 5V Standby. Haven't found solution to this one yet.

[ReeceyBurger123]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Ive done this where the controller for the 24v rail fets fails as well.

[budm]

Re: LG PSU EAY40504401 (LGP32-08H) repair

If the incoming AC is within the operating range.
check the OPTO PC501 Voltages on both side of the OPTO (make sure to use correct GND ref for each side of the circuit) when the TV is working and not working. Also try cooling and heating the opto. There are also many high Ohm resistors in the ACD detection circuit that you need to check the value, if the resistance goes up it will cause ACD problem.

[jknotts]

Re: LG PSU EAY40504401 (LGP32-08H) repair

I have 7 of these in my shop all with the same symptoms except 1. The TVs turn on but then when you turn it off and back on the power supply will not start only clicks, all voltages fluctuate. if you unplug it for a while and plug it back up it will turn on again, but turn it off and try to turn it back on and back to clicking and no start. It acts like it is not holding a load. I have recapped the supplies, checked all diodes, and most all resistors with no luck. I have reflowed all the ring cracks and cold joints and have scoured the surface mounts for cracks, breaks, and bad joints but I am at a loss. Anyone have a solution for this problem?

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Hello everyone,
I have swapped one of these power boards (LGP32-08H) in a faulty TV, because someone has worked on it before me, and did a messy job. The TV works fine, but as curious as I am, wanted to repair this PSU.
I have ordered the replacement parts, soldered everything in place, but it has a weird symptom. T101 transformer ticks. It has a weird ticking sound, every second. Needless to say, it doesn't have steady output on the secondary side. Viewing with the scope, it reveals that the voltage rises about 20 percent over the nominal rail voltages (eg. 24VDC rail shuts itself down at around 30V) then the cycle repeats every second. I have changed so far the following: U102, Q110, Q111 (these drive T101), U600, Q601, Q602 (these drive the zero crossing detector L600), every optocoupler, and every capacitor that has anything to do with the VCC voltage of the ICs above. The only part I didn't touch is standby, because it is always steady, and from its transformer (T501) comes a switched 12V on the secondary side, which is also solid. Also replaced U251 (TL431), with no luck.
If someone could help me out, that would be great.
The schematic is found in the first comment.

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

What is the VCC voltage on U102 pin 12 and is it steady. ou should have VCC on Q114 collector and also the emitter if Q114 base is turned on
Were any of the parts you replaced bad? Were the fets shorted? if they were shorted are the gate drive diode and resistors ok.
Is the PFC ciruit working, what is the voltage on F101?

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

What is the VCC voltage on U102 pin 12 and is it steady. ou should have VCC on Q114 collector and also the emitter if Q114 base is turned on
Were any of the parts you replaced bad? Were the fets shorted? if they were shorted are the gate drive diode and resistors ok.
Is the PFC ciruit working, what is the voltage on F101?

R_J,
first of all, thank you very much for your time.
Voltage on F101 also fluctuates (385-405V) according to this ticking noise.
VCC voltage is 13V, and goes to 12.5 when this sound appears. So I can say, it also varies, but not so much. I have replaced C512 (main capacitor for VCC), but nothing changed. Nothing seemed bad before the replacement, but as I said, someone has already worked on this before. U102 were completely shorted, and R118-119 were 12K (on schematic they are 10K), so I changed everything back, according to schematic. Only the FETs are different, instead of 04N60 I only got 10N60, but this should not be a problem.
I made one interesting test. Changed U600 (SG6961SZ) to FAN6961, and now VCC is 15V, but U102 won't start T101. Strange, the two ICs should be the same. Have you seen such thing before?

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

It seems your vcc is too low, Q505 is the vcc switch and Q504 is the regulator, It has ZD504 16 volt zener on the base so you should have around +16 volts for you VCC to the ic's That 12.5~13 is just on the border of them running
U600 is the pfc boost driver ic, if you were getting 385~405 volts before, the ic was working. I suspect when you changed it now your pfc is no longer working. that would explain why your vcc came up also, no current draw by u600/u102.
You changed C512 but I would also change C511 & C510
What schematic are YOU using, the on from post #1 has R119 at 30Ω, R118 is 10k
Did you list the wrong number and that should have been R117 & R119?
If those resistors were bad, I suspect D116/117 and r119/120 may be bad also

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

It seems your vcc is too low, Q505 is the vcc switch and Q504 is the regulator, It has ZD504 16 volt zener on the base so you should have around +16 volts for you VCC to the ic's That 12.5~13 is just on the border of them running
U600 is the pfc boost driver ic, if you were getting 385~405 volts before, the ic was working. I suspect when you changed it now your pfc is no longer working. that would explain why your vcc came up also, no current draw by u600/u102.
You changed C512 but I would also change C511 & C510
What schematic are YOU using, the on from post #1 has R119 at 30Ω, R118 is 10k
Did you list the wrong number and that should have been R117 & R119?
If those resistors were bad, I suspect D116/117 and r119/120 may be bad also

With FAN6961 it won't start at all, but VCC goes as high as 15V. At the emitter of Q504 the voltage is 16.9V, so I would say it is okay.
As you said, something is not working around the PFC. I think I have narrowed it down to the zero crossing detector. So, in theory this PFC chip should "see" when the AC line is 0V and start a new switching cycle (if needed) to keep the voltage on the capacitors around 400V. BUT mine wants to start every second, and as I see on the scope, it doesn't recognize the zero crossing. I will try to figure out why, and if I succeed, I will write the results.
I am using the schematic from post #1, I may have wrote the worng position numbers before, but on the pcb I soldered them correctly. Yes, R117/118 are 10k, R119/120 are 30 ohm (well, in my case 33 ohm, because I couldn't find 30R anywhere). So as stated before, someone has worked on this, that's why I decided to change almost the whole neighbourhood of U102. Just to be clear, U102, Q110, Q111, R117/118, R119/120, D116/117 are brand new.

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

But your pfc circut WAS working before so why did you change U600? put back the original and get that circuit working again.
I suspect you are only getting about 325 volts on F101 now.

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

But your pfc circut WAS working before so why did you change U600? put back the original and get that circuit working again.
I suspect you are only getting about 325 volts on F101 now.

I wrote that the voltage also fluctuates (385-405V) so I was thinking the PFC was working, but only partly.
But now I have good news, there is some progress. I removed U102, and the voltage on the boost capacitors are rock steady 404V. This makes me believe that there is something wrong around U102 indeed.
Fun fact: the circuit still doesn't work with FAN6961. So here must I make a note, that SG6961SZ and FAN6961 are NOT interchangeable.

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

The pfc voltage could fluctuate when the U102 circuit was trying to start, that would be normal, with the U102 removed from the circuit there is no current being drawn at all so the main filter will charge to the boosted voltage and stay there.
I looked at the datasheets for the two SG and FAN ic's and they don't look to be that different.
Did you ever check the two diodes D116 & D117

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

The pfc voltage could fluctuate when the U102 circuit was trying to start, that would be normal, with the U102 removed from the circuit there is no current being drawn at all so the main filter will charge to the boosted voltage and stay there.
I looked at the datasheets for the two SG and FAN ic's and they don't look to be that different.
Did you ever check the two diodes D116 & D117

D116/117 are fine. They are both new, but to be sure, I removed them, tested, then soldered back on.

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Good news, everyone!

I found the bad component. It was ZD115, a 7.5V zener diode.
In my circuit it was a firm 80 Ohm resistor.
After replacing it, the PSU is up and running!
Thank you R_J for your help!

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Glad to here its working, I was going to suggest checking that part of the circuit next since you mentioned you had a higher than normal secondary voltage (24 ~ 30)
I had another look at the SG6961SZ and FAN6961 datasheets and don't see why the fan did not work, unless it is bad

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Glad to here its working, I was going to suggest checking that part of the circuit next since you mentioned you had a higher than normal secondary voltage (24 ~ 30)
I had another look at the SG6961SZ and FAN6961 datasheets and don't see why the fan did not work, unless it is bad

Thanks, I am also confused why the FAN6961 didn't do its job.
Both ICs were in original package, from a trustful distributor (TME).
There is still a chance it was DOA, but I won't test it further. It landed in my bin, and will be forgotten

[nomoresonys]

Re: LG PSU EAY40504401 (LGP32-08H) repair

So did that ZD115 read bad previously or was that the first time you tested it?

[yohnsee]

Re: LG PSU EAY40504401 (LGP32-08H) repair

So did that ZD115 read bad previously or was that the first time you tested it?

It was the first time I tested it. Actually, second time, because first I used my meter's continuity test, to see if something is shorted to ground. The problem with this method is that my meter only beeps if the resistance is below 50 Ohms. I don't always read the display, only listen for the beep, so I can make it faster. But this time it backfired

[frica]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Hello yohnsee:

Wondeful that you could repair the PSU!!

For the very newbie one in electronic repair, could you explain in detail how do you test the zener diode especially the regulator function?

I know that a zener is like a normal dode in forward polarization and as a regulator in inverse polarization. With a multimeter and the PBC no energized I know test the diode function. But how did you test the regulator function using a multimeter in ohm scale? or only tested if both ends of zener had very low ohmios?

do you test in ohmio scale o in diode scale? Do you test in circuit? did you test in forward polarization (positive probe in Anode and negative probe in catode) or/and inverse polizarization?

thank you!!

[R_J]

Re: LG PSU EAY40504401 (LGP32-08H) repair

Most zeners will check ok but might zener at the wrong voltage. First check them with diode test, but the only real test is there zener voltage and if it is correct.
Out of circuit, you can use a voltage supply that is a few volts higher than the zener diode and then supply the voltage to the zener through a resistor, sometimes a 1k or less will work. then measure the voltage across the zener. If you have a backlight led tester with voltage readout you can use it also.