LG 32LH500B - No power, no standby

[JeffJ]

No power no standby LED.

Fuse ok, 154-155V across the caps.

Doesn't seem to be outputting 12v or 24v and thus no standby.

Any ideas?

[JeffJ]

Re: LG 32LH500B - No power, no standby

I decided to remove the transformer to and wire in a separate supply to the 12v 24v and gnd on the secondary side and the tiv fires up and works perfect.

So the issue is on the Primary side im just not good enough to figure out what.


Any help would be great! thanks a lot!

[budm]

Re: LG 32LH500B - No power, no standby

Can I see good clear straight shots picture of the whole bottom side of the board?

[JeffJ]

Re: LG 32LH500B - No power, no standby

Can I see good clear straight shots picture of the whole bottom side of the board?

sure here it is.

[budm]

Re: LG 32LH500B - No power, no standby

I cannot read the P/N of that SMPS IC U0D1?.
Can you tell me what it is?

[JeffJ]

Re: LG 32LH500B - No power, no standby

U0D1 is "LNK6777K"

[budm]

Re: LG 32LH500B - No power, no standby

U0D1 is "LNK6777K"

OK, I look up the spec sheet, see attached PDF.
BTW, is this really LG TV? It looks like Skyworth re-badged TV which is junk and they can charge more by putting LG tag on them.
Also, is that Boost converter board or Buck converter board connected to bench power supply?

[JeffJ]

Re: LG 32LH500B - No power, no standby

OK, I will look up the spec sheet.
BTW, is this really LG TV? It looks like Skyworth rebadged TV which is junk and they can charge more by putting LG tag on them.
Also, is that Boost converter board or Buck converter board connected to bench power supply?

I'm sure its a re-badge, it feels very RCA like. It's not one of their flagships, but it is branded LG and has the LG software on it. I'm just looking to fix it on the cheap and give it to the local scouts to use in their club house.

and the buck converter is also connected to the bench supply. I had to step 24v down to 12v. But it does indeed fully function when i bypass the primary side and power the secondary on the bench supply.

I believe i found a service manual, but again I'm not skilled enough to utilize it.

LG+32LH500B+Chassis+6M69N.pdf

Edit" ill have al ook at the data sheet you sent see if i can figure out a place to start from. thanks

[budm]

Re: LG 32LH500B - No power, no standby

Just check DCV of the BP pin against S pin, it should be about 5.7V.
The spec sheet explain what each pin of the IC is for.
BTW, you are working in the HOT deadly side of the circuit so at least plug the TV into GFCI outlet and do not touch anything in the hot dies with your hands or body.

[JeffJ]

Re: LG 32LH500B - No power, no standby

Just check DCV of the BP pin against S pin, it should be about 5.7V.
The spec sheet explain what each pin of the IC is for.
BTW, you are working in the HOT deadly side of the circuit so at least plug the TV into GFCI outlet and do not touch anything in the hot dies with your hands or body.

Thanks Budm, I'll give it a go tomorrow and post back. My workshop is all GFI so thats covered.

[budm]

Re: LG 32LH500B - No power, no standby

BTW, what power consumption does it show on the back of the TV where the model number tag is?

[JeffJ]

Re: LG 32LH500B - No power, no standby

BTW, what power consumption does it show on the back of the TV where the model number tag is?

120vac 1.2A

[JeffJ]

Re: LG 32LH500B - No power, no standby

Just check DCV of the BP pin against S pin, it should be about 5.7V.
The spec sheet explain what each pin of the IC is for.
BTW, you are working in the HOT deadly side of the circuit so at least plug the TV into GFCI outlet and do not touch anything in the hot dies with your hands or body.

VDC of the BP pin against S pin is 2.7VDC SO assumption is the LNK6777K is faulty?

[budm]

Re: LG 32LH500B - No power, no standby

VDC of the BP pin against S pin is 2.7VDC SO assumption is the LNK6777K is faulty?

If you look at spec sheet figure #3, the BP pin is the output pin of the 5.75V internal Voltage regulator fed by Voltage from D pin, so check and see if you do have about 160VDC at the D pin.
Low Voltage reading on the BP pin can be due to bad internal regulator, too heavy load on the BP pin, so check the resistance between BP and Source pin to see what you get. Also check the bypass capacitor connected to the BP pin.
BTW, so the tag says 120VAC 1.2A, that will be 144VA, that power supply is not rated that high I am surprised it lasts that long.

[JeffJ]

Re: LG 32LH500B - No power, no standby

Resistence between BP and S is 68.4Kohm

Bypass cap doesnt appear to be bad is 460 NF

D pin is 159.6VDC and do is across the caps (it has gone up 5vdc) i Removed the LNK6777K from the board to do these tests.

I might roll the dice and try the LNK6777K i have here.

[budm]

Re: LG 32LH500B - No power, no standby

Resistence between BP and S is 68.4Kohm

Bypass cap doesnt appear to be bad is 460 NF

D pin is 159.6VDC and do is across the caps (it has gone up 5vdc) i Removed the LNK6777K from the board to do these tests.

I might roll the dice and try the LNK6777K i have here.

I would try new IC.
The IC has exposed pad for heatsinking so it will take quite a bit of work to remove it from the copper plane.
They copper plane used for heatsinking looks too small to dissipate the heat for that much power, you may want to add heatsink using thermal conductive epoxy to attach a heatsink to the IC.

[JeffJ]

Re: LG 32LH500B - No power, no standby

I would try new IC.
The IC has exposed pad for heatsinking so it will take quite a bit of work to remove it from the copper plane.
They copper plane used for heatsinking looks too small to dissipate the heat for that much power, you may want to add heatsink using thermal conductive epoxy to attach a heatsink to the IC.

Same symptoms with the new LNK6777K

VDC across the caps has dropped back down to 155VDC and BP is outputting 2.7.

So I'm missing something else here. with the lnk in circuit, the VDC is doping so low that what you suggested previously that its not outputting 5.7vdc on the BP.

Once i get this working i will indeed sync the IC

[budm]

Re: LG 32LH500B - No power, no standby

According to the block diagram of the IC, it is just a simple 5.75V regulator.
If you look at figure 11 in the spec sheet, can you see if it has resistor like R9 that you can disconnect and also see if BP pin goes some where else too.
According to page 4, the value of the BP cap program the protection mode. I wonder if it goes into protection mode.
The rectifier diodes on the cold side are OK?

[JeffJ]

Re: LG 32LH500B - No power, no standby

According to the block diagram of the IC, it is just a simple 5.75V regulator.
If you look at figure 11 in the spec sheet, can you see if it has resistor like R9 that you can disconnect and also see if BP pin goes some where else too.
According to page 4, the value of the BP cap program the protection mode. I wonder if it goes into protection mode.
The rectifier diodes on the cold side are OK?

thank you! i will do as you instruct and report back when i do.

[JeffJ]

Re: LG 32LH500B - No power, no standby

The rectifier diodes on the cold side seem to be ok, I have a 3K resistor in place (ROD9) which appears to be R9 in Figure 11. I can try removing that tomorrow when i get back to my tools.

I have a diode close to ROD9 that seems to give me a reading both ways (Z0D5) in diode mode on my meter, Z0D2 and Z0D1 dont give me readins both ways.

I've attached a close up of the area front and back.