LG 32LN578V - Picture; No Backlight

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Removed C811 measured between pin8 and pin4 I get 5.50 ohms in 20K range .
Measured across pads where C811 sat 5.46 ohms in 20K range

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

You need to find where that low resistance is coming from and if necessary remove the IC.

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Now I am using a black star 3210 battery may be running low
what is strange is when I measure resistance between pin8 and pin4 red lead on pin4 black lead on pin8 in 20K range I get 5.50ohms if I reverse leads black lead on pin4 and red lead on pin8 in 20K range I get 11.50ohms.
and the same across C811 5.46 ohms red on one pad black on other pad if I reverse leads I get 11.56 ohms is this right or is my meter plying up ?

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

I think it's best to change the batteries and have confidence in your meter. However the REF outputs 5V at a maximum of 10mA. So if the REF was 5V and the load was 10 ohms then as you can see the maximum current from the REF output would be 0.5 Amps!!!!

Internal 5V Low Dropout Regulator
The MAP3202 has LDO embedded in it to supply Internal
analog, logic circuit and external REF Pin. This LDO operates
at a voltage level where Vcc is higher than the UVLO voltage. It
provides maximum 10mA of output current through regulator
which has 2% accuracy of performance.
To stabilize the voltage of REF Pin, it is recommended to use
low ESR capacitor which is as low as 1uF and connect it
between REF and GND Pin, and install it as close as to Pin.

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Have changed the batteries
In 20K range measured between pin8 and pin4 I get 3.42ohms

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Just measured the volt on pin8 with the C811 removed in 20v range on St/By 0.00v on switch on goes to 5.05v
So it would seem that C811 is short.
Would it cause any damage if I re-connected P801 led connection and switched TV on to see if backlights came up with this C811 removed ?

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

I believe at this point you need to lift the IC to rule it in or out as the problem.

Edit
I should have read your reply better. Leave the IC alone since you say that with C811 out, REF = 5V which is what it should be so all you need to do is replace the capacitor. I don't know what value it should be. Do you have the power supply schematic

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Do you mean remove it and send for a replacement to try ?
And not to power up with it in and C811 removed ?

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

Do you mean remove it and send for a replacement to try ?
And not to power up with it in and C811 removed ?

Just edited post #47

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

vinceroger69 supplied a link in post #21
That was all I had it does not have values for the capacitor.
I need to find a schematic for this power supply and source where to get this capacitor from ?
Then I can see if this cures the fault ?

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

I don't think it would hurt to power up briefly and check to see that the backlights come on.

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Wow I just re-connected the P801 led plug and powered the set up for a couple of seconds and yes the backlights came on what a result!!
I need to pop out in a while but when I come back I will try and locate a schematic for the power supply and where to obtain these caps from ?

Thank you so much for your help with this dick barton and vinceroger69 enjoyed working on this set and thank you to anyone else who contributed towards this issue.
I will keep you posted on how I get on with it.

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

You could try a 1.0uF or 0.47uF smd capacitor in it's place.

[vinceroger69]

Re: LG 32LN578V - Picture; No Backlight

in post 39 i added a picture from a lg service manual with the same ic being used so the capacitor on the same line as the ic pin should be the same value i guess ? it does have the values printed

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

The schematic part numbers as seen in the photo of the circuit board in post #1 that I've been referring to, do not appear to match up with the schematic you posted?

Ron...... do your board components numbering match up with the photo in post #1 or the schematic as forwarded by vinceroger69. If they match the schematic then the capacitor appears to be 0.47uF 16V

[vinceroger69]

Re: LG 32LN578V - Picture; No Backlight

the trouble is in post one someone else started this thread then ron started his fault finding in post 20 and has never added his own pictures so his board may not be a exact match like you say if different revision numbers etc, i found the schematic by just searching the psu board number so not sure if like you say it matches 100% due too different revisions etc, and the picture in post 39 is from a different lg led set but used the same ic and had capacitor values printed so thought it may help, but in your post 53 you had already guessed it was probably around this value so hopefully although maybe slightly wrong schematic the replacement capacitor will sort the issue out im not sure if thats a picture of rons own pcb in post 38 but that capacitor certainly looked darker etc

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

Yes you are right vinceroger69 I had not added any pictures as the ones posted seem to match.
And on the schematic you posted in #39 had the same map3202 ic but the smt caps and resisters had different ref numbers.
After searching for the schematic for my board in google a post came up for badcaps for a new member (Ad-M) and in his thread post #8 he supplied a schematic and in that schematic the ref numbers matched all my components on my board.
So I am quite confident that it is a 0.47uf 16v OR 25v just not sure on physical size unless (K 1608 X7R ) refers to the size.

[ronhayes]

Re: LG 32LN578V - Picture; No Backlight

I have located the parts locally and in his info he list case size as
case code in 0805
case code mm 2012

[vinceroger69]

Re: LG 32LN578V - Picture; No Backlight

I have located the parts locally and in his info he list case size as
case code in 0805
case code mm 2012

i maybe wrong but i think (K 1608 X7R ) means
C = Standard. Two significant digits and number of zeros. J = ±5%. K = ±10%. M = ±20% ... This option is limited to EIA 0603 (1608 metric) case size devices.

so maybe
http://www.ebay.co.uk/itm/10-X-CAP-M....c100677.m4598
or cpc but they now have a £5.00 minimum order
http://cpc.farnell.com/avx/0603yd474...x5r/dp/CA07662
try rs components or cpc etc im not sure if wiltsgrove in river street birmingham will sell them

[dick_barton]

Re: LG 32LN578V - Picture; No Backlight

smd sizes