Acoustic solutions LCD26761HDF no backlight

**sienoki** · 03-04-2012, 07:08 PM

Re: Acoustic solutions LCD26761HDF no backlight

Heres a pic..thx
http://i1068.photobucket.com/albums/...5/P1000843.jpg

**budm** · 03-04-2012, 07:19 PM

Re: Acoustic solutions LCD26761HDF no backlight

OK, the next step is to find out if the PIN 1 (VDD) of the FAN7711 is getting the voltage feeding it, I have a hard time tracing out where it goes to in the pictures.

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**sienoki** · 03-04-2012, 07:32 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

OK, the next step is to find out if the PIN 1 (VDD) of the FAN7711 is getting the voltage feeding it, I have a hard time tracing out where it goes to in the pictures.

Does this pic help..thx
http://i1068.photobucket.com/albums/...5/P1000846.jpg

**budm** · 03-04-2012, 07:48 PM

Re: Acoustic solutions LCD26761HDF no backlight

I saw that picture but not sure if pin 1 is connected to R976, JUMPER J152 and then goes down some where in the bottom right of the picture, we just need to verify if we do have DC power feeding the VDD PIN1 of the IC or not.

**sienoki** · 03-04-2012, 07:55 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

I saw that picture but not sure if pin 1 is connected to R976, JUMPER J152 and then goes down some where in the bottom right of the picture, we just need to verify if we do have DC power feeding the VDD PIN1 of the IC or not.

How am i testing pin1..tv on black probe ground screw red pin1..thx
Im getting 14.96vdc with tv on

**budm** · 03-04-2012, 08:05 PM

Re: Acoustic solutions LCD26761HDF no backlight

Black lead to the ground pin4 (GND) of the IC, Red probe to pin 1 (VDD), just do not touch ANY METAL PART OF THE PROBE OR CHASSIS DURING THIS MEASUREMENT IN CASE YOU SLIP SINCE WE ARE WORKING ON THE AC PRIMARY SIDE OF THE CIRCUIT!

**sienoki** · 03-04-2012, 08:14 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

Black lead to the ground pin4 (GND) of the IC, Red probe to pin 1 (VDD), just do not touch ANY METAL PART OF THE PROBE OR CHASSIS DURING THIS MEASUREMENT IN CASE YOU SLIP SINCE WE ARE WORKING ON THE AC PRIMARY SIDE OF THE CIRCUIT!

It measures 15.00vdc

**budm** · 03-04-2012, 10:13 PM

Re: Acoustic solutions LCD26761HDF no backlight

And It is not there when you turn off the power switch? The 15vdc is correct since there is 15V Zener inside the IC.
At this point, it can be the IC is bad since it has the voltage but not sending out the drive signals (PIN 5, 7) to the two Gates of the MOSFET's. One thing I am not sure what those components on the left top corner are for yet. If you do have the 400Vdc feeding the MOSFET's, then I would try new IC.

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24vdc drive.pdf (318.9 KB, 107 views)

**sienoki** · 03-05-2012, 06:21 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

And It is not there when you turn off the power switch? The 15vdc is correct since there is 15V Zener inside the IC.
At this point, it can be the IC is bad since it has the voltage but not sending out the drive signals (PIN 5, 7) to the two Gates of the MOSFET's. One thing I am not sure what those components on the left top corner are for yet. If you do have the 400Vdc feeding the MOSFET's, then I would try new IC.

Thx for your time & being patient with me..im getting 392vdc measured with fluke..theres this repair kit..do i need it all?
http://www.chsinteractive.co.uk/elec...3-q814-s-c.htm
I cant find the IC830 FAN7711 in my farnells catolouge..thx

**tom66** · 03-05-2012, 07:10 AM

Re: Acoustic solutions LCD26761HDF no backlight

eBay: http://www.ebay.co.uk/sch/i.html?_fr...All-Categories

**sienoki** · 03-05-2012, 07:57 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

eBay: http://www.ebay.co.uk/sch/i.html?_fr...All-Categories

Thx tom..should i recap all the board or just try this IC first..ive been reading about the 4 block caps 2 red & 2 grey..thx

**tom66** · 03-05-2012, 08:03 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Thx tom..should i recap all the board or just try this IC first..ive been reading about the 4 block caps 2 red & 2 grey..thx

Try that for now as it will eliminate a possible cause.

**sienoki** · 03-05-2012, 08:22 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Try that for now as it will eliminate a possible cause.

Thx fella..ordered the IC will get back to you guys when installed..thx

**sienoki** · 03-06-2012, 06:57 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Thx fella..ordered the IC will get back to you guys when installed..thx

IC came today still no backlight..where to next?..thx

**tom66** · 03-06-2012, 07:29 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

IC came today still no backlight..where to next?..thx

Any big resistors connected to the source pin of the MOSFET? Can't see them from your pic. Might be O/C.

**sienoki** · 03-06-2012, 08:07 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Any big resistors connected to the source pin of the MOSFET? Can't see them from your pic. Might be O/C.

Hi tom..do these pics help..thx
http://i1068.photobucket.com/albums/...5/P1000867.jpg
http://i1068.photobucket.com/albums/...5/P1000872.jpg
http://i1068.photobucket.com/albums/...5/P1000871.jpg
http://i1068.photobucket.com/albums/...5/P1000873.jpg

**sienoki** · 03-06-2012, 08:38 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Hi tom..do these pics help..thx
http://i1068.photobucket.com/albums/...5/P1000867.jpg
http://i1068.photobucket.com/albums/...5/P1000872.jpg
http://i1068.photobucket.com/albums/...5/P1000871.jpg
http://i1068.photobucket.com/albums/...5/P1000873.jpg

Is it the 2 smd resistors 103 & 330 if so they measure Q813-103=10.2 & 330=33.7 in circuit
Q814-103=10.03 & 330=34.0
The big resistor R971-red-red-silver-gold which is 0.22 only measures 00.8 thats in circuit shall i pull 1 leg..thx

**sienoki** · 03-06-2012, 08:50 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Is it the 2 smd resistors 103 & 330 if so they measure Q813-103=10.2 & 330=33.7 in circuit
Q814-103=10.03 & 330=34.0
The big resistor R971-red-red-silver-gold which is 0.22 only measures 00.8 thats in circuit shall i pull 1 leg..thx

Do i need the other items in this kit..thx
http://www.ohmsupplies.co.uk/17PW26-...-Q813/Q814-S/C
R971 1 leg pulled reads 02.4 is this O/C..thx

**tom66** · 03-06-2012, 11:16 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Is it the 2 smd resistors 103 & 330 if so they measure Q813-103=10.2 & 330=33.7 in circuit
Q814-103=10.03 & 330=34.0
The big resistor R971-red-red-silver-gold which is 0.22 only measures 00.8 thats in circuit shall i pull 1 leg..thx

Probably not the SMDs, R971 is likely the sense resistor. Don't worry about pulling it for now, what does you meter read when the leads are touched?

Also check the two diodes for s/c looks like it's a two-switch forward converter. Big improvement on the old half-bridge Vestel designs which had huge reliability problems.

C878 could also be faulty but unlikely just looks like a snubber.

**sienoki** · 03-06-2012, 11:31 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Probably not the SMDs, R971 is likely the sense resistor. Don't worry about pulling it for now, what does you meter read when the leads are touched?

Also check the two diodes for s/c looks like it's a two-switch forward converter. Big improvement on the old half-bridge Vestel designs which had huge reliability problems.

C878 could also be faulty but unlikely just looks like a snubber.

Tom ive come across this what do you think..the 3 resistors in parallel r817-818-819..ive got 3 new same value from another kit that i didnt need...
When it mensions D861-Q841 & C904 they are print side right alongside the 24vpin out & thatD861 marking AP has readings both ways as i mentioned earlier in this thread..thx

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Vestel 17PW20 have shematic.doc (21.0 KB, 63 views)

Acoustic solutions LCD26761HDF no backlight

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