Acoustic solutions LCD26761HDF no backlight

**tom66** · 03-06-2012, 11:35 AM

Re: Acoustic solutions LCD26761HDF no backlight

17PW20 isn't the same as 17PW26 unfortunately.

**sienoki** · 03-06-2012, 11:42 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

17PW20 isn't the same as 17PW26 unfortunately.

I know its not the same but just thought some of the components where in same place..theres abit floating about google about them 3 resistors in paralell

**tom66** · 03-06-2012, 11:50 AM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

I know its not the same but just thought some of the components where in same place..theres abit floating about google about them 3 resistors in paralell

Maybe there are some similarities, but I wouldn't rely on it. Did you check those diodes I mentioned?

**budm** · 03-06-2012, 12:19 PM

Re: Acoustic solutions LCD26761HDF no backlight

There is no SOURCE resistor for sensing, it is connected to the two jumpers to ground, the sensing circuit is cone some where else, see the PDF. Gates has resistors that you can see in the PDF.
I have a feeling that the components on the leaft side has something to do with start/stop control of the IC, the application notes does not show anything for start/stop function.
Tom is correct abouit the diagram, it is not the same as your baord as you cam see from the trace layout.

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**tom66** · 03-06-2012, 12:45 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

There is no SOURCE resistor for sensing, it is connected to the two jumpers to ground, the sensing circuit is cone some where else, see the PDF. Gates has resistors that you can see in the PDF.
I have a feeling that the components on the leaft side has something to do with start/stop control of the IC, the application notes does not show anything for start/stop function.
Tom is correct abouit the diagram, it is not the same as your baord as you cam see from the trace layout.

I'm going by what I've seen in other app notes but there is usually a resistor connecting the source pin to the -ve of capacitor to act as a current sense. To detect short circuits but also to provide a slow-charge of the main bulk capacitors and on some designs it makes the power supply current-mode controlled instead of voltage-mode.

**sienoki** · 03-06-2012, 12:58 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

I'm going by what I've seen in other app notes but there is usually a resistor connecting the source pin to the -ve of capacitor to act as a current sense. To detect short circuits but also to provide a slow-charge of the main bulk capacitors and on some designs it makes the power supply current-mode controlled instead of voltage-mode.

My probes touched together on ohms settings reads 01.0..which 2 diodes are you refering to tom..thx

**budm** · 03-06-2012, 01:00 PM

Re: Acoustic solutions LCD26761HDF no backlight

Some how this company is doing something else. I still believe it has something to do with those components on the top left. The sensing may be some where else.

**budm** · 03-06-2012, 01:02 PM

Re: Acoustic solutions LCD26761HDF no backlight

I would like to be able to trace out those parts to see if they are connected to pin 2 and 3 of that IC.

**sienoki** · 03-06-2012, 01:18 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

I would like to be able to trace out those parts to see if they are connected to pin 2 and 3 of that IC.

Are these pics any good..thx
http://i1068.photobucket.com/albums/...5/P1000885.jpg

http://i1068.photobucket.com/albums/...5/P1000884.jpg
http://i1068.photobucket.com/albums/...5/P1000890.jpg

**budm** · 03-06-2012, 01:31 PM

Re: Acoustic solutions LCD26761HDF no backlight

You had the better pictures before that I download but I still cannot see some of the traces that run under the components.

**sienoki** · 03-06-2012, 01:42 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by budm

You had the better pictures before that I download but I still cannot see some of the traces that run under the components.

From pin 2 & 3 i can see 2 traces..pin 2 trace goes to J159..pin 3 trace goes to 6801 smd resistor
http://i1068.photobucket.com/albums/...5/P1000892.jpg
http://i1068.photobucket.com/albums/...5/P1000894.jpg

**tom66** · 03-06-2012, 02:01 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

My probes touched together on ohms settings reads 01.0..which 2 diodes are you refering to tom..thx

The two big diodes with MUR... written on them on the photo with the big power resistor.

**sienoki** · 03-06-2012, 02:08 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

The two big diodes with MUR... written on them on the photo with the big power resistor.

D882 & D883 measure .387 & OL..thats in circuit shall i pull 1 leg..thx

**tom66** · 03-06-2012, 02:29 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

D882 & D883 measure .387 & OL..thats in circuit shall i pull 1 leg..thx

Nope seems okay.

Did you check the FETs for shorts too? Though *usually* if a FET is shorted it will blow a fuse, on a two switch forward converter it might not.

**sienoki** · 03-06-2012, 02:49 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Nope seems okay.

Did you check the FETs for shorts too? Though *usually* if a FET is shorted it will blow a fuse, on a two switch forward converter it might not.

Which FETS tom Q813 & Q814? if so how do i test..is it out of circuit & red & black on the 3 pins..
Sorry for not knowing the terms for components as im totally new at this..im a slow learner..lol

**tom66** · 03-06-2012, 03:09 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Which FETS tom Q813 & Q814? if so how do i test..is it out of circuit & red & black on the 3 pins..
Sorry for not knowing the terms for components as im totally new at this..im a slow learner..lol

Just check any and all combinations for shorts (<100 ohms) in circuit.

**sienoki** · 03-06-2012, 04:39 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Just check any and all combinations for shorts (<100 ohms) in circuit.

Q813 markings P9NK50ZFP
GK1QC V6
CHN 842
All six cobinations where OL apart from B-D & R-S that was 2.702m

Q814 markings F M J05
FQPF
9N50C
Same results but B-D & R-S was 2.522m
These where measured out of circuit..how do you know if these are shorted thx

**tom66** · 03-06-2012, 04:53 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by sienoki

Q813 markings P9NK50ZFP
GK1QC V6
CHN 842
All six cobinations where OL apart from B-D & R-S that was 2.702m

Q814 markings F M J05
FQPF
9N50C
Same results but B-D & R-S was 2.522m
These where measured out of circuit..how do you know if these are shorted thx

Seems fine, but what's B and R?

**budm** · 03-06-2012, 05:09 PM

Re: Acoustic solutions LCD26761HDF no backlight

I think I figure out how the IC is being turn on/off, see the PDF.

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**sienoki** · 03-06-2012, 05:10 PM

Re: Acoustic solutions LCD26761HDF no backlight

Originally posted by tom66

Seems fine, but what's B and R?

G S
D being gate/sorce & drain B black probe & R red probe testing on ohms.
Testing on diode/resistance mode i got on Q813 R-S..BD 1 beep .523 & reverse OL all other combinations being OL
On Q814 1 beep .510 on same S-D & OL reverse..are these ok then tom so i can solder back in..thx

Acoustic solutions LCD26761HDF no backlight

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