Sharp LC37SB24u won't stay on

[jakeklem]

I need some help tracking down an issue with this set. I've found that a few of the CCFL are not lighting, but there are other issues it seems. I have the inverter board disconnected from the PSU. It will power on and I can see (with a flashlight) the menu flicker on the screen, but it only appears for a second. Then one of three things will happen. TV goes dead and I get the green blinking light, it will stay on but no menu, or it turns red then I get the amber light if I try to power it back on.

voltages on the PSU when it stays on:
13v: 13v
BU5v: 5v
PS_ON: 3v

Can anyone suggest a starting point on fixing this one?

[budm]

Re: Sharp LC37SB24u won't stay on

"I've found that a few of the CCFL are not lighting" It will only take one bad CCFL, or bad Inverter transformer or circuit to put the TV in protection mode, so if you know that it has bad CCFL, then you need to replace it or bypass the protection circuit at you own risk.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

Does it go into protection mode if the inverter is disconnected?

[budm]

Re: Sharp LC37SB24u won't stay on

Does it go into protection mode if the inverter is disconnected?

Do you mean the cables going to the inverter board are disconnected or the cables to the lamps?
It depends on the design.
You also need to look at the inverter board connectors to see if there are any labels for the pins to tell you what the pin's functions are.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

I mean the little bridge between the power board and the inverter is disconnected.
yes, there is labeling on the inverter board connection from the PSU. see attached picture.

Getting 64v on the 60v pins.

[CapLeaker]

Re: Sharp LC37SB24u won't stay on

Looks like we can see only every other pin out, not all of them. There is more behind the connector

[budm]

Re: Sharp LC37SB24u won't stay on

Please list all the pin names.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

Oops, I missed that. Here it is.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

How might I bypass the protection mode? I want to see if it will stay on without the CCFL.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

I get voltage after power on until it goes into protection mode. Here is the pin out to the inverter board:

GND 0
STB 3v
OFL 0
OSC 0
ERR 0
REGBRT 0
NC 0
ADMIN 0
NC 0
13V 13v
GND 0
NC 0
GND 0
GND 0
NC 0
GND 0
no label 0
NC 0
60v 64v
60v 64v
60v 64v
60v 64v

[CapLeaker]

Re: Sharp LC37SB24u won't stay on

if you disconnect the inverter from the PSU, does the TV work normal less the back light?

[budm]

Re: Sharp LC37SB24u won't stay on

if you disconnect the inverter from the PSU, does the TV work normal less the back light?

It does per post 1.
I do not see the BL-ON signal pin on that list of the pin out.
Also the dim control signals and other signals also showing 0V which do not look right.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

if you disconnect the inverter from the PSU, does the TV work normal less the back light?

Briefly yes, but it will not stay functional.

[jakeklem]

Re: Sharp LC37SB24u won't stay on

It does per post 1.
I do not see the BL-ON signal pin on that list of the pin out.
Also the dim control signals and other signals also showing 0V which do not look right.

Yes, good observation Bud. I wonder if the pin without a label might be BL-ON.

Any ideas for a starting point of what I can test? Is there a way I can fake out the circuit protection to make it act like the inverter is plugged in?

I haven't messed with backlights much. What would happen if I remove the ones that are not functioning and power it on?

[budm]

Re: Sharp LC37SB24u won't stay on

OK, I look at the inverter board picture at Shopjimmy, I see that it has a rectangular box fuse F7501, and also a bunch of power MOSFETs mounted on the heatsink, so you should check them out to see if any of the MOSFETs is shorted out or not.
http://www.shopjimmy.com/sharp-runtk...-inverter.htm#

[budm]

Re: Sharp LC37SB24u won't stay on

OK, this is what I found, I look up the power supply board at Shopjimmy:
http://www.shopjimmy.com/sharp-rdenc...upply-unit.htm
According to SJ, this power supply board is also used in LC-37D44U (the other 3 models do not have good service manuals for them).
So I found the service manual at ELEKTROTANYA:


Page 70 show the pinout of the LB connector, the STB (Von) is the BL-ON and you do have 3V there so BL-ON is OK.
You said you see blinking LED, so see the manual to see if the code match your blinking LED.
It is big manual and I did not have the time to look at everything in details yet.