Sharp lc-42sb45u no response... at all.

[tibimakai]

Re: Sharp lc-42sb45u no response... at all.

I haven't taken photos yet. I will take some tomorrow. Do you need just the inverter's picture?
Here is one from shopjimmy until then:
http://www.shopjimmy.com/cmo-27-d026...t-inverter.htm

[budm]

Re: Sharp lc-42sb45u no response... at all.

I do not know if you have the pictures of this inverter board or not, can you tell me which post they are in? It sounds like you do have BL_ON OK.

[tibimakai]

Re: Sharp lc-42sb45u no response... at all.

So, I have checked some voltages and they all seem fine.
Not sure about the inverter and brightness voltages should be, but they are 3.2V both of them. It shouldn't be one of them higher then the other?
The inverter gets the 24.4V, fuses(2x) are good, but when I measure the VCC and VDD voltages to the two ICs(OZ964GN & BA2902F) I don't think they are getting any. The BA get's at pin #4 0,43V and the OZ gets 0V at pin #5.
Not sure on how to check the FET transistors on this inverter, they are the ones with five pins(4+1) P2204ND5G. The only voltages I'm getting is on the tab or center pin is the 24.4V and on S2 the same 24.4V. The others are 0V.


https://cdn.badcaps-static.com/pdfs/...4eb885fbd4.pdf
Just to refresh on what's going on with this TV, screen seems totally dead, but the green LED is on after the power cable is plugged in. That is normal? It shouldn't go in standby first(red LED)?

[budm]

Re: Sharp lc-42sb45u no response... at all.

That means the transistor of the PS_ON detection circuits on the power supply is getting enough Base current to turn it on, if you discconect that PS_ON from the main board and check the output voltage at the PS_ON pin on the main board, you will more likely to see something close to 5V.
For the backlight to turn on, it should have another signal called "BL_ON", or "INV_ON" from the main board that goes to the Inverter board.

[tibimakai]

Re: Sharp lc-42sb45u no response... at all.

Thank you for helping me. I'm about to start again on this TV, so it comes in time your comment.
I'm not expecting to get 5V, but at least 3.1-3.3V.
So what are you saying that there is no power supply issue if I get 1.75V for PS_ON and I'm getting all the voltages? Power LED is Green. Anything else is dead. No back light turns on at all, no picture at all, I don't know about sound since I can change anything.
Customer claimed a power outage before this happened.

[budm]

Re: Sharp lc-42sb45u no response... at all.

@tibimakai: Please see the attached picture. The PS_ON signal only have to be high enough voltage to supply the Base current to turn on the transistor in the power supply PS_ON signal detector in the power supply board.
As you can see, the PS_ON voltage level will not be 5V when the Power supply board is connected to the Mian board due to the resistor values.

[dood]

Re: Sharp lc-42sb45u no response... at all.

Just a followup on this thread... The problem was the mainboard in the TV. Bought a replacement from eBay, dropped it in, and hey presto, TV worked.

One thing that was very surprising to me... the speakers on this Sharp 42" TV are way worse than the ones in my 32" Philips.

[tibimakai]

Re: Sharp lc-42sb45u no response... at all.

I have just picked up almost the same TV, it's just a T at the end of the model number.
Green LED is on when the TV it's turned on, I have all the voltages, except the PS_ON it's 1.75V. How is that possible with this low voltage to have the 5V, 12V and 24V?
My standby voltage is the same 4.4V.
I will go through the suggestions above, but I don't understand how come I have all the voltages with this low voltage at PS_ON?
The seller stated that they used the TV in the morning and when they came home the TV did not turn on any more, but in this time they had a power outage. They had other electronic devices fail before and after this happened, like laptop screen went black, and so on, it could be a coincidence too.

[dood]

Re: Sharp lc-42sb45u no response... at all.

I don't believe you can tell much from the inverter pulling it down to 12 volts, since the inverter is not being turned on. We could try to trick the inverter on, but that can be pretty tricky, and does not work on all sets. It just depends on what control signals the inverter needs. Some need a control voltage, as well as inverter on command. Honestly, that would brobably be a waste of time, because we already know that the power board is never being turned on. The important thing is, you have demonstrated that the power board is functioning, and the supplies are trurning on and off with the proper control signal.

This information, coupled with the fact that your microprocessor is getting hot even though the unit is not turned on, tells me your issue is almost certainly on the main board.

Well, I don't have the money to buy a main board right now ($700 for tires on my truck... wtf?), so I will try recapping it, just for fun. It might make no difference at all, but it'll at least give me something to try until I can order a main board.

[randtek]

Re: Sharp lc-42sb45u no response... at all.

You are correct... with the power board unhooked, the 24v lines stay at 24v as long as the resistor is in place. I wasn't getting a steady connection before. Also, once the board is powered on, the 5v line comes up to a steady 5v instead of 4.4v.

With the power board hooked up to the inverters, the 24v rails drop to 12v, and I don't see the inverters light. There is a separate inverter power on line, though.

I don't believe you can tell much from the inverter pulling it down to 12 volts, since the inverter is not being turned on. We could try to trick the inverter on, but that can be pretty tricky, and does not work on all sets. It just depends on what control signals the inverter needs. Some need a control voltage, as well as inverter on command. Honestly, that would brobably be a waste of time, because we already know that the power board is never being turned on. The important thing is, you have demonstrated that the power board is functioning, and the supplies are trurning on and off with the proper control signal.

This information, coupled with the fact that your microprocessor is getting hot even though the unit is not turned on, tells me your issue is almost certainly on the main board.

[PlainBill]

Re: Sharp lc-42sb45u no response... at all.

You are correct... with the power board unhooked, the 24v lines stay at 24v as long as the resistor is in place. I wasn't getting a steady connection before. Also, once the board is powered on, the 5v line comes up to a steady 5v instead of 4.4v.

With the power board hooked up to the inverters, the 24v rails drop to 12v, and I don't see the inverters light. There is a separate inverter power on line, though.

THAT sounds like a problem. But keep it in mind while determining why PS_ON never goes high.

PlainBill

[dood]

Re: Sharp lc-42sb45u no response... at all.

The 24V rails should stay at 24V as long as the resistor from 5V to PS_ON is in place and AC power is applied. If it does not, there may be a problem with the power supply. Test the power supply under load to be sure.

PlainBill

You are correct... with the power board unhooked, the 24v lines stay at 24v as long as the resistor is in place. I wasn't getting a steady connection before. Also, once the board is powered on, the 5v line comes up to a steady 5v instead of 4.4v.

With the power board hooked up to the inverters, the 24v rails drop to 12v, and I don't see the inverters light. There is a separate inverter power on line, though.

[PlainBill]

Re: Sharp lc-42sb45u no response... at all.

Jumping from +5 to PSON with a 1k resistor resulted in the 24v rails coming up to spec, and then slowly dropping back to 0.00v. I'm guessing this means the power board is good?

The 24V rails should stay at 24V as long as the resistor from 5V to PS_ON is in place and AC power is applied. If it does not, there may be a problem with the power supply. Test the power supply under load to be sure.

PlainBill

[dood]

Re: Sharp lc-42sb45u no response... at all.

Jumping from +5 to PSON with a 1k resistor resulted in the 24v rails coming up to spec, and then slowly dropping back to 0.00v. I'm guessing this means the power board is good?

[dood]

Re: Sharp lc-42sb45u no response... at all.

randtek - don't worry about it! The paying job always comes first . I'll scrounge up a 1k resistor and give it a shot.

[randtek]

Re: Sharp lc-42sb45u no response... at all.

Hello again, sorry I took so long getting back, been too busy at work to reply. I can't afford to lose moy job!

With the power connector disconnected from the main board, connect the 5v stby line to the power on pin of the power connector through a resistor, I use about 1k ohms for this. Plug unit in, and see if the other power supplies come up. If not, try connecting the power on pin to ground, using the same resistor. If neither of these conditions cause your power board to turn on, your power board is probably bad. At this stage of the game, I believe the problem is not your power board, and we will try to prove that with these tests. I will get back to you mudch quicker next time.

[dood]

Re: Sharp lc-42sb45u no response... at all.

I sent randtek a PM the other day to see if he had any other advice. I think I'm just going to order a power board and see what happens.

[dood]

Re: Sharp lc-42sb45u no response... at all.

Just as another possible hint... the power LED is supposed to be red at standby and green at power-on. The LED on this TV is not lighting at all.

[Toasty]

Re: Sharp lc-42sb45u no response... at all.

Waiting on randtek to respond to your answers to his questions. I agree and don't see a problem either with the voltages on IC903.

[dood]

Re: Sharp lc-42sb45u no response... at all.

Looking at the datasheet for IC903 -

It appears that the output for those 3 pins is basically correct.

I've been all over the board and have found no burnt resistors or other components.

Anything else I can check?