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

[retiredcaps]

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

Anyone have anything else for me to try? ?

Waiting on results from post #32 from Toasty.

[dood]

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

Although the energy saving may be a factor, as randtek eludes to, I rather doubt it. The manual is way too specific.

If you check the troubleshooting guide on page 33 of the SM, it specifically asks about the presence of the +5 volt line and what to check if not present.

IMO, recapping the mainboard is a waste of time, until you get the PSU fixed.

My suspects here are the zeners ZD910 or ZD911, the switcher IC903, or the cap at C969. Also check any chip resistors of <500Ω value for burns or discoloration, like R991(47Ω) or R976 (22Ω).

What is the voltage across the mains cap C907? (strangely, no one asked this question...?)
Should be present at the anode of ZD911 (junction T904 - pin1/C945/ZD911).

Toast

I'm reading main cap voltage at 170.9VDC. I have 85.8VDC across C945 and ZD911

ZD910 has 5.1v...

[Toasty]

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

ZD911 is a 160v TVS diode (surge suppressor). That looks fine.

ZD910 is a 15v zener, but without the other parts working, tough to tell if that's a problem or not. Are resistors R976 & R991 okay?

What do you read from Pins 1, 2, & 4 of IC903 to ground (pins 5, 6, 7, 8)?

Toast

[dood]

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

ZD911 is a 160v TVS diode (surge suppressor). That looks fine.

ZD910 is a 15v zener, but without the other parts working, tough to tell if that's a problem or not. Are resistors R976 & R991 okay?

What do you read from Pins 1, 2, & 4 of IC903 to ground (pins 5, 6, 7, 8)?

Toast

IC903

Pin 1 - 1.0VDC
Pin 2 - 6.0VDC
Pin 4 - 171.6VDC

[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?

[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.

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.

[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.

[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.

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

[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?

[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.

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.

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

[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.

[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.

[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.

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.

[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.

[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.