Sharp LC-45GX6U wont power on

[vorius]

My Television just has a red light under "POWER" which blinks every 4-5 seconds. No other lights. If I try to turn on the power either via remote or the button on the television itself there is no response. Just the same blinking red light.

I opened up my TV and I visually inspected the exposed circuit boards. I see no sign of leaking, bulging or otherwise deformed capacitors. I also looked at the fuses particularly the fuse which is on the same circuit board the power cable plugs into and it is fine.

I would like to next plug the power in and test voltages are key contacts along the power supply route to make sure those two boards are functioning properly. I just don't know what voltages I should be seeing in the output from the second larger board - the one with 3 transformers and 4 large capacitors. How can I found out this information? Are there any technical documents to help me (which are available online - free) ?

I did find an awesome guide someone linked to on the fixya forums which had great photos and instructions for diagnosing LCD tv problems however for the life of me I cannot find it again!

[vorius]

Re: Sharp LC-45GX6U wont power on

Update- I did find the schematics diagrams and service manual online for free. I checked them out and I was following instructions in the troubleshooting section for "no power-up" where front LED does not change from red to blue. I got to the point where I am testing voltages at plug P1701 and P1702 and it's not matching what they specify - On P1701 I only see pin 6 with 6V, pin 11 with 2.5V and pin 12 with 2.4V. No discernible voltages in any other pin. According to this flowchart in the service manual, should be 1.8V at pin 6, 3.3V pins 8 and 9, 5V on pin 12.

Then on P1702 I am only seeing voltage on pin 7 at 6V, which matches what they are looking for - however in 8 has nothing but in manual they say 6V (unless I am misunderstanding it, It may be that it is supposed to be paired with pin 7 so only pin 7 is hot while this one is the ground?) So far I am not having any luck trying to determine if it's a problem on the "CS Power Unit" or the main "Power Unit". I can only determine that the "Line Filter Unit" is functioning properly as it has 120V coming out of it into the "Power Unit".

[vorius]

Re: Sharp LC-45GX6U wont power on

Can anyone help me with some terminology from the service manual?

for example it mentioned testing specified voltage at: "S-Vcc+15V (pins (11) and (12) of PA/P1752)"

I can find the plug labelled P1752 but what does the "PA" in front refer to? I can find the pins 11 and 12 on this plug but does that mean I test the voltage by putting one contact on one pin and the other contact on the other pin or that BOTH pins should be 15V? I usually test voltages by putting one contact on what I want to test and the other on ground.

Then for the voltage itself it apparently needs to be 15V but what does S-Vcc mean?

I'll continue to tinker with this but so far it looks like if I am doing this right then I am not getting the right voltages on the CS Control Unit board and I probably should replace it (cost $40). But I'd like to be sure I understand all this terminology.

Also what do they mean by "MOS-FET" and "normal" in the sentence "Are MOS-FET (Q1701, Q1702, Q1703, Q1704 and Q1705) and IC1952 normal?" IC1701 = the CS control unit board

[PlainBill]

Re: Sharp LC-45GX6U wont power on

Can anyone help me with some terminology from the service manual?

for example it mentioned testing specified voltage at: "S-Vcc+15V (pins (11) and (12) of PA/P1752)"

I can find the plug labelled P1752 but what does the "PA" in front refer to? I can find the pins 11 and 12 on this plug but does that mean I test the voltage by putting one contact on one pin and the other contact on the other pin or that BOTH pins should be 15V? I usually test voltages by putting one contact on what I want to test and the other on ground.

Then for the voltage itself it apparently needs to be 15V but what does S-Vcc mean?

I'll continue to tinker with this but so far it looks like if I am doing this right then I am not getting the right voltages on the CS Control Unit board and I probably should replace it (cost $40). But I'd like to be sure I understand all this terminology.

Also what do they mean by "MOS-FET" and "normal" in the sentence "Are MOS-FET (Q1701, Q1702, Q1703, Q1704 and Q1705) and IC1952 normal?" IC1701 = the CS control unit board

I'm a lot better at figuring these things out in context. You're right, the terminology can be confusing.
Vcc is the power for the ICs. The S prefix probably means 'Standby'; it's present even when the TV is off.

+15V - The voltage you should see, usually within 5% or 10%

(pins (11) and (12) Obviously, the pin numbers. They are probably connected together.

of PA/P1752) PA probably refers to the board designation. Some companies assign names to board, others use letter or number designations. And P1752 refers to the connector designation.

MOS-FET is a type of transistor. Normal would probably mean no visible signs of damage.

PlainBill

[vorius]

Re: Sharp LC-45GX6U wont power on

Thanks for the information PlainBill!

I am a bit stumped now at what to do. I realized couple days ago that I was looking in the wrong part of the manual for troubleshooting power problems - I was looking in the section for the external AVC box!

But the section for the TV itself is terrible. Its a short brief section for "Power supply error" and goes like this:

1. When turning on the power, pin (19) of IC2203 remains 3.3V.

Yes? Check IC4804 and its peripheral circuits.

No? Proceed to 2)

2. The output of pin (5) of IC4807 is 5V

No? Check IC4807 and its peripheral circuits.

And that's all.

Seems a bit too concise to me, first of all these microprocessors mentioned (IC2203, IC4804, IC4807) are on one board - the main computer of the TV called the top unit controller. But to get to this point power from the outlet would have passed through 3 power supply boards - the line filter board, the actual power supply board with its big transformers and big capacitors and then the CS Power Unit board which I believe routes the low voltages among some other tasks.

But there is no process described to rule out any problem on these boards. I find that odd.

Doing things on my own I traced my input voltage into the main power supply board (ruling out any problem with the line filter board) and then testing the output of the power supply board. But I can only really test one output voltage (6V going towards the monitor microprocessor known as IC2203) because the other 4 12V outputs and 4 15v outputs would not be active until the TV''s computer trips the "TVPOW" switch to call for that power. I wish I could trip that manually so I can test those voltages and rule out the power supply unit as having any problems. I think this should be easy to do though because I've done it for PC motherboards just making a connection between two pins.

Anyway getting back to the troubleshooting flowchart, I found IC2203 which has about 64 tiny contacts surrounding it and of them I found pin 19 but it's voltage was 0. The next pin over (pin 18) had 3.3V. What's odd is when I look at a diagram of this circuit on the service manual it has "0" next to both of these pins but shows "3.3" next to pin 17 instead, which was also 0 for me. I am certain I have the pin numbers correct, they are labeled clearly.

Then as hard as it was to make a contact to a precise pin on this chip IC4807 would be impossible as its pins are so much smaller and are so tight next to each other. On top of that it's on the underside of the board so it is extremely difficult to access. If it turns out to also not have the correct voltage I dont know what it means by "Check IC4807 and its peripheral circuits". I suppose since I dont have the ability to replace one of these microprocessors I'd need to replace the whole board? But where is the process to rule out a problem with the power supply boards in the first place?

If this turns out to be a problem on this top controller board it would be one of the more expensive boards to replace ($157) but the worst thing is it's got so many connections to it and some of the connections are these delicate flat ribbon connections I have no idea how to operate. I am afraid I will damage them just by trying to pull them out somehow

Think I might just give up on this and trash the whole unit. I was hoping it was a simply problem with the power supply board but it's not clear what the problem is. I could try replacing this top controller but its a gamble at this point since I am not confident I can determine it is the part a fault.

[vorius]

Re: Sharp LC-45GX6U wont power on

wow didn't have any time to look at my tv for quite a few days now. Tonight I spent 15 minutes on the power supply unit. I learned how to trip the switch to the power supply by connecting two contacts so it outputs full power to all its pins as if the TV turned on. All the pins tested ok - 4 plugs 15V an 4 12V just as described in the schematics show. so I think its safe to say the power supply unit is fine, no?

That leaves two possible culprits in my opinion: the dc/dc converter and the top controller.

the top controller is the main computer pcb, and the one i'd dread replacing the most not only because it is most expensive but most complicated with so many plugs

Since I am not sure how exactly to rule out the dc/dc converter since I am not sure under what circumstances it is supposed to output voltage stated in schematics I am thinking I will try replacing it first since its relatively cheap at $45. If it doesnt help then I replace the top controller at $160.

good plan?

I dont think any of the other components would lead to this problem - namely the 4 inverter boards, the board handling video inputs, the switch board, audio plugs... right? I would imagine if those components had a failure I'd see different symptoms?

[PlainBill]

Re: Sharp LC-45GX6U wont power on

wow didn't have any time to look at my tv for quite a few days now. Tonight I spent 15 minutes on the power supply unit. I learned how to trip the switch to the power supply by connecting two contacts so it outputs full power to all its pins as if the TV turned on. All the pins tested ok - 4 plugs 15V an 4 12V just as described in the schematics show. so I think its safe to say the power supply unit is fine, no?

That leaves two possible culprits in my opinion: the dc/dc converter and the top controller.

the top controller is the main computer pcb, and the one i'd dread replacing the most not only because it is most expensive but most complicated with so many plugs

Since I am not sure how exactly to rule out the dc/dc converter since I am not sure under what circumstances it is supposed to output voltage stated in schematics I am thinking I will try replacing it first since its relatively cheap at $45. If it doesnt help then I replace the top controller at $160.

good plan?

I dont think any of the other components would lead to this problem - namely the 4 inverter boards, the board handling video inputs, the switch board, audio plugs... right? I would imagine if those components had a failure I'd see different symptoms?

I can't make any suggestions until I at least see a picture of the DC-DC converter board. I have not worked on enough Sharp TVs to understand the function of the DC-DC converter board. The TVs I have worked on all incorporate that into the main board (small signal board), and the outputs are all 'live' if the main power supply is on, but designs vary.

I would suggest seeing if the service manual specifies the output voltages of the DC-DC converter, and checking if they are correct BEFORE replacing it.

PlainBill

[vorius]

Re: Sharp LC-45GX6U wont power on

I can't make any suggestions until I at least see a picture of the DC-DC converter board. I have not worked on enough Sharp TVs to understand the function of the DC-DC converter board. The TVs I have worked on all incorporate that into the main board (small signal board), and the outputs are all 'live' if the main power supply is on, but designs vary.

I would suggest seeing if the service manual specifies the output voltages of the DC-DC converter, and checking if they are correct BEFORE replacing it.

PlainBill

Good day PlainBill!

Thanks for replying.

Yeah that would definitely make the most sense, it's just that I am not sure how to determine if stated voltage in the service manuals schematics are supposed to be constant or only when the unit is actually powered up.

For example on this DC/DC board the schematic shows that for plug P1702 pins 1-4 carry 12V. But if I tested it now they are all zero because the TV is not actually asking for that power from the power supply. It's not getting to that state. I'd have to force it by tripping the circuit again like I did when the power supply was isolated. I'd have to do it now while this DC/DC board is plugged into it.

IF you have the time (and ~67 megs of free space!) the PDF of the service manual is available for free download from this site:



I'm looking at pages D159-D162 for this DC/DC board's schematic

[PlainBill]

Re: Sharp LC-45GX6U wont power on

Good day PlainBill!

Thanks for replying.

Yeah that would definitely make the most sense, it's just that I am not sure how to determine if stated voltage in the service manuals schematics are supposed to be constant or only when the unit is actually powered up.

For example on this DC/DC board the schematic shows that for plug P1702 pins 1-4 carry 12V. But if I tested it now they are all zero because the TV is not actually asking for that power from the power supply. It's not getting to that state. I'd have to force it by tripping the circuit again like I did when the power supply was isolated. I'd have to do it now while this DC/DC board is plugged into it.

IF you have the time (and ~67 megs of free space!) the PDF of the service manual is available for free download from this site:



I'm looking at pages D159-D162 for this DC/DC board's schematic

It's not the space, it's the motivation. At this point I'm supposed to be fixing a balky ML17AS (AKA 170MP), resoldering the battery holder in a Thinkpad R30, rebuilding the filter for the goldfish pond, and killing the weeds that have taken advantage of the cooler weather to flourish. I'll be downloading the manual now.

PlainBill

[PlainBill]

Re: Sharp LC-45GX6U wont power on

As closely as I can determine, IC2203, the monitor microprocessor issues the ON signal which turns on both the main power supply and the DC / DC converter.

No, I am NOT positive about this; I'm not even sure I would be confident enough to order a main board. If I read this correctly, the TV is 6 years old.

PlainBill

[vorius]

Re: Sharp LC-45GX6U wont power on

It's not the space, it's the motivation. At this point I'm supposed to be fixing a balky ML17AS (AKA 170MP), resoldering the battery holder in a Thinkpad R30, rebuilding the filter for the goldfish pond, and killing the weeds that have taken advantage of the cooler weather to flourish. I'll be downloading the manual now.

PlainBill

Haha, thanks

As closely as I can determine, IC2203, the monitor microprocessor issues the ON signal which turns on both the main power supply and the DC / DC converter.

No, I am NOT positive about this; I'm not even sure I would be confident enough to order a main board. If I read this correctly, the TV is 6 years old.

PlainBill

Yeah it's going to hit 5 years this month. Is there any way I could rule out some of the other components, like the inverter boards for example? I suppose if an inverter board has a problem it could be causing the microprocessor to stay in this error state as well. I wonder how it would response if I unplugged them all... but then, would a perfectly working tv go into the same error state if it detects the inverter boards are not plugged in? I suppose so but a different error code (different flashing red power led pattern).

Will tinker around more tomorrow!

Thanks for your help!

[PlainBill]

Re: Sharp LC-45GX6U wont power on

Haha, thanks



Yeah it's going to hit 5 years this month. Is there any way I could rule out some of the other components, like the inverter boards for example? I suppose if an inverter board has a problem it could be causing the microprocessor to stay in this error state as well. I wonder how it would response if I unplugged them all... but then, would a perfectly working tv go into the same error state if it detects the inverter boards are not plugged in? I suppose so but a different error code (different flashing red power led pattern).

Will tinker around more tomorrow!

Thanks for your help!

I would definitely say the inverter is NOT the cause of this problem.

The common way a plasma or LCD TV works is the power supply consists of two parts - the standby supply and the main supply. The standby supply provides power to the standby processor, the remote sensor circuits, and if present, the cable card. If the pwer cord is plugged in, the standby processor is running. When the standby processor senses the power button has been pressed on either the remote or the control panel it turns on the main main supply. Since that never happens, the problem is with the standby processor and associated circuits.

Actually, I got ahead of myself. Verify that the appropriate signal is passed to the main board when the power button on the control panel is pressed. Also, check the IR sensor to see if the remote is being detected.

PlainBill

[vorius]

Re: Sharp LC-45GX6U wont power on

I would definitely say the inverter is NOT the cause of this problem.

The common way a plasma or LCD TV works is the power supply consists of two parts - the standby supply and the main supply. The standby supply provides power to the standby processor, the remote sensor circuits, and if present, the cable card. If the pwer cord is plugged in, the standby processor is running. When the standby processor senses the power button has been pressed on either the remote or the control panel it turns on the main main supply. Since that never happens, the problem is with the standby processor and associated circuits.

Actually, I got ahead of myself. Verify that the appropriate signal is passed to the main board when the power button on the control panel is pressed. Also, check the IR sensor to see if the remote is being detected.

PlainBill

Excellent suggestion! I have been using the actual power button on the set itself to rule out any IR/remote problems. But based on your experience can you tell which pin I need to monitor for a voltage that is supposed to be sent to the microprocessor to turn the tv on?

Looking at IC2203 there are quite a few possible candidates:

TV_POW
TV_POW2
STBY_POW
PANELPOW
SMPOW
DDC_POW


I am thinking it is STBY_POW from trying to follow it though. So I should see 3.3V on pin 14 when I press power on?

[PlainBill]

Re: Sharp LC-45GX6U wont power on

Excellent suggestion! I have been using the actual power button on the set itself to rule out any IR/remote problems. But based on your experience can you tell which pin I need to monitor for a voltage that is supposed to be sent to the microprocessor to turn the tv on?

Looking at IC2203 there are quite a few possible candidates:

TV_POW
TV_POW2
STBY_POW
PANELPOW
SMPOW
DDC_POW


I am thinking it is STBY_POW from trying to follow it though. So I should see 3.3V on pin 14 when I press power on?

Two pins should show activity. OPC is the optical input from the remote receiver. It comes to pin 1 of IC2203. I would expect a change in level when a button on the remote is pressed. STBY_POWER should drop to 0 volts when the power button on the front panel is pushed.

PlainBill