Sharp Aquos 32"

[rigeback]

Why? Is the 3.3V on the t-con not present?

When I connect the screen with the ribbon connectors the t-con area goes dead at test points VCC3.3V, VCC1.5V, VGH35V and VGL-6V otherwise the board seems to work as it should???

[rigeback]

Take a 100 Ohm resistor, connect one side to any voltage rail that is more than 1.8V (for example, B+3.3V, BU+5V, or BU+3.3V, and etc.). Connect the other side of the resistor to pin 1 of IC1725. This should turn ON ANT+5V. If the TV still doesn't work, then I don't know.

So I hooked up 3.3V to IC1725 on pin 1 with 100 Ohm resistor although I see I'm only getting 1.75V on pin 1 maybe the resistor is wrong! I don't see any improvement to screen while connected to DVB box!

When I connect the screen with the ribbon connectors the t-con area goes dead at test points VCC3.3V, VCC1.5V, VGH35V and VGL-6V otherwise the board seems to work as it should???

Anyway the fact remains that when I connect the screen the t-con area goes dead including VLS 15V and close by D8403 & L8401. I followed the power lines on (Main 10/13 (POWER) Schematic Diagram) testing all the components and no joy, can't source the defective part!

[PlainBill]

Om several occasions I have encountered LCD displays that appeared to have a hole burned into the LCD panel. I concluded that something (a transistor?) in the panel itself had shorted, destroying itself and the surrounding area.

It certainly sounds like something like that has happened here.

PlainBill

[rigeback]

Originally Posted by PlainBill

Om several occasions I have encountered LCD displays that appeared to have a hole burned into the LCD panel. I concluded that something (a transistor?) in the panel itself had shorted, destroying itself and the surrounding area.

It certainly sounds like something like that has happened here.

PlainBill

Well I'm not sure thats the case here because I tried the screen while connected with 1 ribbon and bingo half the screen was working and then I managed to swap sides of the screen with the controler in total white mode and then to contrast. I checked the voltages and all were present in this trial. I admit I didn't get a picture but it seems the screen functions.

When I connected ribbon 2 I had a total white screen for a while and within 2 minutes the TV entered standby, restarted and its back to square one 0.60V power on the t-con and screen panel. Theres a short some where I think??

[rigeback]

New problem today! lamps don't come on and the TV goes into suspend mode shortly after switching on, with the screen connected or disconnected, No power coming from PSU, Fuses seem okay??? Looks like will have to remove the PSU to see the underside tomorrow

[rigeback]

Quick question regarding the PSU page 78 of the manual- FOR DISABLING PROTECTIONS AND BE ABLE TO REPAIR INVERTER, GROUND IC7500 PIN Nº1- I did this but there is still 36+ Volts on some of the caps etc?

[PlainBill]

Originally Posted by rigeback

Quick question regarding the PSU page 78 of the manual- FOR DISABLING PROTECTIONS AND BE ABLE TO REPAIR INVERTER, GROUND IC7500 PIN Nº1- I did this but there is still 36+ Volts on some of the caps etc?

That's what I would expect. You are disabling the protection so it continues to operate.

PlainBill

[rigeback]

Well that tells me a whole lot, so it will work now without testing or repairing anything!

[PlainBill]

Originally Posted by rigeback

Well that tells me a whole lot, so it will work now without testing or repairing anything!

Ehhhhh - it will work for a while. Then something will fail - maybe in a BAD manner.

Shortly after Edison invented the electric light bulb and people started using them in their homes someone decided that instead of buying an expensive fuse to replace the one that blew for no reason at all, he's just jumper it with a piece of wire. Shortly after that the local fire department put out their first electrical fire.

PlainBill

[rigeback]

Yeh well I don't want any fires in my house so I've removed the jumper and re tested the voltage out put which is correct while the green light is illuminated, the problem continues to be associated with suspend power on switching I believe!

[rigeback]

Well it seems I've lost all the high voltages on the board 5 Volts Max, back to the
ANT+5V rail IC1703 which is receiving the 5V but the out put is 0.80 the spec says 4.8V pin5 and 3.8V pin1.
Of course this depends on if Mr. Momaka or someone wants to continue trouble shooting with me otherwise we can call it quits, no worries!
The immediate root cause could be easier to identify at this stage and removing IC1703 or other IC's for testing out of circuit might be the answer.

[rigeback]

Please can some one help with this PSU since it was working well before a timer kicked in and shut down the back lights and 12V main board supply.
I would like to also know how to test the fly back switching transformer in case it has a problem?
The PSU still powers up with the red led on although when I switch on it goes to green briefly and and back to red, when its green there is 12 volts!

[momaka]

Sorry for the delay, rigeback. I've just been very busy with school and work and so I haven't had much time to dig more deeply into the circuit diagrams for your PSU. I'll see if I can find something in them later this week, hopefully.

[rigeback]

No problem, I've been reading a fair bit about this switching device although I am still trying to figure out what malfunctioned to not reset the timer, it could be the fly back transformer which I still have to remove from the board to test.

[rigeback]

Does the power board upside down have to be grounded to the TV chassis to attain the correct high voltages, i.e 400V on both ends of the buck cap? I seem to have lost high voltage on PFC circuit!

[momaka]

Originally Posted by rigeback

Does the power board upside down have to be grounded to the TV chassis to attain the correct high voltages, i.e 400V on both ends of the buck cap? I seem to have lost high voltage on PFC circuit!

Nope. Should still be there even without it.

[rigeback]

Got all the required voltages on the board but no 400V, I think theres a problem with the PFC controller or 400 V rectifier as the voltages fluctuated a fair bit, PFC ON/OFF is working.

[tom66]

Many power supplies will not switch on PFC in standby. The bulk cap will remain at around 325V in standby.

[rigeback]

I guess the PFC controller is not getting the signal from the power supply controller to release the latch, will follow the lines again tomorrow. Found this interesting pdf regarding back light failure due to one specific cap with a crack, I checked mine and it tests good!

[rigeback]

Got problems here, when I boot up the power board with the red standby led ON going to green the voltage surges to around 1900V for a few seconds and then back 20 volts at the PFC inductor inlet / outlet, while in standby mode this 20V is measured at 220V inlet up to PFC inductor and around.
Could this be a faulty EMI filter, resistor or AC Brown Out?