Got one of these given to my in a "dead" state. Pwr supply checks out OK, but there is nothing at the BL_ON pin when powered up. What conditions must be met before the proper voltage appears at the BL_ON line?
I don't normally work on consumer stuff like this so my theory on LCD stuff is basically non existant. Display controller issue maybe?
Just an update on this. I removed all of the inverter transformers and found one with a bad primary winding that wouldn't ring. I put one of the good ones back in and still get no BL_ON voltage (I'm assuming this should be a 5v logic hi). Sounds like the driver circuit for the failed transformer was damaged and still throws it into error mode. Sound right?
A bad inverter transformer won't cause a problem until the backlight starts , then causing an error shutdown. Some inverter transformers (particularly the domino type) are easily damaged when removed from the board, so maybe you damaged the xfr when you pulled it. Any chance you're actually getting a very brief backlight on command?
When off, you should be getting a standby voltage of typically 5 or even 3.
3 volts from the power supply to the main. When you hit the power button, you should get an "on" signal from the main back to the power supply to tur n on the rest of the secondaries (such as 24 for the back light inverter bo ard). At some point, you'll get a backlight on signal for the inverter as well. Depending on manufacturers strategy, different things need to be acc omplished by the main before the backlight on command is sent.You can always jump the on command line to the 5v with a 470 ohm resistor a nd see what happens. YMMV...
That's how the majority of these things are configured. I guess in a weird situation, a shorted inverter transformer, used in a TV that runs it's 24V from the smps all the time could cause a problem on plug in, but I've neve r seen one configured that way.
ts, then causing an error shutdown. Some inverter transformers (particul arly the domino type) are easily damaged when removed from the board, so ma ybe you damaged the xfr when you pulled it. Any chance you're actually g etting a very brief backlight on command?
3.3 volts from the power supply to the main. When you hit the power butt on, you should get an "on" signal from the main back to the power supply to turn on the rest of the secondaries (such as 24 for the back light inverte r board). At some point, you'll get a backlight on signal for the invert er as well. Depending on manufacturers strategy, different things need t o be accomplished by the main before the backlight on command is sent.and see what happens. YMMV...
eird situation, a shorted inverter transformer, used in a TV that runs it's 24V from the smps all the time could cause a problem on plug in, but I've never seen one configured that way.
:No, there's nothing at the enable line at power up. Since a primary winding was bad I believe the driver IC for that section is damaged causing the feedback to disable the backlight. No transformers were damaged when removed, I checked them all with my Sencore LC77...thats how I found the bad one. I can verify this by scoping the primary side drive when forced on.
All other voltages are there. 24v,12v, 5v, and 5v stby.
then causing an error shutdown. Some inverter transformers (particularly the domino type) are easily damaged when removed from the board, so maybe you damaged the xfr when you pulled it. Any chance you're actually getting a very brief backlight on command?
volts from the power supply to the main. When you hit the power button, you should get an "on" signal from the main back to the power supply to turn on the rest of the secondaries (such as 24 for the back light inverter board). At some point, you'll get a backlight on signal for the inverter as well. Depending on manufacturers strategy, different things need to be accomplished by the main before the backlight on command is sent.
see what happens. YMMV...
situation, a shorted inverter transformer, used in a TV that runs it's 24V from the smps all the time could cause a problem on plug in, but I've never seen one configured that way.
I don't have an encyclopedic knowledge of all LCD TVs, but in my experience there usually was no feedback from the inverter to the main video board. The usual sequence goes something like this:
When the TV is plugged in the standby power supply (5v stby) comes up, which starts the standby controller (often a part of the main control IC). This may then briefly turn on the main power supply, check for problems, then turn off the main power supply. The standby controller then monitors the remote sensor and control buttons for an 'ON' command. When one is received the main power supply is turned on, a self test is run and if everything is OK the inverter enable line is driven high. If the self test fails typically an LED is flashed to indicate an error.
Typically the inverter is supplied by the manufacturer of the LCD panel, and several versions may be found on a given model. A quick search on eBay shows at least three different models of inverters, including one that was notorious for blowing drivers, and another that was notorious for failures of the transformers.
An additional point - some models of Sanyo are known to have a 'lock up' mode. If a failure is detected, they will shut dwon and refuse to restart until a particular reset sequence is entered via the remote.
One point you did not mention - does the power button on either the remote or the control panel switch the main power supply off and on? If it does, one technique I use is to hook a signal source (video game, DVD player) up to an input, turn the TV on, then use the input button to cycle through the inputs to see if sound is heard.
PlainBill
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