Samsung T240HD 24" LCD monitor. Backlight never comes on, not even a flash. Flashlight shows menus etc. working fine.
See pictures for measurements I made.
Connected each of the four backlight CCFLs individually to another inverter and they run for a quarter second, then turn off. They seem to be running stably for that quarter second, not just flashing for a brief instant when struck by the inverter. I think that they turn off here because they aren't in the metal case that the inverter is in or don't match the characteristics of the inverter, not because there is something wrong. Regardless, light comes out of them for a noticeable amount of time, which doesn't happen with the T240HD's inverter. In the T240HD there is no flash at all, and no sound like it's trying to strike them either.
I tested the capacitance of the two large 1000uF capacitors on the 15V supply for the inverter section, and they are about their rated 1000uF, so fine there.
Small transformers at corners measure 136 ohms on both sides of each.
Supplies at 9-pin connector measure a tad high: 15.86V for 15V supply, and 5.31V for 5.2V supply. Maybe because backlight isn't running.
Main inverter transformer has two secondaries, both measure 1.042k. It seems to have two primaries, both in parallel (as the SEM2005 datasheet example shows), and <1 ohm resistance.
Dual MOSFET (U202, 4506GEH) has no less than 500K between gates and source/drains (and resistance grows as I hold leads, suggesting capacitors in parallel, not a leaky gate).
The three (clamp?) diodes on either side between the CCFL plugs and SEM2005 circuitry check ~0.5V one way, open the other way.
The SEM2005 (U201, datasheet) gets 15.86V power (pin 10). Enable (pin 11) starts out low, then goes high after a few seconds when power melody plays. The enable line connects to the logic board via a 9.25k resistor (R234). The signal in is 4.78V, and after the resistor, 3.79V to the SEM2005. On the datasheet it shows that pin16 is a 5V reference, but on the chip it measures only 0.56V (I've triple-checked this measurement) and tends to start around 0.46V then climp up to 0.56V. Nothing seems to be connected to the reference, so I wonder whether the chip is fried. The front shows what seems to be heat-related surface changes. With the meter on frequency mode, I don't measure any oscillating signals out of it. POUT (pin 8) is at 15.86V, and NOUT (pin 7) at 0V, so it's not turning the FETs on. This chip is only a few dollars on eBay, but I want to get some indication that it's really bad, and perhaps some indication that nearby circuitry hasn't damaged it.
See pictures for measurements I made.
Connected each of the four backlight CCFLs individually to another inverter and they run for a quarter second, then turn off. They seem to be running stably for that quarter second, not just flashing for a brief instant when struck by the inverter. I think that they turn off here because they aren't in the metal case that the inverter is in or don't match the characteristics of the inverter, not because there is something wrong. Regardless, light comes out of them for a noticeable amount of time, which doesn't happen with the T240HD's inverter. In the T240HD there is no flash at all, and no sound like it's trying to strike them either.
I tested the capacitance of the two large 1000uF capacitors on the 15V supply for the inverter section, and they are about their rated 1000uF, so fine there.
Small transformers at corners measure 136 ohms on both sides of each.
Supplies at 9-pin connector measure a tad high: 15.86V for 15V supply, and 5.31V for 5.2V supply. Maybe because backlight isn't running.
Main inverter transformer has two secondaries, both measure 1.042k. It seems to have two primaries, both in parallel (as the SEM2005 datasheet example shows), and <1 ohm resistance.
Dual MOSFET (U202, 4506GEH) has no less than 500K between gates and source/drains (and resistance grows as I hold leads, suggesting capacitors in parallel, not a leaky gate).
The three (clamp?) diodes on either side between the CCFL plugs and SEM2005 circuitry check ~0.5V one way, open the other way.
The SEM2005 (U201, datasheet) gets 15.86V power (pin 10). Enable (pin 11) starts out low, then goes high after a few seconds when power melody plays. The enable line connects to the logic board via a 9.25k resistor (R234). The signal in is 4.78V, and after the resistor, 3.79V to the SEM2005. On the datasheet it shows that pin16 is a 5V reference, but on the chip it measures only 0.56V (I've triple-checked this measurement) and tends to start around 0.46V then climp up to 0.56V. Nothing seems to be connected to the reference, so I wonder whether the chip is fried. The front shows what seems to be heat-related surface changes. With the meter on frequency mode, I don't measure any oscillating signals out of it. POUT (pin 8) is at 15.86V, and NOUT (pin 7) at 0V, so it's not turning the FETs on. This chip is only a few dollars on eBay, but I want to get some indication that it's really bad, and perhaps some indication that nearby circuitry hasn't damaged it.
Attached Files
I screwed myself over several times when ignoring the direction my nose pointed me to.
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