Yesterday, out of the blue, our 42" Sanyo DP42848 LCD stopped working. No lighting strikes or anything, it just stopped working properly. It's out of warranty.
When turned on, we see a black screen with the blue "HDMI1" input notification in the corner: the screen appears to be uniformly lit, so it sure looks like the LCD and backlighting are all working properly. A few seconds later, at the point where it would normally start showing video, the backlights turn off and sound comes on. If I shine a light in, it looks like the LCD is showing video, but it has no lighting. Sometimes, it just simply turns itself off, which might have been my troubleshooting triggering some other safety.
I did a bunch of googling, followed troubleshooting steps posted by others in this forum and in the service manual one of you posted (thanks!!). I'll try to summarize here, but I'm kinda stumped at this point.
No obvious burnt components on the PSU, mainboard or inverter boards, and no capacitors are bulging or leaking. The HV side of the inverter transformers looks ugly, but it's hard to tell if it's burnt or just resin.
Power Supply: with cables unplugged, I measured 24V to one of the inverter boards and 5V to ground on CN2. I'm unable to measure 24V to the other inverter board or 12 or 24V on CN2, but I suspect it's because power is intentionally turned off when they're unplugged. I was able to measure 12V and 24V to ground on mainboard on solder points near K8B, so I'm pretty sure at this point the power supply is OK.
Main board: While the TV is running (sound, etc.) I'm getting 5V on IC800 pin 32 consistantly. I've had difficulty measuring it on pin 23, at some times measuring 0V, 3.5V, and 5V, but finally was consistently measuring 5V when sound was on. Might have been my error reading a wrong pin, or might have been while the TV was in standby or some sort of limp mode.
Inverter boards: only thing I've found so far is that the HV side of the transformer nearest the edge of the board has no continuity between terminals on either board. The inboard transformer on both sides does have continuity. I measured 0.2Ohms on the LV side of each transformer between 3-4, & 4-5, but open circuits between 2-3 and 6-7. All were consistently like this. Is this my the problem or is it a red herring? I've not yet tested voltages on the inverter boards with the TV turned on due to all the shielding in the way.
What's my next step?
When turned on, we see a black screen with the blue "HDMI1" input notification in the corner: the screen appears to be uniformly lit, so it sure looks like the LCD and backlighting are all working properly. A few seconds later, at the point where it would normally start showing video, the backlights turn off and sound comes on. If I shine a light in, it looks like the LCD is showing video, but it has no lighting. Sometimes, it just simply turns itself off, which might have been my troubleshooting triggering some other safety.
I did a bunch of googling, followed troubleshooting steps posted by others in this forum and in the service manual one of you posted (thanks!!). I'll try to summarize here, but I'm kinda stumped at this point.
No obvious burnt components on the PSU, mainboard or inverter boards, and no capacitors are bulging or leaking. The HV side of the inverter transformers looks ugly, but it's hard to tell if it's burnt or just resin.
Power Supply: with cables unplugged, I measured 24V to one of the inverter boards and 5V to ground on CN2. I'm unable to measure 24V to the other inverter board or 12 or 24V on CN2, but I suspect it's because power is intentionally turned off when they're unplugged. I was able to measure 12V and 24V to ground on mainboard on solder points near K8B, so I'm pretty sure at this point the power supply is OK.
Main board: While the TV is running (sound, etc.) I'm getting 5V on IC800 pin 32 consistantly. I've had difficulty measuring it on pin 23, at some times measuring 0V, 3.5V, and 5V, but finally was consistently measuring 5V when sound was on. Might have been my error reading a wrong pin, or might have been while the TV was in standby or some sort of limp mode.
Inverter boards: only thing I've found so far is that the HV side of the transformer nearest the edge of the board has no continuity between terminals on either board. The inboard transformer on both sides does have continuity. I measured 0.2Ohms on the LV side of each transformer between 3-4, & 4-5, but open circuits between 2-3 and 6-7. All were consistently like this. Is this my the problem or is it a red herring? I've not yet tested voltages on the inverter boards with the TV turned on due to all the shielding in the way.
What's my next step?
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