Toshiba L500 - the tale of the overprotective protection
This one ate up my whole day yesterday... Had this in for a NB replacement (client had done his homework). It would reboot by itself when it was supposed to show the welcome screen.
I tried reinstalling Windows on another hard drive and using VGA. As soon as it loaded the video driver it either rebooted or showed very distorted video. Gave the Intel NB a blast of hot air, no change. So i figured it must be faulty. Replaced NB and stupor.... same thing.
I started checking voltages, and found that the 1.05v supply to the NB dropped to 0.8 or 0.76V when it tried to load the driver. Replaced the PWM chip TPS51117, no change. Replaced the inductor, still no change. I wanted to replace the mosfets but figured that it'd be just as useless, so i downloaded the datasheet and focused on what the PWM was doing. Drive waveforms were ok, output ripple normal, so it had to be current limiting for some reason. Checked output for shorts, could not find anything.
I found the resistor for the TRIP pin to be 14.65K, exactly as per the mainboard schematic. Replaced with a 10K and it had 0.76v from the start, it didn't even POST anymore. That means i lowered the current limit instead of increasing it. Replaced again with a 36K, got a steady 1.05v. Got display, starting windows... and it booted!
Nothing's getting hot and the laptop works great.
There was nothing wrong with the board, it just used a little more power than it should have. Beats me why, but that's what it did. Just a heads up if you happen to run into the same issue.
I will attach pics as soon as i get back home.
I tried reinstalling Windows on another hard drive and using VGA. As soon as it loaded the video driver it either rebooted or showed very distorted video. Gave the Intel NB a blast of hot air, no change. So i figured it must be faulty. Replaced NB and stupor.... same thing.
I started checking voltages, and found that the 1.05v supply to the NB dropped to 0.8 or 0.76V when it tried to load the driver. Replaced the PWM chip TPS51117, no change. Replaced the inductor, still no change. I wanted to replace the mosfets but figured that it'd be just as useless, so i downloaded the datasheet and focused on what the PWM was doing. Drive waveforms were ok, output ripple normal, so it had to be current limiting for some reason. Checked output for shorts, could not find anything.
I found the resistor for the TRIP pin to be 14.65K, exactly as per the mainboard schematic. Replaced with a 10K and it had 0.76v from the start, it didn't even POST anymore. That means i lowered the current limit instead of increasing it. Replaced again with a 36K, got a steady 1.05v. Got display, starting windows... and it booted!
Nothing's getting hot and the laptop works great.There was nothing wrong with the board, it just used a little more power than it should have. Beats me why, but that's what it did. Just a heads up if you happen to run into the same issue.
I will attach pics as soon as i get back home.
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