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Old 09-05-2020, 02:48 PM   #1
cyclones
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Join Date: Feb 2010
City & State: Ames Iowa USA
Line Voltage: 120VAC 60Hz
Posts: 69
Default Toshiba blank screen, won't run without battery

Model is p745-s4320. I am looking at this for a friend. It came to me with a melted adapter plug. Not sure if this was caused by power fluctuations from the midwest derecho. I assumed there was damage to the power jack in the laptop too.

Before investing much time on it, I soldered leads to the motherboard and connected to my bench power supply. When I supplied 19 volts, I was able to power the computer on and see the Toshiba logo and BIOS messages on the screen. I believe there was no battery connected at the time.

I ordered a used Toshiba genuine power adapter and a replacement DC jack. For whatever reason, the end of the cable opposite the jack did not plug into the motherboard, but was soldered on, which I didn't realize until I went to replace it. It looked similar to the ones that plug into a jack on the motherboard.

I desoldered the old jack and soldered in the new one. Once I got everything back together, I tried it and found two things:
1. It won't start without the battery, even though the AC power LED is on. When the battery is in and the computer is plugged into power, AC power LED is on, and the battery charging LED is also on.
2. When I press the power button, the fan spins briefly, which is normal behavior for laptops I have worked with. But then it sits there and does nothing. I also tried the external VGA connection, and nothing shows up there either.

I don't know if the two problems are related or a coincidence.

I have tried removing the battery and holding power for 30 seconds, then replacing and using the key combination fn-f5-power, which I found suggested in a youtube video, but that doesn't make any difference.

I have checked points on the motherboard, and on battery I can find 12V, 5V and 3.3V rails. They all seem to be powered up.

I'm also not sure if this problem resulted from my work replacing the DC jack/cable or if there were issues with the laptop when I received it. I think my next step might be to resolder leads and check with my bench power supply to see if it will power up without battery with that power source. Other than that, I'm not sure what to try next.

Can anyone offer suggestions?
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