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Toshiba Satellite Pro 400CDT - Only works on battery, not AC

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First post, by jnnelson79

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Hello!
As the title says, my Toshiba Satellite Pro 400CDT has an issue... it only runs on battery. Luckily, I have a battery that works. If I take the battery out and plug in the AC, the AC power light won't come on, and the laptop won't boot or do anything. When I put a charged battery into the machine and plug in the AC, then the AC light comes on, and the laptop starts showing that it's charging (even though it isn't). Then, I can boot the system and use it normally for an hour or two, and then, even if the AC cord it plugged in, the laptop will die from a dead battery and not boot again until you swap in a charged battery.

So, my first thought was to replace the power supply. I tested the voltages on the old supply, and they seemed good, but I figured maybe it was just a problem with the charge circuitry. So, I went ahead and swapped in a new power supply (correct part, double and triple checked). However, when I powered the computer on, the same issues occur as stated above. Nothing will work on the laptop unless a battery is plugged in.

Any ideas? I bought the new (not really new) power supply from an Ebay seller who claimed it was good, but perhaps it wasn't? It was very difficult getting all the way down to the power supply, and unfortunately, lots of little plastic clips broke on the case that had to be glued back on. Therefore, if I open it again, I want to have a very solid plan first. I just assumed naively that swapping the power supply would fix it.

What do you all think?

Reply 1 of 3, by Thermalwrong

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I'm not sure how it could have happened since the AC > DC PSU adapter is integrated, but could it have burned out the DC power input fuse on the mainboard?
See these pictures here of a close relative for reference: Re: Toshiba Satellite Pro 420CDT
and Re: Toshiba Satellite 200CDS 810 - troubleshooting and general info (KBC error - trying to solve, help needed)

Check for a large-ish white rectangular fuse just by where the red & blue DC cable plugs into the motherboard and make sure of whether that still has continuity or not

Be safe when testing since there are mains on parts of it, but I do recommend verifying that the DC cable from the AC > DC PSU is outputting around 15 volts, not 18v. Red wire is positive and blue is negative. There are two versions and the 400CDT should only work off the 15v PSU, the 18v PSU is for the T2100 series and a few other weird ones.

To avoid breaking clips, read the 400cdt maintenance manual. Process for disassembly is carefully remove the keyboard holder strip, remove keyboard, loosen the video card and leave the cables connected to it. Then undo the screws holding the top case on top&bottom, once all the screws are removed, pull the top half + screen away from the bottom half, starting at the back of the laptop and 'hinging' on the front. It should come away without any clips breaking.

Reply 2 of 3, by jnnelson79

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Thermalwrong wrote on 2024-06-11, 02:20:
I'm not sure how it could have happened since the AC > DC PSU adapter is integrated, but could it have burned out the DC power i […]
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I'm not sure how it could have happened since the AC > DC PSU adapter is integrated, but could it have burned out the DC power input fuse on the mainboard?
See these pictures here of a close relative for reference: Re: Toshiba Satellite Pro 420CDT
and Re: Toshiba Satellite 200CDS 810 - troubleshooting and general info (KBC error - trying to solve, help needed)

Check for a large-ish white rectangular fuse just by where the red & blue DC cable plugs into the motherboard and make sure of whether that still has continuity or not

Be safe when testing since there are mains on parts of it, but I do recommend verifying that the DC cable from the AC > DC PSU is outputting around 15 volts, not 18v. Red wire is positive and blue is negative. There are two versions and the 400CDT should only work off the 15v PSU, the 18v PSU is for the T2100 series and a few other weird ones.

To avoid breaking clips, read the 400cdt maintenance manual. Process for disassembly is carefully remove the keyboard holder strip, remove keyboard, loosen the video card and leave the cables connected to it. Then undo the screws holding the top case on top&bottom, once all the screws are removed, pull the top half + screen away from the bottom half, starting at the back of the laptop and 'hinging' on the front. It should come away without any clips breaking.

Thank you! This is very helpful! I did try to follow the manual, but the clips were very brittle, especially on the screen bezel (I had to replace the inverter card due to a really bad whining noise... not related to the PSU).

Anyway, I will definitely check those voltages. I was very confused myself about why this was happening. It's a strange problem to be sure.

Thanks!

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