Electronics > Repair

Toshiba satellite a300 laptop

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Bukurat:
I have a Toshiba a300 that runs ok on battery but refuses to start when the AC adaptor is plugged in. If it's running and the AC adaptor is plugged in it immediately reboots. I did a search on the symptoms and found the culprit is usually the NEC/TONKIN capacitor that bypasses the power rail at the CPU.

I found disassembly instructions on the 'net and disassembled the laptop so I could remove the capacitor. After removing it and cleaning the area I measured the resistance between the power rails, to my surprise I measured about 0.6. Ohm.

Normally I would look for a short, but after rechecking the area around where  I removed the capacitor, including looking at the board under a USB microscope, and finding nothing I'm beginning to wonder if what I saw was the result of circuit elements conducting due to the 1V potential at the meter terminals.

The CPU ( which was removed ) runs on 1.6V according to the schematic I found.

My question, to anybody with experience in laptop repair, is whether this is plausible?

tautech:
Try another AC adapter to eliminate yours as the problem.

wraper:

--- Quote from: Bukurat on August 10, 2014, 10:29:48 am ---I found disassembly instructions on the 'net and disassembled the laptop so I could remove the capacitor. After removing it and cleaning the area I measured the resistance between the power rails, to my surprise I measured about 0.6. Ohm.

--- End quote ---
Did you remove CPU when measuring? They can measure very low on power rail. Also very strange about capacitor on CPU power causing reboot because of the AC adapter. It should not mater at all and if there is a short, it should not work from any power at all because power goes from the same step down converter anyway. There might be a fault somewhere between step down converter and AC adapter. There likely is some schematic with mosfets which switches step down converter power between battery and adapter.

G7PSK:
Is there a handshake requirement with the power supply, I know that many Dell laptops have this and I have had this problem with one in the past, the only easy fix was a new power supply.

tautech:

--- Quote from: G7PSK on August 10, 2014, 08:59:06 pm ---Is there a handshake requirement with the power supply, I know that many Dell laptops have this and I have had this problem with one in the past, the only easy fix was a new power supply.

--- End quote ---
The A300 has only a 2 wire DC connector.
Could it handshake?

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