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Old 09-13-2012, 09:03 PM   #1
nubie
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Default Toshiba C655D No AC power, will run off battery.

When I plug in the AC adaptor it is thoroughly dead, not even a blink. Power traces OK through the onboard fuse.

I soldered wires to the battery socket and can trick it into startup with a battery installed, then it will continue to run with a 12v power brick on the battery lines. I don't have a battery because it will go back to the customer.

I am planning to use this as an embedded type system or off of lead acid battery. I already put a replacement motherboard in the laptop for the customer.

Fuses check out OK, I am guessing this suffered some kind of surge because the laptop was given to me with a Targus power brick (correct 19v).

Just interested in finding the faulty component and bypassing it so it will run off the wall as a slimline PC.

I have the data sheet for the power IC, it is a TPS51123.

EDIT: After searching for C655 only I find this: http://www.badcaps.net/forum/showthread.php?t=21949 Maybe it will help.

Last edited by nubie; 09-13-2012 at 09:06 PM..
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Old 09-13-2012, 10:07 PM   #2
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Default Re: Toshiba C655D No AC power, will run off battery.

Check the two MOSFETs that are used to switch and reverse-block between the battery and the AC. I had a similar fault and it turned out the MOSFET was dead.
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Old 09-14-2012, 12:26 AM   #3
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Default Re: Toshiba C655D No AC power, will run off battery.

Quote:
Originally Posted by inflex View Post
Check the two MOSFETs that are used to switch and reverse-block between the battery and the AC. I had a similar fault and it turned out the MOSFET was dead.
Thanks for the reply,

It seems this circuit is much smarter than I am, I just want to bypass the charging circuit and run it off the wall, no dice.

I did check one of the N4800LS MOSFETS on the input (Q6002) and it is indeed shorted. I removed it and the same symptoms. Any ideas what I could replace it with? Looking on Digi-Key shows $0.46, or $10 after handling. Looking to spend maybe $3 tops.

I have a pile of circuit boards here, will be looking at them for harvesting (Xbox360, CD drives, etc.).
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Old 09-14-2012, 12:42 AM   #4
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Default Re: Toshiba C655D No AC power, will run off battery.

Forgot to mention, with Q6002 completely removed it still has the same symptoms, runs fine off of a charged battery, dead when AC is plugged in.

Edit: ordered AO4422, any reason that won't work?

Last edited by nubie; 09-14-2012 at 12:53 AM..
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Old 09-14-2012, 12:49 AM   #5
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Default Re: Toshiba C655D No AC power, will run off battery.

Replace it with anything of superior spec, I had a bunch of FDS8866's around and used those. Get the datasheet for the N4800 and look for Rds(on) and what current the body-diode can cope with. Qc(total) is also important for some (but not a major thing for the select/blocking MOSFETs).
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Old 09-14-2012, 01:01 AM   #6
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Default Re: Toshiba C655D No AC power, will run off battery.

Quote:
Originally Posted by inflex View Post
Replace it with anything of superior spec, I had a bunch of FDS8866's around and used those. Get the datasheet for the N4800 and look for Rds(on) and what current the body-diode can cope with. Qc(total) is also important for some (but not a major thing for the select/blocking MOSFETs).
The old one is rated 14m Ohm @10v and 20 m Ohm @4.5v 8.6 amps.

The AO4422 is rated 15m Ohm and 24m Ohm. 11 amps dissipated

I am hoping that is close enough for a bodge fix.
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Old 09-14-2012, 02:27 AM   #7
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Default Re: Toshiba C655D No AC power, will run off battery.

It'll work.
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Old 09-14-2012, 02:32 AM   #8
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Default Re: Toshiba C655D No AC power, will run off battery.

Yep, that's pretty damned close enough I usually replace them with 3~7mOhm units only to keep the temperature down a bit more, but it's only me being pedantic.
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Old 09-22-2012, 07:16 PM   #9
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Default Re: Toshiba C655D No AC power, will run off battery.

Well, the chip came and I installed it. Success

I don't have any RAM, but the lights come on, and a beeping from the speaker, so I will call it good. Thanks everyone, and especially inflex for solving this problem before me.
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Old 12-08-2012, 06:35 PM   #10
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Default Re: Toshiba C655D No AC power, will run off battery.

I have just repaired a C650 with the same fault.
The laptop would only flash a green LED while charger powered and do nothing else.
The N4800LS MOSFET seems to be adequately rated.
Im worried about the cause. I dont have the original charger to test if it has a problem.
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Old 12-31-2012, 10:12 PM   #11
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Default Re: Toshiba C655D No AC power, will run off battery.

C655 here in my posession is doing this as well, but I"m not getting battery from either the AC jack or the battery at all. nothing happens.

I had this happen to a motherboard I cleaned the corrosion off of, and then again to one I got off eBay to replace it which was otherwise working fine.

so for it to happen to both in one shot, I'd say the MOSFETs or TI controller on these boards are seemingly becoming a common problem?
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Old 01-21-2013, 01:41 PM   #12
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Default Re: Toshiba C655D No AC power, will run off battery.

had similar issue with this model worked on 2 tota,,l one was bad mosfet and the other positive wire broke inside the dc jack had to pop off little cover on backside dc jack and re soldier it. solved the problem....
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Old 03-21-2013, 04:15 PM   #13
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Default Re: Toshiba C655D No AC power, will run off battery.

I replaced the MOSFET on one of these laptops with the bad Q6002, and now it will detect and boot from the AC adapter.

However, it detects the battery, but says (0%, charging) for hours on end, but doesn't actually charge the battery. The battery is dead from before when it would only work off the batt. The battery is not defective as I can charge it in another device.

Is there another MOSFET I should be checking maybe more than one shorted out?
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Old 03-22-2013, 08:04 PM   #14
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Default Re: Toshiba C655D No AC power, will run off battery.

Quote:
Originally Posted by evanesce View Post
I replaced the MOSFET on one of these laptops with the bad Q6002, and now it will detect and boot from the AC adapter.

However, it detects the battery, but says (0%, charging) for hours on end, but doesn't actually charge the battery. The battery is dead from before when it would only work off the batt. The battery is not defective as I can charge it in another device.

Is there another MOSFET I should be checking maybe more than one shorted out?
probably the other one next to it....
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Old 02-03-2014, 03:17 PM   #15
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Default Re: Toshiba C655D No AC power, will run off battery.

hi all , just to update ya , i installed the 2 new mofsets and shes back up and running . had to change 002 and 003
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