Thursday, December 29, 2011

Toshiba L455D - Powers On Then Off

Toshiba L455D Blink On then Off Light.
Power light functions normally. Charge light functions normally.
Does not run. Does not post.

Turns on then shuts off. The unit powers on then after a few seconds- shuts off.

This is was caused by a shorted MOSFET PQ10 that exhibited a full short 0Ω Since they were in a pair formation, both were replaced so the current level would be balanced.  The cost is so low, that it was not a consideration. Two AO4466 replaced with two AO4468 mosfets which were available.  AO4468 is out of production, but were found on an HP DV6000 near the Maxim [MAX8734/PU10] quad output power distribution chip.             (PQ31/PQ32 on DV6k)

The coil PL3 was cracked in half, was not exactly sure if the coil would be defective, but the nature of coils is to push current within the electromagnetic field, so if the field is open the electrons may not go forward, tools did not allow the ability to verify. So it was replaced. 

(When in doubt, replace)

Please No Questions regarding this repair- They won't be answered
It was simply found by finding the shorted MOSFET. This is only a reporting blog for other to have an idea where to find the problem, not to fix it for them.  Use logic in following the electrical path.  You can not learn if you are always shown the answers.

Note: No Video issues on this model is caused by the nVidia GPU, not this area. This is the power-in section. Do not reflow the whole GPU at one time, because it not anchored by epoxy. Do half, allow time to cool, then other half.


  1. hello sir,sorry for asking you question..but my benq joybook r43 have similar symptom,as soon as i released the power button the power just off.can you please give me suggestion which part should i check...please,and sorry again for asking you with the question.

  2. Adam, I have no experience with Benq products. Though the symptoms may be the same, the design is different. The information posted is not general, it is specific for the model described. Sorry, but I cannot diagnose and troubleshoot via the Internet.

  3. Anyway thanks for your replay,i've really admired all your works,i hope you will always updating your blog and always be the best Laptop Dr.About my problem,i'm thinking of replacing the max 8770 ic because it is the ic which distribute the power to the fan and cpu and the Thermistor that placed at the shtdwn pin has blown.I think it indicate that overheat possibility.Then again,thank you very much for replay.You my idol.Love your works :)


I cannot repair laptops for you via the internet, I can only answer questions related to posts. This is because I have not had experience on every motherboard that is out there. Bear with me.

If you do need it repaired. Contact me for quote (US/CDN Only)

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