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386 laptop inverter repair help

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First post, by MAZter

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The 386 laptop inverter has failed, what could be the reason, where and what can be measured to understand which part to replace?

Hitachi INVC136

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I temporarily replaced it with an inverter from 286 notebook, Elevam EHI-12040, but I would like to repair original one

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Doom is what you want (c) MAZter

Reply 1 of 2, by DAVE86

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First check the fuse with a multimeter. F1 position. Use low resistance range or diode/beeper mode. If it reads open circuit then there has been some sort of overcurrent and changing it might solve the issue.
However. The electrolythic capacitor C1 might have gone dry or worse leaked. From the photos it's hard to tell that the discoloration is wet electrolyte or just flux residue. If electrolyte has flown under the IC1 MT494FP controller and other parts then the repair gets significantly harder since the Q3, Q4 and other components might have failed too. I've had the 494 pwm controller fail in a similar inverter and it killed the power transistors too. Worst case the TF1 impulse transformer has broken windings but let's not go that far yet.
My bet would be the leaky capacitor. That will involve dissasembly and very through cleaning first.

Reply 2 of 2, by MAZter

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DAVE86 wrote on 2025-01-20, 13:10:

My bet would be the leaky capacitor. That will involve dissasembly and very through cleaning first.

Thanks! At least I know first steps now.

Doom is what you want (c) MAZter

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