Modification of IBM notebook power supply
Identify the voltage divider:
First I opened the case and looked for the feedback circuit and voltage divider.
Then, I tried to locate the two resistors that are responsible for setting the output voltage.
The stabilization of the output voltage can be archived in the same way as TL431.
TL431 will be used in chip switching mode supplies and you can find many documents about its functionality in internet.
The location these two resistors can be found near the opt-coupler.
Measure the voltage at the opt-coupler was about 1.9V
On the left side of the board I found a tiny circuit board, which is shown in the picture. I assume its functionality is the same as TL431.Additionally, on the tiny broad I found the resistor R62 with 1.9 K in series to RX51.
I soldered parallel to R62 (1.9K) a new 6.8K resistor.
The result was 1.4K and gave me an output of 11.8 Volt and max 3.4 Amper
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