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13.8 vdc from computer power supply




 
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Author Topic: 13.8 vdc from computer power supply  (Read 492 times)
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wa2tak
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« on: February 16, 2023, 02:45:52 PM »

I Goggled lots of stuff on this topic.
Most are unhelpful ...not simple.
"Best" one is:
https://www.youtube.com/watch?v=iQDJ9SspAPs

WHAT A JOB THIS WAS!!!!

The BIG 'problem' is that there are MANY makes/models control chips in these units...
...and just about no info on them!
And..your lucky is you can find the circuit diagram and chip info for that PS!

Most computer supplies are type "ATX".
All of them supply 5V, 3.3v, and the important one = 12V.

The process is changing/removing resistors that make up the voltage DIVIDER circuit in the 5V and 12V circuit...and MAINTAIN the ( usually ) 2.5V 'control' voltage PIN that monitors all voltages...and...'automatic' OFF if things go wrong in the PS.
The chip control pin is the one common for both 5V and 12V output.

The object is to get 13.8 from that 12 output wire by removing certain resistors in both lines...and FINDING the new value of the resistor in the 12V line..ROTS OF RUCK.

The voltage/wire code is 'standard'
The 12 is yellow.
The 5 is red.
Ground is always black.

My chip is 2003.
The 12 volt is yellow; 5 is red.

The resistors that need "attention" are the ones in series with 5V line output...
and the MAIN resistor - getting the NEW value - the one in series on the 12V line.
And...most often one of 2 resistors in parallel in these 2 lines needs to go.

Four resistors using hit & miss approach.

Not being a circuit designer...and using my soldering iron...I did a time consuming hit or miss approach
and, knowing that the MAIN resistor needed a different value...hooked a variable pot.

Turned out...I removed R39 ONLY...one of the parallel resistors.
I removed R60 ( the MAIN one ) in the 12 V line...that needs the new value.

By shear luck I found that I needed 220K for the MAIN in place of the 121K that was there.

ALL THE WHILE YOU PUT A VOLTMETER TO THE 12V output...+ to yellow  - to black.

The 'easy' part is that the fan does not work...and NO voltage... if your wrong playing around with those - in my case - 4 resistors.

Also...learned the hard way...Nothing happened...did NOT ground the metal 'chassis' to the black wire!!

This was one heck of a time consuming job..."knowing nothing about anything"!!!

But got my 13.7 volts.

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