PC Chips M571 (V3.2) undocumented voltage settings
--------------------------------------------------

The following schematic diagram shows the relevant section of the
on-board power supply (reverse engineered):

                                 6K81    11K5    30K1 Resistor
                             10K0    9K53    22K1      values

                             2V5 3V5 3V3 3V2 2V9 2V8  Jumper ID
    From  _____  _____
    Load  |    \/    |14     R88 R89 R90 R91 R92 R93  Circuit ref
     |    |          |--------|---|---|---|---|---|
     |   1| |\Error  | Vref  |-| |-| |-| |-| |-| |-|
Vout |----|-| \_Amp  | +5V   | | | | | | | | | | | |  Resistors
      ____|_| /      |       |-| |-| |-| |-| |-| |-|
    V |  2| |/       |        |   |   |   |   |   |
      |   |          |        |   O   O   O   O   O    Jumpers
      |   | KA7500B  |        |   O   O   O   O   O     JP6   
      |   |__________|        |   |   |   |   |   |
      |                       |---|---|---|---|---|
      |_______________________|
                              |
                        R79  |-|
                        10K2 | |
                             |-|
                              |
                             _|_




The following table lists the actual voltages for the various
jumper selections (0=no jumper, 1=jumper installed). It appears
that the design provides an 0.08V margin to allow for ripple and
ohmic losses.

Jumpers       nominal V     V - 0.08
3V5-2V8     (at regulator) (at CPU socket)

00000          2.53          2.45
OOOO1          2.88          2.8 
OOO1O          2.99          2.91 
OO1OO          3.28          3.2 
O1OOO          3.38          3.3 
1OOOO          3.58          3.5 


Q. How does one obtain a core voltage of 2.4V or 2.2V?
   ---------------------------------------------------

Core voltages less than 2.5V can be obtained by connecting a suitable
resistor in parallel with R79 as follows (2.2V shown):

                                 6K81    11K5        30K1 Resistor
                             10K0    9K53    22K1         values

                             2V5 3V5 3V3 3V2 2V9 2V8  Jumper ID
    From  _____  _____
    Load  |    \/    |14     R88 R89 R90 R91 R92 R93  Circuit ref
     |    |          |--------|---|---|---|---|---|
     |   1| |\Error  | Vref  |-| |-| |-| |-| |-| |-|
Vout |----|-| \_Amp  | +5V   | | | | | | | | | | | |  Resistors
      ____|_| /      |       |-| |-| |-| |-| |-| |-|
    V |  2| |/       |        |   |   |   |   |   |
      |   |          |        |   O   O   O   O   O    Jumpers
      |   | KA7500B  |        |   O   O   O   O   O--|  JP6
      |   |__________|        |   |   |   |   |   |  |
      |                       |---|---|---|---|---|  |
      |_______________________|                      |
                              |                      |
                        R79  |-|                    |-|
                        10K2 | |                    | | 39K
                             |-|                    |-|
                              |                      |
                             _|_                    _|_



In the above case there is effectively a 39K resistor in parallel with
R79. All other jumpers are removed. The ground side of the 39K resistor
can be connected to a nearby ground pin such as pin 3 of the speaker 
connector (J3), pin 5 of the keylock connector (J3), or pin 3 of the 
fan power connector (J2). The nominal output of the regulator is 2.23V.

For 2.3V (nominal 2.33V), a 62K resistor should be used.
For 2.4V (nominal 2.43V), a 120K resistor should be used.

The required resistance can be computed using the formula:

 R = 102 * Vcore / (51- 20.2 * Vcore)

Conversely, a resistance R will produce the following core voltage:

 Vcore = 51 * R / (102 + 20.2 * R)