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)
This page was last modified on 17 July 2002