Custom Riser Card for MB770 Platform

MB770 motherboard is only PCI 2.1 compliant and therefore doesn't provide 3.3VSB (3.3 V stand-by voltage) on pin A14 of the PCI bus connector. This voltage is is supplied to the core of CM2 and is used to turn the main power on/off. Furthermore, even the wake-on LAN (WOL) connector on the motherboard doesn't provide stand-by voltage (and on most motherboards the WOL connector is not even installed).

One solution to this problem was to create a custom riser card shown in figure 1 which has a separate feed for stand-by voltage directly from the power supply, voltage regulator for 5 to 3.3 V conversion and feeds 3.3V to the CM2 card on PCI connector A14.

Standby voltage feed

CM2 stand-by voltage is provided with the separate wire that is attached directly to the +5VSB wire of the ATX power supply with the self-tapping connector (MOLEX ​Multi-Lock Insulation Displacement Connector (IDC) ) show on figure 2.

The purple wire on the ATX power supply connector is fed through the slit opening on the IDC while the red wire from the riser card is fed into the second hole on the clip and the taping header is gently squeezed into position and locked with the cover.

20 Pin ATX Connector

Pin	Name		Color	Description
1	3.3V		Orange	+3.3 VDC
2	3.3V		Orange	+3.3 VDC
3	COM		Black	Ground
4	5V		Red	+5 VDC
5	COM		Black	Ground
6	5V		Red	+5 VDC
7	COM		Black	Ground
8	PWR_OK		Gray	Power Ok (+5V & +3.3V is ok)
9	5VSB		Purple	+5 VDC Standby Voltage (max 10mA)
10	12V		Yellow	+12 VDC
11	3.3V		Orange	+3.3 VDC
12	-12V		Blue	-12 VDC
13	COM		Black	Ground
14	/PS_ON		Green	Power Supply On (active low)
15	COM		Black	Ground
16	COM		Black	Ground
17	COM		Black	Ground
18	-5V		White	-5 VDC
19	5V		Red	+5 VDC
20	5V		Red	+5 VDC

Installation

The assembled node with custom raiser and CM2 card is shown in Figure 3. The +5VSB clamp and feeder wire are pulled out of the box just to emphasize the setup.