PCB MK1 + power supply not enough power?

Here I attached a picture with my connection scheme. As a "beginer" on reprap prusa building I really don't know how bad is the vales of the voltage that I'm getting.

Following the scheme, at the "point A". and just connecting the power supply only to the PCB Ramp's input plug, and with a multimeter, I get 11.87V.

After turning on the PCB on Pronterface, at the same point and with a 24ºC (just turned on), I get 10.60V.
If I measure at the "point C", I get -10.24V.
If I measure at the "point D", I get -10.08V.

I wait 10 minutes or something like that for a warming up and getting 70ºC, I measured the same points again, getting:

Point A: 10.67V
Point C: -10.31V
Point D: -10.11V.

Also said that the wires between the PSU and the RAMP get really hot. I don't know if that's so normal.

As pointed out in another thread you need to wire about 4 black and 4 yellow wires from the power supply. The ratings on PC power supplies are mainly factious and the wire gauge is not enough to draw all the current from one source. Even with 4 wires I found they got warm.

The connections to the bed need to be thick 13A mains cable, or lots of thinner wires in parallel.

You need to have a load resistor on the 5V rail. That will make a big difference, with 10V you only have 70% of the power you should have.

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[www.hydraraptor.blogspot.com]

How should I wire those four wires that you say? I mean from my power supply comes up 2 pair of 12V (2 rais, what means two pair of yellow and black wires). Do you mean I change the current pairs and add another 2 pair of wires to those ones?

I used two yellow and black pairs from the 4 pin CPU connector and two more from the disc drive connectors and wired them all together for my heated bed.

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[www.hydraraptor.blogspot.com]

I currently use 14 gauge wires for the HBP, I take 2 of the yellows from the molex (14awg with tinning fits snug in there) and 2 wires from the negative of HBP to the RAMPS D8 negative terminal.

If your PSU has 2 rails make sure the RAMPS and HBP are on seperate rails with 10A per rail. Check your PSUs wires, sometimes manufactures use a color banded yellow wire for 12V1 and a solid yellow wire for 12V2 (or vise versa though it doesnt matter which you use to power ramps or HBP). If yours doesnt have the color coded wires most are seperate via CPU power and "the rest of computer power". which is usually, 4 pin square CPU 12V connector or 8pin (4x2 pin) CPU 12V connector for 12V1 and everything else will be 12V2.

Edited 2 time(s). Last edit at 12/21/2011 07:08PM by ECSuyu.

I followed the Nophead advice and connect the three pairs of wires and it works fine. I also had a thermistor problem, wich was reading wrong temperatures, under the real one, I changed it by an Epcos 100k and where the old one was reading 70ºC the new one measure 96ºC. Anyway, I just think it still reads under the real, so I'll check it with a infrared temperature tool (when I get it from post). My power supply was 12V 20A, what maybe it would be enough (I'm getting really good quality printings and no wrapping anywhere or any bending) but I ordered a 12V 30A PSU and connect both of them, the old PSU will work much more "relaxed".