Heated bed problem

Hi , I've got an 550W ATX PC power supply and I changed it like this: [reprap.org]. If I turn on the heated bed on RAMPS 1.4 the PSU is turn off, and this is the same problem if I connect it directly to the PSU. My question is what is the reason, why is this happens? The PSU can provide 22A on the 12V rail. Everything works fine just the heated bed turns off the PSU. I don't know what need to do, i hope anyone offer some advice?

Read this section: [reprap.org]

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[www.hydraraptor.blogspot.com]

If you have a multimeter, use the ohm test to see if you have a short on your heatbed, i.e. reading less than 1 ohm.
That would deffo upset your PSU.

I fried a High Side Driver (VNO5) that I was trying and experienced a similar problem.... So if you are using a SSR, FET, HSD, LSD, also check the in and out pins with a meter (whilst the control board is off) to see if your devices is fried (internally shorted), if it is you will get a very low score, again less than an ohm. If its a HSD check connection between output pin and ground, it should be open circuit, if not...its dead. Same with LSD but between output and +v rail, disconnect heater first.

I measured 0,4ohm on the heated bed, what could cause this, bad soldering or the bed is faulty somewhere? How can i check it?

I already solder one of the red wires to the 10W resistor and the other end a black wire in the PSU.

Hi I know what was the problem, I have an MK2a heated bed and I solder the wires to the connector places on the other sides too, so I made an short circuit. Thank guys for helping

That 0.4r reading sounds like a dead short somewhere, the 0.4 is the impedence of your test leads.
Are your resistors wired in a chain Like this (psu +)------(res)-----(res)-----(res)-----(res)-----(psu -).??
If so Your readings should be Ohm value x number of resistors. if not then you may have shorted against the aluminium bed.(assumuming you have 4 resistors screwed to an aluminium bed)
hope that helps, give it a good viisual inspection and double check your wiring (whole system) for mistakes.

OK. That last post came a bit too late.