Find the problem.

Ok, ive got a v1.2 motherboard, assembled as per wki for use with the ATX power header. It does not turn on unless i am pressing on the pin for the green wire (power on) on the back (with one of the ground wires. I think this means that ive got a loose connection somewhere, where could it be, any help is greatly appreciated. p.s. i have no real knoledge of electronics, probably a bit ambitious trying to build this.

... have you soldered the 30-Ohm-resistor?

The ATX-PS needs a ballast-resistor or it won't start ...

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Viktor
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Yes, it does heat up when i trigger the power to run via jumpering the pwer wire to the neuteral. Also not being detected when i try and program the bootloader, though that may be a problem with my usbtinyisp.

In general, its been said that 90% of any electronics troubleshooting comes from shorts, cold joint, solder points not done, etc.
If you soldered yourself, some parts have pins that play as vias (connecting top and bottom), check those for a start. Identify if there is anything not done, maybe meter routes top to bottom to make sure.

Check if the changes mentioned here [www.reprap.org] are done properly. I think important are link near the um232r header and the bridge in the atx spot. That small condenser and the 3.3 volt regulator i think (not sure) seem to be only used by the smd card, which in its turn is not used, so you may leave those aside if u want to.

As far as i can say in reprap configuration the power button is used for ... nothing, you could desolder it. The MB power comes from the USB. Power button lights up when u connect the usb connector. If it doesnt, you probably havent made those changes or have a interrupt somewhere. External power supply just goes to extruder and stepper drivers.

About programing, remember the jumper there.

The usbtiny is probably ok. If you dont use it as dongle, you can remove 2 resistors and put bridges there - details on its support page. what i did i actually put bridges on top of the resistors, because if i would take them off, i would certainly need them and forget where i stored them. I get that alot.

You can use usbtiny to program the mb and extruder directly, without the need for a bootloader, but you need to make a change in a .txt file that mentions the preferences for arduino, normally in docs and settings\user\app data\adruino, change upload.using=bootloader to upload.using=usbtinyisp This is mentioned somewhere in adruino.cc.

Remember even when you program it and works ok, that doesnt mean the pcb is 100 done, just that the link between programmer and its routes to the 644 works, you still could have interrupts to stepper headers, etc.

Good Luck!

The way i have my mobo set up its the makerbot way so i can run everything off a power supply. I have checked the solder conections and i cannot find any problems, i have now got it switching on and off by changing R18 for a 1.5K resistor instead of a 10K resistor so the power supply triggers. The chip is still not being detected by my comp when i try to bootload it (unisn a usbtinyisp), each time getting an rc=1 intialisation failiure.