heatbed going above target temperature

I ran the M303 command to fine-tune PID parameters for the hotend and heatbed. The hotend seems to be doing fine. My heatbed is set to 85C. It keeps going up from that point. The recent print test print I did ended up at 104C. What would cause it to continually go higher? IIt's a silicone heatbed attached to a 3mm aluminum plate. The temperature rises as the printing starts. I'm using Repetier .92 firmware.

Edited 1 time(s). Last edit at 02/29/2016 02:04AM by mlaustin66.

In case anyone else has this problem, I found the solution on another forum. Apparently the resisters were touching that caused some kind of short. Here is the picture from the other forum.

hi Mlaustin
not to pick but what you calling a resistor is actually a MOSFET in the picture. I notice you used black and red wires but the black connected the positive output,

unlike the Hotend I dont think its critical to have PID running on the Bed.

Edited 1 time(s). Last edit at 03/11/2016 01:19AM by jinx.

PID is already baked into the firmware, costs nothing to use, and will prevent certain types of print defects. Use it. It works.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]