Can not control with Repetier, but Cura ok.

I have two 3D printers. I used to control both with repetier, and they work well.
Recently, I upgraded firmware (marlin) for one of them. After that, the newly upgraded machine can not be controlled by Repetier,
the heatbed icon won't appear under manual control. For once, i succeeded, but only once. After that, no luck,
and LCD screen is totally dead there. But, I can control it with Cura even at this time and any time.
If it seems Repetier can not recognize a new printer.
The new printer is connected at COM3, while the other is COM4.
No matter i set COM3 or COM4 for the other, it can control it. Wired.
I think, it should only control it when it's COM4, but it still works at COM3, which is connected with a different machine.

Edited 1 time(s). Last edit at 06/08/2015 07:16AM by frankleng.

Shot in the dark, but have you double checked you serial link speeds? For a while I was defaulting to 115000, but got tired of always correcting it in the config file which defaulted to 250000. Perhaps it changed in the code you were using and Cura was already correctly configured or has some form of auto-detect that Repetier-Host is not using.

Turns out i should set "reset on connection" to DTR-high-low".