I have a new 12" MakerFarm printer (RUMBA with bed heater relay) and found that when the bed heater is on, the print quality goes down. Have checked the power supply, cable size, etc. The moment the bed heater turn on the extrusion goes thinner and does not lay down well. Input voltage is 12.32, drops to 12.28 when the heater is on. I'm thinking the electronics (RUMBA) has a problem, but looking for advice before I buy a new board.