Keurig k70 doesnt brew a full cup

Keurig K70 is taking water from the reservoir and send it to the inner water tank ok but when the tank is full and ready to brew, it only gives me 1/4 of a cup. It takes for ever to brew and very very slow water flow. I have descaled it 3 times, cleaned the needles and also removed the check valve on the top to see if it would make a difference after cleaning it, but it still not working. I have discovered that if i block the overflow outlet ( at the reservoir), the flow increases quite a bit but causes bubbles at the bottom of the reservoir where the water goes in. It seems that it could be a solenoid or a water pump but how to determine which one?. Also, i dont know how to open the Keurig K70 to have access to the inner parts ( solenoid). I hope you guys can help me.

Thanks in advance

Marc