If the plastic test sheet is not showing any dots or lines, please check the following: - Apply enough ultrasound gel between the cartridge and the test sheet. - Make sure the cartridge is fully flat against the sheet. - Confirm the machine is in READY/working mode and the energy level is not set too low. - Make sure you are using the correct test sheet thickness for the cartridge depth. If there are still no visible or tactile marks after testing correctly, please stop using the machine and contact **service@freyara.com** with your order number and a short video of the test. Our team can help check whether the cartridge is outputting normally.