I have a HG 659 router and an Arris NBN modem. Since we had this connected (3 months), the HG 659 drops out at least a dozen times a day. I powercycle and the signal is restored. All lights on the modem remain green, but the "internet" and "wan" lights on the router go out when the dropouts happen.
It's incredibly frustrating, and I'd love a solution.
I have noticed some users are connecting the TPG HG659 with the old ADSL power adaptor 12VDC 1A!!
The device will run fine for few months or years damaging the modem and creating drops on the service.
The correct power adaptor 12VDC 2A
After that, You can tried with at spare modem or loan one. Just ask to TPG technical support for more assistance