Modem/Router combo keeps restarting

[roknrollaw]

I have a Arris SBG6782-AC (modem/router combo). The signal isn't quite making it to the living room TV so streaming suffers. To fix this issue, I figured I would add an access point to that end of the house. (I'm unable to get a wire all the way to the TV so an AP nearby was the best I could do.) I thought I'd try to re-use a similar modem/router combo I have on hand - an Arris  SBG6700-AC - and just turn it into an access point. To do that, I just disabled DHCP on the 6700 (and connected it to one of the 6782's LAN ports). I went the route of assigning both units the same SSID/wifi password.

 

After adding the 6700, I am seeing the 6782 reboot multiple times a day. Any ideas on what would cause this? How would you troubleshoot something like that?

 

Here's what I've tried so far without noticeable affect:

1. Using different SSID's for the two units.

2. Reducing the wifi output power on both units from 100% to 75%.