I have been involved in electronic repair now for many years & I am still amazed however at the stupidity/cleverness of engineers when it comes to the use of conductive glue and "sweaty" wedges in their devices. Their use has been known to cause failure in electronic devices for over a decade. So the use of both these products in the one device is either downright dumb or planned obsolescence at it's most sinister...
I first came across conductive glue in my vcr (link provided for today's kiddies) repair days. When it is first applied in the factory this stuff is not conductive. As it ages (gets past warranty), especially if it is heated, this glue turns from a pale yellow to a deep brown. In the brown state it becomes conductive in the order of 1 Mega Ohm of resistance. Quite high, but enough to pull digital inputs to another state, or short out switch mode power supplies. The Billion 7404V uses this glue in and around the power inductors, to prevent magnetostriction. It is also used to glue relays to the board and to prevent movement to the WiFi board and connectors.
The Billion 7404V also uses "sweaty" wedges. These are pieces of rubber used to support things. They sweat with age (past warranty!!) and heat and this liquid can short things out or corrode copper. I came across sweaty wedges when I was involved in CRT (again link provided for today's kiddies)TV repair. The wedges were used to support the deflection yoke. On occasion they were of the sweaty variety. When they sweated they caused the yoke to corrode, and you would either not get any Vertical deflection of the electron beam or the High voltage section of the TV would fail with the Horizontal deflection.
The above two causes of failure are manufacturing faults, plain and simple, do with that information as you please. My unit was out of warranty and I could not initially afford the time to do a repair, so I purchased a new router, with the hope of using this one to extend my wireless range later if I repaired it.
What follows is my solution to both problems, remove the glue and in this case dry and cover the wedge.
Step 1: Get Some Tools
Step 2: Remove the Glue
To get started, remove each RF cable press connector by prising it away from the board. Then unclip the board from it's holder. Clean the WiFi board up and then move onto the Main board by the back panel and sliding it out the back.
Step 3: Sop Up the Sweat
Step 4: Put Is Back Together
Put on the lid, screw it back together and you should hopefully be done!!