Recently I was trying to program a new remote for my Steel-Line RD1T system ( a rebranded Boss – BRD1 )
When I set my door to program mode , I wasn’t getting the flashing LED described. Sometimes when powering on the device the LED is faint and needs to be recycled which signals some kind of transistor failure , however an inspection of the circuit board showed no faults.
I tried to email Steel line about the information of circuit diagrams , however was ignored.
I found a Sonoff RF 3 switch could be purchased for less than 15 $ and take new remotes as well as well as connecting to Wifi so you could use your phone as the remote.
This guy did a great tutorial on the RF2 switch , the RF3 is a bit smaller however the same modification could be used. I use the pinouts on the on and off switch of the garage unit ( as too old to have its own inputs )