Genuine LiftMaster K79-40370 battery charge control board — the main control and charging board for the SL920 and SL930 DC slide gate operators. It runs the operator and manages the charge to the battery bank; on both models the board, the K74-40084 bridge rectifier and the transformer form the charging chain, and a board that no longer charges is the usual reason it is replaced.
Charging faults are a chain, not one part. Batteries that never reach full charge can be the batteries themselves, the rectifier, the transformer or this board. Check the rectifier output and the transformer before condemning the board — the rectifier is a fraction of the cost.
Specifications
| Part number | K79-40370 |
|---|---|
| LiftMaster description | Control Board, Battery Charge — SL920 / SL930 |
| Fits | LiftMaster SL920, SL930 (70 V DC motor, battery-backed) |
| Condition | Genuine LiftMaster OEM, new |
Which operators use it
| Operator | Parts page |
|---|---|
| SL920 slide gate operator | SL920 parts |
| SL930 slide gate operator | SL930 parts |
Not the SL505 / SW425 board. The SL930 shares a few service kits with those operators but runs a 70 V DC motor on its own platform; their control boards are different parts.
Parts often replaced with it
K74-40084 bridge rectifier · see the model page for the transformer, batteries and alarm
Is the board actually the problem?
The logic board is the most over-ordered part on a commercial operator. Work down this list before you buy:
| Symptom | Check first |
|---|---|
| Batteries never reach full charge, gate slows or quits under load | Batteries, then the rectifier, then the transformer, then this board |
| Breaker trips repeatedly | Rectifier or transformer shorted, or a motor fault — before the board |
| Piezo alarm sounding, gate stopped | A board fault or a low-battery alarm — check charge voltage first |
| Dead after a storm | This board — and fit surge protection with it |
After fitting
Check the charge voltage at the batteries after fitting, set the limits and re-test the entrapment protection.
Fit surge protection when you fit the board. Lightning and utility surges are the most common reason a commercial operator board is replaced, and a new board on the same unprotected supply is at the same risk. The MOV kit on the electrical box is the first line; a proper surge arrester on the supply is the second.
Related
SL920 parts · SL930 parts · all LiftMaster gate operator parts
Not sure which board you need? Send a photo of the number printed on your existing board to parts@gatehousesupplies.com or call 866-965-5599. We would rather confirm it than have you fit the wrong board.
