Technical Solution for Mitsubishi Elevator VFGLC System "BKS" Error

一、Symptom & Root Cause

• Symptom: "BKS" displayed on hall panel, elevator locked, typically triggered during automatic self-check after 30 mins of inactivity.

• Root Cause:

  1. Insufficient static brake torque (Threshold: ≥180N·m).

  2. Unilateral brake failure (mechanical jamming or electrical fault).

二、Step-by-Step Troubleshooting

2.1 Static Torque Test Mode

Step 1: PrepAration

1. Safety Precautions:

   • Cut off main power, hang "Maintenance Mode" sign.

   • Move the elevator to top landing zone with no load, ensure car is stationary.

2. Tools Required:

   • LHS-420X control board, HIP hand-held terminal (connected to COP port).

Step 2: Enable Test Mode

1. Operate LHS-420X board:

   • Rotary switches: SET1=0, SET0=1 .

   • Toggle SW1△/▽ to ▽ side (downward arrow).

2. Reboot System: Briefly press CP (Control Power) switch.

Step 3: Low-speed Upward Test

1. Switch to low-speed mode (via car top or control panel).

2. Press RUN on HIP terminal to maintain low-speed upward movement.

   • Key Note: Brake remains closed, system gradually increases torque.

Step 4: Torque Validation

1. Monitor hall display:

   • Normal: Numerical value ≥180 (Unit: N·m).

   • Abnormal: If <180, stop test immediately and proceed to unilateral brake test.

2.2 Unilateral Brake Test

Step 1: Exit Static Torque Mode

1. LHS-420X settings:

   • SET1=0, SET0=8, keep SW1▽ downward.

Step 2: Enable Unilateral Control

1. Set LHS-420X monitor switches:

   • MON1=0, MON0=3 .

Step 3: Manual Brake Release

1. Release Brake 1:

   • Press RUN + UP on HIP terminal, hall display shows "B".

   • Judgment: Car speed ≤2m/min is normal; "E" indicates failure.

2. Release Brake 2:

   • Press RUN + DN, repeat the above process.

Step 4: Fault Handling

1. If "E" Displayed:

   • Stop operation immediately, cut off power.

   • Remove brake cover and check:

     • Brake spring alignment with marked line.

     • Brake surface contamination (clean with ethanol).

     • Lining thickness ≥2/3 of original.

三、Safety 

• Safety Warnings (Red/Bold):
  🔴 NEVER adjust brakes without cutting main power!
  🔴 Unilateral test requires two technicians: one operates HIP, another monitors the car.

四、Appendix

Figure 1: LHS-420X Switch Layout

Figure 2: HIP Terminal Buttons

Figure 3: BK electrical drawings