How to Replace a Mercury Access Control Board: Step-by-Step Guide for EP1502, LP1502, and MP1502 Swaps

A Mercury board replacement is a two-part job: the physical swap and the software reconfiguration. The physical part takes 30 minutes if you’re organized. The software part depends on your platform and how well you documented the old board’s settings before it failed.

This guide walks through both parts. It applies to EP1502, LP1502, and MP1502 replacements across commonly used access-control platforms. Follow your platform vendor’s current administrator guide where its sequence differs.

Before You Order: What to Document

If the board hasn’t failed yet — or if it failed but you still have access to your access control software — document these settings before you pull the board.

• Controller IP address: Found in your access control software under hardware configuration
• MAC address of the old board: On the board label and in your software
• Reader formats: Wiegand 26-bit, 34-bit, OSDP, or other — check your reader configuration in the software
• Door assignments: Which doors (door names, numbers) are assigned to which reader ports on this controller
• Downstream panels: If you have RS-485 expansion panels connected, document which downstream panels connect to this head-end
• Network settings: Subnet mask, gateway, DNS — if you have a static IP on the board
• Event log snapshot: Export recent events if you need them for audit purposes before reconfiguration

If the board already failed and your software is the only place this information exists, pull it from the software now before you start the replacement process.

Step 1: Power Down and Label Everything

Before touching any wiring, power down the controller. This means both the AC power supply feeding the board and any backup battery. Do not rely on just unplugging the power supply — if there’s a battery backup in the enclosure, the board may still be live.

Label your wiring before you disconnect anything. Use tape flags or a label maker. For each terminal block on the existing board, label what’s connected: “Reader 1 D0,” “Reader 1 D1,” “Door 1 Lock,” “Door 1 REX,” “Door 1 Contact,” etc. This is the step most people skip and then regret. A photo of the wiring before disconnection is also worth taking.

If you have downstream RS-485 panels connected, label those connections too: which RS-485 A/B pair goes to which downstream panel.

Step 2: Disconnect and Remove the Old Board

With everything labeled and power off:

• Disconnect the reader wires from the terminal blocks (D0, D1, clock, data, GND, power)
• Disconnect the door lock output wires
• Disconnect the REX (request-to-exit) input wires
• Disconnect the door contact input wires
• Disconnect any auxiliary inputs/outputs
• Disconnect the RS-485 wires if you have downstream panels
• Disconnect the Ethernet cable
• Disconnect the power input from the power supply
• Remove the board from its mounting hardware

Set the old board aside. If it’s going back for a warranty claim, don’t discard it.

Step 3: Mount and Wire the New Board

Mount the new board in the same location as the old one. The MP1502, LP1502, and EP1502 use similar mounting configurations and will fit in the same enclosures in most cases.

Reconnect wiring in reverse order from disconnection, using your labels as a guide:

• Connect power input (verify voltage — MP1502 accepts 12-24V DC)
• Connect Ethernet (use the same cable and same IP assignment)
• Connect RS-485 downstream panels if applicable
• Connect reader wiring to the correct terminal blocks
• Connect door lock outputs
• Connect REX inputs
• Connect door contact inputs
• Connect any auxiliary inputs/outputs

Double-check reader wiring polarity. D0 and D1 (or clock and data) must be on the correct terminals. Reversed wiring won’t damage the board, but readers won’t communicate. OSDP readers use TX/RX rather than D0/D1 — verify your reader protocol and wire accordingly.

Step 4: Power On and Verify Network Connectivity

With wiring complete, power on the board. The MP1502 will run through its boot sequence (30–60 seconds). You should see network link lights on the Ethernet port.

Verify the board is accessible on your network before proceeding with software configuration. Follow the manufacturer’s current initialization procedure, locate the assigned address if DHCP is used, and apply the approved network settings for your site.

Step 5: Remove the Old Controller from Your Access Control Software

Platform procedure: In the hardware administration area, locate the failed controller and follow the vendor procedure to remove or replace it. Record every associated door and downstream panel first so they can be reassigned.

Avigilon Alta (ACM): In the ACM admin console, navigate to Physical Access > Controllers. Find the failed controller and delete it. Note which panels and doors were associated with it.

Lenel OnGuard: In System Administration, go to Access Control > Intelligent Controllers. Delete the old controller record. Note door and panel associations.

Step 6: Add the New Controller to Your Software

Platform procedure: Add a supported Mercury controller using its network and identity information, then follow the vendor workflow for firmware, downstream panels, and door reassignment.

Avigilon Alta (ACM): Add a new controller in Physical Access > Controllers. Select Mercury as the type, enter the IP, and save. ACM will connect to the board and bring it online. Reassign panels and doors.

Lenel OnGuard: In Intelligent Controllers, add a new controller record. Enter the IP and type. OnGuard will connect and register the board. Reassign doors and panels.

In all platforms: after the board is added and online, verify that the controller appears as connected (green/online status) before proceeding.

Step 7: Configure Reader Formats and Test

With the controller online and doors assigned, configure reader formats to match your badge system:

• Set reader 1 and reader 2 format (Wiegand 26-bit, 34-bit, OSDP, etc.) to match your cards
• Verify door contact state — open/closed should reflect correctly in the software
• Test REX — activate the request-to-exit device and confirm the door unlocks
• Test credential — present a known valid card and confirm access granted
• Test denial — present an invalid card and confirm access denied
• Test lock output — grant access via software and confirm the lock actuates
• Verify downstream panels if applicable — confirm RS-485 panels come back online

If readers aren’t communicating, verify D0/D1 wiring and reader format settings. If the lock isn’t actuating, verify the lock output wiring and the strike/magloc type setting (fail-safe vs fail-secure) in the door configuration.