The JK-EXT FC7.820.504

The JK-EXT FC7.820.504 (commonly Version V1.1) is the Extension Interface Board for the same marine/industrial telephone exchange system.

Continuing the sequence of boards you’ve identified, this specific card is the one that actually “talks” to the physical telephones throughout the ship or facility.

Technical Function: The “Extension” Board

While the CPU (.505) thinks and the Tone (.507) and DTMF (.506) boards handle signals, the JK-EXT does the heavy lifting of connecting the system to the user hardware:

• Port Management: It typically provides the interface for multiple analog telephone extensions (usually in groups of 8 or 16).

• Ringing Voltage: It generates the high-voltage signal required to make the physical telephone bells ring.

• Off-Hook Detection: It monitors the current on the line to detect when a handset is picked up.

• Voice Path: It provides the analog-to-digital (or vice versa) path for the actual voice conversation to enter the exchange’s switching matrix.

System Map Summary

If you are looking at a rack of these cards, here is how they work together:

Troubleshooting the JK-EXT

If you are troubleshooting a communication failure:

1. Partial Failure: If only a few phones are down, the fault is likely on this JK-EXT board or the wiring leading to it.

2. Hot-Swapping: These industrial boards are often not hot-swappable. Always power down the exchange before pulling or inserting the .504 card to avoid frying the line interface circuits.

3. Surge Damage: Because this board connects to long runs of copper wire throughout a vessel, it is the most common board to suffer from lightning or power surge damage.