Offered in used, cleaned-and-tested condition with a one-year warranty, this DS3820MAUD1A1B is a Mark IV media access module assembled on a DS3800HMAC1G1F board. It is the hardware that puts a GE Speedtronic panel onto the system communication bus and manages how that panel accesses the shared network.

A complete Mark IV system-bus module (DS3820MAUD1A1B)

The DS3820MAUD is GE's media access unit for the Mark IV — a system bus module, in GE's own terms. It consists of an interface panel screwed onto the DS3800HMAC circuit board through nylon standoffs, presenting the connections and status indicators on the panel while the electronics sit on the board behind it. The module gives a panel two redundant routes onto the communication bus: Cable A on connectors JB and JC, and Cable B on connectors JD and JE. A link-controller connector (JA) and a power connector (JG) complete the interface. The board itself carries the timing crystals, transistors, and ten jumper switches that set how the module behaves on the bus.

Cable A, Cable B and the watchdog: first-line diagnostics

Before you decide this module has failed, let it show you what it knows. Three indicators on the panel — Cable A OK, Cable B OK, and Watch Dog Timer OK — report the state of the two communication paths and the board's own health. A practical sequence:

• Note which of the two Cable OK indicators are lit. A single dark cable indicator usually points to that cable run or the node at its far end, not to the module.
• If both cable indicators are dark, look upstream at the bus and the devices sharing it before assuming the module is at fault.
• Treat a Watch Dog Timer indicator that is not healthy as a prompt to verify the JG power feed and reseat the board, then re-observe.
• When fitting a replacement, copy the ten jumper-switch settings exactly; an incorrectly jumpered module can pass its own checks yet still refuse to join the bus.

These few observations regularly separate a genuine module failure from a cable or configuration issue.

Why the enclosed HMAC revision matters (1G1F)

This module is built on a DS3800HMAC1G1F board, and the board revision is not just a catalog detail. When you match a media access unit to an installation, both the module suffix (here 1A1B) and the enclosed board revision (1G1F) should be checked against what you are replacing, because a plant may standardize on a particular board build. If your existing unit carries a different HMAC revision — a 1G1E, for instance — tell us, and we will confirm whether it is an acceptable substitute. The GE Speedtronic Part Number Decoder shows how the module and board numbers are structured.

Where the MAU fits in the Mark IV network

The media access unit is one half of the Mark IV communication story. It arbitrates a panel's access to the system bus, while the DS3800HDRA line driver/receiver board handles the electrical driving and receiving of the signals that travel over it. Diagnosing a network problem often means looking at both. You will find related communication and control hardware in the GE Mark IV DS3800 Boards collection and across the broader GE Speedtronic Turbine Control Boards range.

Getting the right module quoted

For a 24-hour turnaround, please provide:

• The module part number and suffix (DS3820MAUD1A1B) and the HMAC board revision you require.
• A photo of the panel and board labels.
• The turbine and Mark IV panel the module belongs to.
• Quantity and how urgent the requirement is.

Request a Quote and we reply within a day. We ship worldwide DDP with duties handled, accept purchase orders from established accounts, and can quote the module, the bare HMAC board, or the companion HDRA together as needed.

General Information about the Product
Part Number	DS3820MAUD1A1B Mark IV DS3800
Description	DS3820MAUD1A1B by GE DS3820MAUD with DS3800HMAC1G1F Media Access Module
Condition	used Cleaned and Tested. With 1 Year Warranty.