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GCA85 LocoBuffer with 15V 3A Power supply


By Peter Giling

The assembled board


GCA85 is mostly an exact copy of the LocoBuffer (Without USB) of John Jabour.
It is added to provide an easy way to connect GCA50 units together, and also provides a 15 Volt 3 Amp power supply for the LocoIO.


Always use dedicated transformer for GCA85 (16V-18V mimimum 50 VA), which is not used for anything else.
Also do NOT connect brown connection (like on Marklin transformers) to any connection of GCA85 or anywhere else in the Loconet®!
Connecting so could cause serious damage to Loco-I/O modules and PC!
This of course unless some connections are specifically indicated.
Copying and building this unit is very much encouraged.
The responsibility of doing so, is ALWAYS totally for the user himself.
It is working satisfying on many railroad tracks.
I have given all efforts to make this unit safe, but even so, no responsibility can be taken for failures of any kind.

Port settings

Baudrate 57600/19200
Handshake RTS/CTS
Data bits 8
Stop bits 1
Parity none

Baudrate is selectable with on-board dip-switch 2.

Supply Power

GCA85 needs 14-18 V ac or 16-20 V dc 50 VA.
The best option is a dedicated transformer / DC supply of minimal 50 VA, for full function.
Less power is possible, but be sure to adapt Fuse F1 to that situation.
Any questions, ask Peter

Power input connections are made to terminal J1, polarity not important.


Connector Description
J1 Power 14-18V ac / 16-20V dc 50 VA
J2 Loco-I/O
J3 Loco-I/O
J4 RJ12 Loco-I/O
J5 RS232

DIP Switch settings

Dip switch # Function ON Function OFF
1 15mA current source to LocoNet signal line
N.B. this is default setting
No current source to LocoNet signal line
2 57600 Bd 19200 Bd
3 MS100 mode Loco-I/O mode

Current source, what is that?

Click here for a brief explanation about it.

Led functions

Led ON OFF Flashing
1 Power on Power off
2 LocoNet fault LocoNet OK LocoNet communicating

Connection cable for Loco-I/O*

The best suitable cable is Cat 5 Ethernet cable.
For all cables together a maximum length up to 200 mtrs is allowed.

GCA85 connections
Standard full wired male to female 'extension' Rs232 cables are allowed, but up to a certain limit.
It is never experienced how many can be used, but a few do not disturb the communication.
Please remind that this type of cable is not able to handle the full 3A of the power supply!

Connection cable for RS232 to PC.

Any full wired standard male/female 'extension' RS232 cable is suitable.
J3 (computer COM connector) could be replaced by direct USB connector.
Ask Peter for info.


Previous version MGV85

Schematic and partslist of previous version MGV85 V1.2:

The MGV85 schematic
The MGV85 partslist
N.B. ONly complete ordered kits will be supported!

Jumper settings MGV85

J1 Do not install this jumper.
J6 Set always for use with GCAxx or MGVxxx LocIo booards. Should be removed when Intellibox is connected to J4

gca85-en.txt · Last modified: 2024/06/14 00:03 by rainerk