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GCA108 LocoNet booster


By Peter Giling

Power Unlimited

Rocrail features a Power Manager supporting this booster.

The standard available booster bus topologies in the market have the undesired behavior of shutting of all, if one booster experiences a short circuit.

The idea was to make individual inputs on each connected booster to be able to switch them on / off separately.

This could only be achieved with additional in and output to the booster and a program to make it possible.

Rocrail is the program which supports all these features, and since all MGV/GCA units are more or less based on LocoNet, this LocoNet should be part of the booster.

The next problem with boosters connected to Loconet thus RailSync, is that they are getting a DC output over the RailSync lines when a General Power Off is given.

This causes problems with some decoders, which are switching back to analog control and thus running away in high speed.

This booster is also taking care for that. Within the 30 mSecs spec, after the Railsync pulse has become DC output, the booster shuts off output.

An internal short circuit detection is provided for maximum security, which switches off the booster and signals the problem via LocoNet to Rocrail.

There decision is made if all other boosters should be switched off.

LocoNet is a trademark of Digitrax, Inc.


  • Powerful 3A output with standard single 16V transformer.(O/G scale output needs 18Vac)
  • Selectable output for N, HO or O/G.
  • Internal short circuit detection shuts off output.
  • Power output selectable between 1 OR 3 Amp max.
  • Opto-coupler isolated connection between rails and LocoNet.
  • Opto-coupler isolated connection between rails and Railsync.
  • Quick flashing LED when short circuit occurs.
  • Slow flashing LED when no pulse is detected.
  • Digital signal detection; power off within 30ms to prevent mobile decoders to go into analog mode
  • Sensor report for short circuit events
  • Sensor report for track power state
  • Input for controlling track power
  • 13 extra programmable I/O's in LocoNet.


First prototype:

The complexity made it necessary to design in double sided. However, only a few -easy to reach- points have to be soldered at the top layer.

In this latest test version V2.1, a solid cooling devide is used.


Jumper Open Closed
JP 1 report loconet input states at startup No report at startup
JP 2 Power output 3Amp maximum Power output 1 Amp maximum

Switch SW1 1 2 Scale Output

LocoIO port Function Setup Connector
1 user defined - J7(3)
2 user defined - J7(4)
3 user defined - J7(5)
4 user defined - J7(6)
5 user defined - J7(7)
6 user defined - J7(8)
7 user defined - J7(9)
8 user defined - J7(10)
9 user defined - J8(1)
10 user defined - J8(2)
11 user defined - J8(3)
12 user defined - J8(4)
13 user defined - J8(5)
14 short circuit / no pulse indication to loconet block
15 Booster indication OFF(= high) / ON(=low) input
16 Booster start command(Low = on) switch + C2

Short circuit indication (p14) needs to be set to block, since output is flashing.

Use the Programming Dialog to setup the I/O.

Led functions

Leds indicated from left to right from version 1.5
Led # function action LocoNet I/O
LE6 Loconet On = LocoNet OK
Off = LocoNet not connected
flashing = LocoNet activity
LE1 GCA108 supply On = Power OK
Off = No Power
LE5 Booster On/Off On = Booster OFF I/O 15 high
On = Booster ON I/O 15 low
LE4 Railsync/short circuit Off = Normal I/O 14 high
quick flash = Short circuit detected I/O 14 + 15 low
slow flash = No Railsync I/O 14 + 15 low
LE2 Railsync indication On = Railsync OK
Off = No Railsync
LE3 Railpower indication On = Railpower OK
Off = No Railpower


Connector J3
Pin function
1 Rail power +(-)
2 Rail power -(+)
Connector J4 ( for connection cooling fan )
Pin function
1 0V
2 +5V
3 0V
Connector J6 Supply power 18VAC 54VA
Pin function
1 Supply Power
2 Supply Power
Connector J7 Loconet I / O connection header
Pin LocoIO port
1 + 5V
3 1
4 2
5 3
6 4
7 5
8 6
9 7
10 8
Connector J8 Loconet I / O connection terminals
Pin LocoIO port
1 9
2 10
3 11
4 12
5 13
8 +5V
Connector J9 Loconet DB9 male
Pin LocoIO port
2 Railsync -
3 Loconet signal
4 Railsync +
5 +V supply
7 n.c.
8 n.c.
9 +V supply
Connector J10 Loconet DB9 female
Pin LocoIO port
2 Railsync -
3 Loconet signal
4 Railsync +
5 +V supply
7 n.c.
8 n.c.
9 +V supply

Connection cable

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

DB9 female wire colour DB9 male function
1 blue + blue/white 1 GND
2 orange/white 2 Railsync -
3 green 3 Loconet signal
4 orange 4 Railsync +
5 brown 5 +V
6 green/white 6 GND
7 not connected 7
8 not connected 8
9 brown/white 9 +V

Standard full wired male to female 'extension' Rs232 cables are allowed, but will cause problems when many of them are used.

However, a few do not disturb the communication.


The parts positions are visible at page four of pcb files.

mgv108-en.txt · Last modified: 2018/11/12 08:56 (external edit)