NMJ SKD224 User manual

SKD224 replacement board
Assembly Manual
- Document version 0.1.6 –
© Copyright NMJ 2016
All rights reserved

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 2 of 46
Please read this manual carefully before carrying out the
installation!!! Although our products are very robust, incorrect
wiring may destroy the module!
During the operation of the device the specified technical parameters
shall always be met. At the installation the environment shall be fully
taken into consideration. The device must not be exposed to moisture
and direct sunshine.
A soldering tool may be necessary for the installation and/or
mounting of the devices, which requires special care.
During the installation it shall be ensured that the bottom of the
device should not contact with a conductive (e.g. metal) surface!

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 3 of 46
Content
1. Important Information..............................................................4
2. Required tools..........................................................................4
3. Required materials ...................................................................4
4. Operation principle ..................................................................5
5. Board Connections...................................................................7
6. Disassembly of the SKD224....................................................9
7. Installing the replacement board............................................13
8. Replacement of the wheels ....................................................18
9. Decoder settings.....................................................................25
10. Programming tips...................................................................26
11. Analog operation ...................................................................28
12. Notes......................................................................................28
13. CV Table................................................................................29

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 4 of 46
1. Important Information
The manual is a guide to assemble the SKD224 replacement
board and gives some decoder setting recommendations and
programming tips. The replacement board is a drop in replacement
for the original board situated inside the SKD locomotives chassis.
The replacement board contains a DCC decoder and a Smart
Power Supply (SPP) and is suitable for DCC operation. The
decoders have installed a dedicated firmware with factory default
parameter values optimized for the SKD224 locomotives. After a
decoder reset, all the decoder parameters are reverted to the factory
default values.
Reference documents: NA
2. Required tools
- tweezer
- screwdriver
- right plier
- cutter
- cutting plier
- soldering station
3. Required materials
- SKD224 replacement board kit containing the replacement axles
- soldering wire
Estimated assembly time: 30-45 minutes

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 5 of 46
4. Operation principle
The SKD224 replacement board contains a smart power pack (SPP)
and is integrating a DCC decoder with BEMF PID motor control and
4 physical (function) outputs. The decoder controls the charging of
the on board 1 Farad capacitor, and ensures switching to the internal
power supply in case of track contact interruption. This guaranties a
trouble free running of the SKD224 even if the contact with the rails
is lost. The SPP is capable to power the locomotive up to 4 seconds
and can run it up to 30-50 centimeters without DCC power
(depending on the speed). This is especially useful for small 2 axle
locomotives like the SKD224, which has only a few current pickup
points, and suffer very often of DCC power interruption.
At start-up, the board will have a current consumption of 250-300
mA for up to 2 minutes, even if the locomotive is stationary. This is
normal, during this time the SPP is charging the internal capacitor.
In case of external power interruption, after the maximum allowed
timeout has been elapsed (this can be changed altering the specific
CV), the locomotive will stop. The operation can be resumed when
the locomotive is powered again over the rails.
Due to the operational principle, the SPP can be used only in DCC. If
the locomotive is used in DC, the SPP will be not activated.
The lights of the SKD224 are wired to the internal SPP circuit, so
even in the case of contact problems while running, during the
switching between external DCC power and internal SPP, the lights
are stable, and no annoying dimming is visible.
Connections for optional front/rear lights and electrical couplers are
available at both ends of the boards.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 6 of 46
The on board decoder is full of options: is featuring a SUSI
connector for optional sound module connection, contains Zero
Speed and ABC Braking, with penduling (push-pull operation), has
a RailCom transmitter, and is capable of driving different electrical
couplers. Future options can be also integrated with a firmware
upgrade.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 7 of 46
5. Board Connections
(the color coding is made according to NMRA standards, otherwise noted)
Motor Negative Terminal
Motor Positive Terminal
Coupler
Common
Coupler Output
Coupler Output
Coupler
Common
Right Track Connection
Left Track Connection
Lights
Common
(See note 1)
Lights
Common
(See note 1)
Front
White
(See note 2)
Rear
White
(See note 2)
Front
Red
(See note 2)
Rear
Red
(See note 2)

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 8 of 46
Note 1: The positive common terminal for the optional lights
(brown color in the illustration) is not the same as the coupler
positive common (blue in the illustration). It is forbidden to
connect them together.
The front/rear light outputs (white and yellow color) allows
direct connection of LEDs, so no current limiting resistors are
needed. The resistors are integrated to the boards. The Anode
of the LEDs must be connected to the Lights Common, while
the cathode to the front/rear outputs.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 9 of 46
6. Disassembly of the SKD224
Remove the housing from the chassis. Press in the same time on both
ends of the housing (1), and lift (pull) the housing in the upper
direction (2).
The housing has 4 plastic ears (3), which enters in the 4 recess of the
chassis (4). Using a sharp blade (cutter) can help in the extraction.
1
1
2
3
3
4
4

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 10 of 46
Gently remove the housing, and place it on its side near the chassis.
Do not pull it too far, since the cabin lighting has a cable connection
to the chassis (2). The cabin itself also has 2 plastic pins (1), which
fits in the corresponding openings in the base plate located above the
chassis.
2
1

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 11 of 46
Disconnect the cabin lighting by removing the connector from the
chassis printed circuit board.
Localize the track connections (1), motor connections under the
black adhesive tape (2) and the mounting screws (3) on the chassis of
the locomotive.
1
1
2
3
3

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 12 of 46
First, unsolder the connection wires (4 in total).
Remove the 2 screws (1), and lift the printed circuit board. Please
note, that there are 2 mechanical centering pins (2) in the chassis,
which will guide the fit of the replacement board.
2
2
1
1

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 13 of 46
7. Installing the replacement board
Lead the 4 connection wires thru the corresponding holes in the
replacement board, and fit the board to the chassis using the
mechanical centering pins. Screw the board to the chassis.
Solder the wires to the replacement board.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 14 of 46
All the wires must be pulled back, and arranged under the printed
circuit board. The motor connection wires must be arranged in such a
way to not touch the flywheel.
The track connection can be arranged on both sides of the chassis in
the available cutouts. If needed, a small drop of cyanoacrylate can be
used to fix the wires to the chassis.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 15 of 46
Half of the small adhesive tape from the original board can be used
to mask the side lighting of the LEDs of the central head lights.
Before reassembling the housing, removal of 2 small inside walls (1)
is necessary to assure the required space for the replacement board.
1

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 16 of 46
This operation has to be performed using a cutter and a small plier.
The 2 interior walls must be cut with extreme care as close as
possible to the housing external wall without damaging it. After the
operation, clear the debris.
Insert the cabin light connector to the counterpart in the replacement
board.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 17 of 46
Insert the housing over the chassis, and press down until the plastic
ears fit the recesses of the chassis. The plastic ears of the cabin also
have to be fitted to the base plate.
After the housing is in its place, press the base plate in upper
direction while fitting the cabin plastic ears, till there is no distance
between the base plate and the housing.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 18 of 46
8. Replacement of the wheels
For the wheels/axles replacement, turn the locomotive upside down,
and place it on a stable surface to avoid falling on its side.
Pull the plastic ears on both sides of the base plate with a small
screwdriver to release it from the chassis (1). Lift the base plate in
upper direction (2).
1
1
2

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 19 of 46
Remove the 2 original axles with the plastic toothed wheels from the
chassis. The axle’s assembly keeps the current pickups pressed to the
wheels, while removing them the current pickups will depart from
the chassis.
At this point since there is access to the gearbox, it could be a good
idea to apply some grease over the wheels if needed. However, this
can be done at a later time too. You can use Roco type grease part
number 10905.

SKD224 replacement board
Assembly Manual
Document
Version
0.1.6
Page 20 of 46
In the illustration an exaggerated quantity of grease is applied for
exemplification. Use the grease in a moderate quantity.
Apply it also on the intermediary toothed wheels too.
Insert the replacement axles with the brass toothed wheels. They
must be inserted starting from the inner side of the chassis (1),
moved to the correct position (2) while pressing the elastic current
pickups to touch the wheels from their inner side (3).
2
1
3