Non-Sound Decoder MX600 - MX638 and Sound Decoder MX640 - MX659 Page 53
Explanation: Motors of model railroad locomotives are often equipped with choke coils and capaci-
tors, which are supposed to suppress or filter out electric noise caused by sparks arcing across the
motor’s brushes (causing poor TV reception etc.).
Such components impair the motor regulation. Compared to others, ZIMO decoders manage quite
well and there is hardly a difference in performance with or without those components in place. How-
ever, in recent years larger choke coils are being installed in many locomotives than was the case
earlier
– and these can noticeably compromise drivability.
The potentially “harmful” choke coils are often recognizable by their shape, as they look like a resistor
with color bands (in contrast to a wire wound ferrite bar). That doesn’t mean though that these choke
coils have a negative effect in all cases.
Lessons learned and accompanying measures…
ROCO, BRAWA, HORNBY
– so far present no problems, no action necessary.
FLEISCHMANN H0 with “Round motors” – choke coils are no problem; capacitors should be removed
if necessary, especially the ones between frame and motor (may destroy the decoder if left in place)!
Newer Bühler motors
– no problems so far.
TRIX H0
– choke coil between track and decoder plug should be removed!
MINITRIX, FLEISCHMANN PICCOLO
– very inconsistent; removing of capacitors is often advanta-
geous; choke coils on the other hand presented no problems so far.
Indications of a harmful effect of such components, besides a general unsatisfactory motor control
(jerking…), are:
- weak BEMF compensation: as confirmation, set the decoder for testing purposes to low frequency
–
CV #9 = 200
– and see whether the control compensation becomes stronger. If that’s the case, the
choke coils are most likely to blame.
- if a difference in compensation is noticeable between 20 kHz and 40 kHz (selectable in CV #112, Bit
5), it is very possible that the choke coils or capacitors are the cause.
Remedy
: Bypass choke coils
(or replace with wire strap)
!
Remove capacitors! Capacitors are less
likely to interfere with motor regulations.
Locomotives with 6 or 8 pin NMRA interface . . .
. . . are easy to retrofit with the MX...
R
, MX...
F
, MX...
N
(e.g. MX630R or MX620F) etc. They come
with the appropriate 8 (R) or 6 (F, N) pin connector. There is usually enough room provided in such
locos. Removing the dummy plug from the loco automatically interrupts all damaging connections and
the decoder can be plugged in instead.
In some cases it is necessary to hardwire some decoder leads besides just plugging in the plug. An
example of this is the MX630R that has more outputs available than the standard 8-pin plug has pins.
For hard-wiring of decoder leads use the explanations below.
Hard-wiring a loco
motive…
… with a DC motor and headlights:
This represents the
most common wiring diagram
for HO installations. All other diagrams that fol-
low are modified or extended versions of this one.
Red
Black
Orange
blue
Yellow
White
Gray
Right rail
Left rail
M
Headlights
Rear Front
DC Motor
Right
Left
Headlights connected as shown on this diagram are directional and switched on/off by the F0 key.
With the appropriate use of "function mapping" - CV's #33, 34, 35...
– it is also possible to control the
headlights independently with F0 and F1.
PLEASE NOTE: Body mounted light bulbs that are hard to isolate can be left as is. The body acts as
the power supply to the bulb. The blue lead from the decoder must not be connected to the bulbs in
such circumstances. The white and yellow leads are connected to the other side of the bulbs. The
brightness of the headlights will be reduced with such an application
. . . with an AC motor:
Two additional 1N4007 diodes (or equivalent
– min 1A) are required as shown in the diagram below
when installing a decoder in a loco equipped with an AC motor. They can be obtained at your local
electronic store or from ZIMO.
Red
Black
Orange
Blue
Yellow
White
Gray
Right rail
Left rail
M
Headlights
Rear Front
AC-m otor
Field coils
2 Diodes 1N4007
Rotor
Most locomotives with AC motors get the power supplied by a third rail, which is of no significance as
far as the motor hook-up is concerned. The above schematic is therefore valid for AC locomotives
running on two or three rail track (instead of “right rail” and “left rail” think “outside rails” and “center
rail”).
