I'm an electronic engineer asked to repair a number of these DCC control
that apparently plug into/under model train locos. I've found a few failings
testing cold but would like to apply some power to them.
Anyone know of "block diagram" pinning for such units or any technical info?
Boards are 32x30mm with surface mount components , 2x4 way connector, 21 way
conn, 5 x 2way and 1x 4w connector
Send them back to Zimo, I've had free repairs in the past. If you need
to replace the PIC, where are you going to get the firmware?
Marked 2395 X002 on the overlay
they are some sort of interface board, no PIC, only a 555 , one transistor
and a number of diodes and passives and all those connectors. So far 2 have
had duff lead-free soldering
cannot find reference to these boards on zimo.at
Has the same main connectors as this
Bachmann E-Z Command 8 Pin To 21 Pin Adaptor
bit bigger board plus outlet connectors, labelled on board, for LED1,
LED2, motor, R+ L- = rail pickups ?, Spk = speaker? and Aux1 which the
output of the 555 via the transitor goes to
21 pinning seems to agree this
I've read the thread, and my opinion is that it's hardly worth the
trouble, unless of course you want the "learning opportunity". Without a
model number, it's nearly impossible to say what the board is. A later
post by you suggests that it's a 21-to-8 pin adapter, not a DCC control
board (decoder) as such. If, as you say, some of the solder joints are
cold/defective, fixing them will likely fix the board. OTOH, if it
actually a decoder, then most likely the chip is defective.
The DCC decoders convert rail power (14-18V, 50/60HZ) to chopped DC
power (effective 0 to ca. 12V), and control other devices such as
locomotive lights, sound systems, etc. The decoders include EEPROM which
stores the control program, and "control variables", by means of which
the board's (ie, locomotive) address can be changed, and functions such
as speed control can be modified. The control is accomplished via data
packages transmitted from the control station via the rails to the
locomotive, at about 150KHz IIRC. Most of the control circuitry is
integrated into custom-made packages ("chips", in model railway parlance).
You can find more at nmra.org, search for DCC. NMRA has specified
recommended wiring harness colours, ie, pinouts for the board as a
whole. The internal pin assignments for any chips are the manufacturer's
responsibility/choice, of course.
You mention some on-board specs, I agree with your guess as to what they
mean. That is, if the board is an adapter, and not a decoder.
I'm not an electronics expert, the above comments are based on my
knowledge of DCC.
AIUI, DCC puts a digital signal on top of an AC propulsion current. The
latter is rectified to sine wave DC by the decoder, and is in turn
chopped to provide average voltages below the maximum, thus controlling
the speed of the locomotive. If this is incorrect, please elucidate.
The signal is delivered to the locomotive in the form of data packets,
whose format is specified in NMRA Standard S-9.1. This standard also
indicates that the propulsion current is AC, Vmax between 14 and 18V RMS.
My recollection of the propulsion current and the signal current
relationship is that the former is "ordinary" AC, ie, 50/60Hz, depending
on country, and the latter a high frequency, whose value I've probably
got wrong, because I wrote from memory. Kindly correct and elucidate my
No, the "propulsion current" and the digital signal are one and the
The DCC track voltage is a square wave digital signal and is rectified
to DC in the decoder.
That bit is correct.
S-9.1 is the electrical standard. The voltage limits depend on other
non-DCC scale specific standards.
Basic data packets are defined in S-9.2.
NO. "AC" does not mean 50 or 60Hz other than in the very limited
definition of household mains.
The country is irrelevant.
You've hinted at the NMRA specs, why not read them for yourself?
The system you are describing is more akin to Hornby's Zero One, long
Its not rectified at all its transformed into PWM feed to the motor the
frequency can be varied on some decoders so that they can be tuned to
particular motor types. Works the same way as DC PWM controllers.
The DCC signal is rectified to a DC supply in the decoder. Just look
at a decoder and you'll spot the 4 diodes that form the bridge
The DC supplies the microcontroller and the output H-bridge. The H-
bridge is driven by the uC to generate the PWM signal.