On 13/05/2011 9:12 AM, N_Cook wrote:
I'm an electronic engineer asked to repair a number of these DCC control
boards
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

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.

HTH
Wolf K.