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
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
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 errors.
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.