Bachman 2-8-0 Install Problem

Bachmann Spectrum 2-8-0 Consolidation
Decoder Installation [Problem] as of 5-98
2001
by Don Crano

Note: This problem has been corrected with Bachmann's second release of this locomotive. Unless you have a first release edition, or are not sure, this page will not mean anything to you. But based on the reports of others, and their findings, there is a problem with the NMRA socket in the tender of this loco.

This is a fine Loco, looks great, runs good and has some nice new features. Bachmann has done a great job on this loco.
This is the first DCC ready Steam engine to hit the market. The PCB and NMRA socket are in the tender as well as two plug and sockets to connect the loco to the tender. The loco is all wheel pickup, yep 10 wheels to pick up power. The drive is a toothed belt, that keeps the gearing out of sight and allows for a quite drive system. And comes complete with E-Z mate couplers. There is plenty of room in the tender for a decoder, and there should be no problem putting a sound system/decoder in there. The coal load is easy to remove, and can be drilled to act as a speaker grill. The full stall current of the motor is 1.10 amps.

When you install a DCC decoder with plug in this locomotive and tell the locomotive to go forwards, the locomotive will instead run backwards. Hopefully this mistake will be corrected and Bachmann as a responsible manufacturer will alert its users of the problem.

Using the pin numbers that are clearly numbered on the underside of the board (it would sure have been easier if pin 1 was identified on the top of the board). Pin 1 on the Bachmann 2-8-0 is the front fireman's side of the socket

Pin #

1
2
3
4
5
6
7
8

NMRA RP-9.1.1

Motor Brush[+] -> from right rail.
Rear Headlight.
Blank or F1.
Left Rail Pickup.
Motor Brush[-] -> from left rail.
Front Headlight.
Common Function +
Right Rail Pickup.

Bachmann 2-8-0

Motor Brush[-] -> from left rail.
Front Headlight.
Blank.
Right Rail Pickup.
Motor Brush[+] -> from right rail.
Rear Headlight.
Common Function +
Left Rail Pickup.

1)	And the easiest to do. Use a decoder that supports the setting of reverse direction (CV-29 bit 0) and ensure that CV29 always had an odd value (bit 0 is set)

2)	This is the decoder PLUG not the loco socket. Remove the green wire from the plug (if present) on pin 3, solder a jumper between pin 3 and 7 and insert the plug so that pin 1 is at the rear of the tender.

3)	This is the loco SOCKET not the decoder plug. Remove the circuit board from the locomotive and move the trace from pin 3 to pin 7, disconnect the connection to pin 3 and insert the decoder so that pin 1 is at the rear of the tender.

4)	The true fix, and hopefully what Bachmann will do in time. Rewire the circuit board correcting the 6 incorrectly wired pins.

NOTE: There is one other problem with this loco. There is a capacitor and 2 coils on the PCB, that form a filter that act to cut down interference from the motor brushes. If this loco is used in Analog mode, that is with out a decoder. The capacitor will act as a heavy load or short circuit. It will cause wheel tender wheels to pit, and has actually tripped the shut down of some boosters. Once a decoder is installed, this is no longer a problem. But if you plan to use this loco in Analog mode on a DCC system very much, I would suggest you cut one of the leads on the capacitor till you get a decoder installed.

Thanks to Larry Puckett for the discovery and to Stan Ames for the reasons and fixes.

The above picture is of the newer corrected PCB for the Bachmann Spectrum Series. The original PCB did not have R the resistor that is connected above the PCB to the junction of D the diode and C the choke. This does correct the problem with lights and un-like the first release above does not require CV29 bit 0 have an odd value.

Also note: That with the release of newer high speed decoders, those that are called silent, high frequency, super sonic, etc, the little yellow capacitor at the top right of the PCB becomes more import then just with analog, '0 pulse stretching on DCC' then it was. With these new decoders it must be cut, one leg will do as shown above. Also there is still no reason to cut out the chokes 'C' in the picture, they do not cause any problems, and if they are removed a jumper wire would have to be installed in their place.

What we have is a noise filter consisting of two chokes [coils] and a capacitor. The two chokes are in series with the two motor leads and capacitor is in parallel with the motor. This results in power reactive circuit, or a noise suppression circuit. The idea is to reduce possible noise generated from arcing at motor brushes, wheel rail contact points and so on. The problem is with the higher speed decoders, the high transition speeds of the decoders PWM outputs to the motor, the capacitor wants to short them out, just like it was noise. The result is Poor, erratic DCC speed control. Simply cutting one leg of the capacitor as shown in the picture solves the problem by disabling the noise suppression circuit, and besides the decoders onboard electronics already have any required circutry.

Bachmann has started to release their locos with decoders already installed. This has resulted in even another or 3rd release of the PCB. This one does not have the resistor and diode as above, the chokes are still there though. With this newer release there is no problems at all should you want to change decoders. Also the The Soundtraxx LC280 is unsuitable for this tender configuration.

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