Which way round for Bachmann 6 pin n gauge decoder

[TomJ]

Yet more questions from this clueless newby! I have just brought a few Bachmann 6 pin 36-558 decoders. There seems to be no indication at all as to which is pin 1 or 6, and most of the unit is covered in a head sink

The instructions say that the plug is arranged to there will be no damage which ever way it's inserted. So I put it in to my Farish 108 turned it on and there was a spark, a puff of smoke and a nasty smell! Turned it round and it runs fine in one direction but not at all the other way. Lights work in both directions. Clearly I have ruined the decoder (and lost £15) but is there a way to tell which pin is which before I fry any more?

 

Thanks

[Nigelcliffe]

1 -  ask your retailer, or Bachmann.

 

2 - clearly you have a sale of goods claim on the decoder.  Its a Bachmann Decoder, installed in a Bachmann Product, following Bachmann's instructions.   If it goes "puff", then "sale of goods" applies, and ask for refund/replacement.   The claim is against the retailer (that's UK/EU law, the retailer then takes it up with the manufacturer). 

 

However, on (2),  I would be suspicious of a short circuit inside the loco, possibly the pins from the PCB to the motor brushes.   I've seen shorts in this area in 108's before. 

[Adrian Wintle]

I never understood why the 6-pin spec wasn't fail-safe like the 8-pin spec.

 

The spec is:

Motor Right

Motor Left

Rail Right

Rail Left

Headlight Front

Headlight Rear

 

I would have thought a better spec would have been:

Motor Right

Headlight Front

Rail Right

Rail Left

Headlight Rear

Motor Left

 

The first is dependent on the decoder design to prevent damage if inserted the wrong way around, while the second should prevent any damage whichever way arount the decoder was inserted.

 

Typically, pin one should be indicated by a mark or dot on the board or cover.

 

Adrian

[Izzy]

I would endorse all that has been said. For a product that should be just a simple push fit into a socket, the general and normal lack of easy identification and verification of the correct orientation is quite common with all makes of 6-pin chip.

 

To answer your specific query here are a couple of shots of the Bachmann 6-pin with the no.1 pin having a white dot. They should all have this as identification, but usually don't. You will see that the 'top' of the socket is higher up this way around.  

 

Hope this helps.

 

Izzy

 

 

 

[Crosland]

Unles the loco wiring is faulty (which could cause damage either way) It is fail safe the way it is.

 

Normally you would have:

 

Decoder -> Socket

Motor Right -> motor A
Motor Left -> motor B
Rail Right -> rail A
Rail Left -> rail B
Headlight Front -> front lights
Headlight Rear -> rear lights

 

With the decoder reversed:

 

Decoder -> Socket

Motor Right -> rear lights
Motor Left -> front lights
Rail Right -> rail B
Rail Left -> rail A
Headlight Front -> motor B
Headlight Rear -> motor A

 

The DCC reversal from the rails is immaterial unless you are using Asymmetric DCC.

 

If a motor output switches low it will pull current through the lights from the blue wire. The resistance of the bulb, or LED ballast resistor, will limit the current to a safe level.

 

The function outputs are open collector (designed to be connected to the +ve blue wire through a load) so there is no current path through the motor whatever they do.

 

Andrew

Edited January 24, 2014 by Crosland

[Adrian Wintle]

Unles the loco wiring is faulty (which could cause damage either way) It is fail safe the way it is.

 

Normally you would have:

 

Decoder -> Socket

Motor Right -> motor A

Motor Left -> motor B

Rail Right -> rail A

Rail Left -> rail B

Headlight Front -> front lights

Headlight Rear -> rear lights

 

With the decoder reversed:

 

Decoder -> Socket

Motor Right -> rear lights

Motor Left -> front lights

Rail Right -> rail B

Rail Left -> rail A

Headlight Front -> motor B

Headlight Rear -> motor A

 

The DCC reversal from the rails is immaterial unless you are using Asymmetric DCC.

 

If a motor output switches low it will pull current through the lights from the blue wire. The resistance of the bulb, or LED ballast resistor, will limit the current to a safe level.

 

The function outputs are open collector (designed to be connected to the +ve blue wire through a load) so there is no current path through the motor whatever they do.

 

Andrew

 

But the Motor Right and Motor Left are intended to be connected to each other via a load (the motor), not intended to be connected (shorted) to track power ('blue wire') through a small load that may or may not have diode protection (and then likely only in one direction). Similarly, the Headlight Front and Headlight Rear are not intended to be connected together through a load, but are intended to connect through to track power ('blue wire') . If the decoder has been designed without allowing for protection to handle these cases (i.e. cheaply), you could potentially cause damage to the decoder by plugging it in backwards, in the same way that you can by having a short in your wired installation. By having the pinouts symmetrical you wouldn't have to worry about it.

 

Adrian

Edited January 24, 2014 by Adrian Wintle

[Crosland]

But the Motor Right and Motor Left are intended to be connected to each other via a load (the motor), not intended to be connected (shorted) to track power ('blue wire') through a small load that may or may not have diode protection (and then likely only in one direction).

Having designed decoders and looked at other designs I can assure you that either motor output can safely be connected to the blue wire through a bulb or LED with ballast resistor. The current will be well withinn the capability of the motor output.

 

Similarly, the Headlight Front and Headlight Rear are not intended to be connected together through a load, but are intended to connect through to track power ('blue wire') . If the decoder has been designed without allowing for protection to handle these cases (i.e. cheaply), you could potentially cause damage to the decoder by plugging it in backwards, in the same way that you can by having a short in your wired installation. By having the pinouts symmetrical you wouldn't have to worry about it

If you are so sure, please explain how the damage occurs.

 

When both functions outputs are off, both sides of the motor are floating and no current flows. If either is on, the other is still floating and no current flows. If both are on then both sides of the motor are at the same potential and no current flows.

 

Andrew

[TomJ]

Thanks for all the help - especially the pictures. Much appreciated.

 

I still believe this is a poor design by the manufactors. Something sold as plug and play should be exactly that and I shouldn't have to have any knowledge of how it works or what connector goes where. It would be so simply to put a clear mark or number on it, or the cover, but the instructions don't even mention this

[Brian-1c]

I have an issue with my GF Class 24 and a Bachmann 36-568A. The loco diagram seems to show where pin 1 is, but the decoder does not. The decoder does, however, show which pin is motor right.

 

The loco runs fine with the blanking plug as an analogue loco.

 

It does not run with the decoder plugged in and address 3 selected. However, if I change direction, the lights front and rear change. 

 

Do I have the decoder in the wrong way ?

[Butler Henderson]

Sounds like it, if you have it the wrong way the function outputs are is connected to the motor and the lights to the motor outputs. The pick ups will be reversed in their connectivity. Just turn it round.

Edited April 3, 2021 by Butler Henderson

[Brian-1c]

I turned the decoder over to reverse the pins and it is much worse that way. Totally dead, no reaction, no lights, F0 does not respond, no movement on address 3.

 

The loco shows which pin is which on the dummy plug and the loco board, as shown here, top picture.

 

The decoder does not, as previously seen. But there is a nice picture. Now that shows the chip in the same orientation as the dummy plug, pin side down.

 

However, it would be really helpful if, for example, "motor right" said Pin 1 also. Unless that is wrong.

 

Please tell me if Motor Right is Pin 1, or Pin 6.

 

 

 

 

 

 

[Butler Henderson]

1 Motor right 

2 Motor left 

3 Right rail pick ups 

4 Left rail pick ups 

5 white function

6 yellow function

 

 

 

 

 

 

 

 

 

 

 

 

 

[Brian-1c]

Thank you Butler, much appreciated. Now, of course, I have also found the dccwiki page for NEM651. But I'll keep that for reference, as this is my first ever DCC ready loco with a socket - and I thought that would be lots easier.

 

Anyway, took the blanking plug off again and re-fitted the decoder as before, upside down with reference to the blanking plug, now that I know that pin 1 is indeed motor right.

 

Talked to it sternly and, it all works as advertised !

 

Lights work, on/off and directional. Loco moves, in either direction and is performing well.

 

Thank you for all the help, it is appreciated.