N Gauge Thomas DCC Conversion

[Ch4lkst3r]

Hi,

 

I've acquired a Bachmann N Gauge Thomas (from America) which isn't DCC ready and is very small but my layout is DCC.  I've taken him apart (somehow feels slightly wrong) and it has this little PCB inside with two things labelled 6R8 on the PCB (see picture) along with 4 wires helpfully labelled R, L, M+ and M-.  Now I know the meaning of the wires (R = right hand wheel pickup, L = left hand wheel pickup, M+/M- = motor + and - connections) but as I'm adding a DCC chip can I just remove the existing PCB and replace it with the decoder connecting the wires accordingly?  I don't know what the two 6R8's are or do so I've come to you helpful people.

 

Thanks,

 

Iain

 

[Ch4lkst3r]

Doing some more research I think the 6R8's are inductors/chokes.  There's nothing else on the board and the decoder I believe will do the job of those so I can just remove the PCB and connect the decoder to the wires accordingly.  At least I think that's right?

[Jim Easterbrook]

I think the 6R8 components are 6.8 ohm resistors. http://www.marsport.org.uk/smd/res.htm

I don't know enough to suggest why they're there.

[Ch4lkst3r]

3 hours ago, Jim Easterbrook said:

I think the 6R8 components are 6.8 ohm resistors. http://www.marsport.org.uk/smd/res.htm

I don't know enough to suggest why they're there.

 

Following further research and a little test with a multimeter if my basic knowledge of electronics I think they're inductors still.  I've tested the resistance using the ohm setting and it shows zero across the 6R8 thing (the same as if I connect the two probes together).  Google searches seem to imply that this means they're inductors otherwise I'd get a figure for the resistance.

[jpendle]

It's probably a 6.8uH inductor. The R is used where the decimal point should be.

 

Regards,

 

John P

[Ch4lkst3r]

2 minutes ago, jpendle said:

It's probably a 6.8uH inductor. The R is used where the decimal point should be.

 

Regards,

 

John P

 

That's my thinking too John.  If that's the case can I just remove the board and attach the decoder to the relevant wires?

[Jim Easterbrook]

13 hours ago, jpendle said:

It's probably a 6.8uH inductor. The R is used where the decimal point should be.

 

How confusing. 25 other letters to choose from...

[Hamburger]

• Type in '6R8' on Google and you'll find many similar components.
• 6R8 means 6.8µH which makes sense at this position on an analogue circuit board.
• You have measured a resistance of nearly 0 ohms

For me it is 99% clear that you have to remove the PCB.

[melmerby]

They are inductors to form part of the electrical noise suppression circuit.

They can be left in circuit but are unnecessary when using a DCC decoder, so can be safely removed (i.e. the complete board)

The four wires would then connect to the appropriate wires on the decoder.

 

Edit

There may well be a capacitor across the motor terminals as well, that can also be removed.

 

Edited February 28, 2021 by melmerby

[Steven B]

One of them looks to be marked "L2" on the PCB which makes them inductors. The other should have a "L1" marking somewhere nearby.

 

I'd be tempted to remove the inductors and solder the decoder wires to the pad that are left behind.

 

Steven B.

[Ch4lkst3r]

1 hour ago, Steven B said:

One of them looks to be marked "L2" on the PCB which makes them inductors. The other should have a "L1" marking somewhere nearby.

 

I'd be tempted to remove the inductors and solder the decoder wires to the pad that are left behind.

 

Steven B.

 

The other does indeed have L1 next to it.  There's nothing else on the board so I'm going to remove it and then connect the wires accordingly once Pat has delivered the decoder.

 

Thanks for the help everyone