Quick little picture puzzle for you decoder experts

[OldEastRR]

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On this cut-down decoder from a Bachmann DCC tender, where would I attach the wires to light the front headlight?
There is markings on the board -- next to the RH screw is "L+" and "L-" holes for wires to be soldered. Is that where they go? The RH list of markings and holes are for I think hardwiring a new decoder; I seem to have run all the other wires from the LH list.
So what's the verdict?

[peteski]

Long time ago I decoded a Bachmann tender's circuit board (the one without a decoder) in this thread and the A-board.  Unfortunately the photos are gone.  Not exactly like your board but Bachmann seems to have used the same nomenclature for marking connections.

Here is an excerpt from that thread:
That cable carries the positive (M+) and negative (M-) motor connections, positive (L+) and negative (L-) headlight connections and redundant positive (R) and negative (L) track connections. I say that those are redundant because those connections are already made through the tender's draw bar. ... They also connect (through 2 diodes and a resistor in series) the headlight pins (L+, L-) to the rail pickups.

The black wires (the umbilical cord) going to the loco hast the front headlight connections (L+ and L-).  If you are replacing this decoder, wire the L+ to the new decoder's blue wire and L- to the white wire. Don't forger to add a series-resistor into the circuit (as the Bachmann decoder most likely had that resistor on-board).

Having said all that, I am not familiar with that specific decoder - just offering an educated guess.

[OldEastRR]

The lettering next to the terminals that have wires to them go down in this order
R
M+
not sure
not sure (poss M-)
not sure
L
There are six wires to the loco, all black
Just to it's left are two open terminals marked
L+
L-

[peteski]

That photo is not very clear but I could swear that I see 2 black wires soldered to the terminals marked L+ and L- .

The 6 wires to the loco are most likely R and L (right and left track pickups or red and black on the new decoder), M+ and M-  (motor leads - orange and gray on new decoder), and L+ and L- (headlight blue and white wires on the new decoder).

[jdcolombo]

I think the terminals  you want are the LF- and L+ terminals on the shorter board, NOT the L+ and L- terminals on the longer board.

There's an easy way to check this.  If you have a multimeter (and if you don't, spend $30 on a low-end digital multimeter from Radio Shack; you're going to need it if you are going to do any sort of electronic tinkering with engines and particularly with DCC), solder wires to the L+ and LF- terminals.  Clip the positive (Red) wire from the multimeter to the L+ and the negative (Black) to the LF- wires.  Set your multimeter to read DC volts; if it has different ranges (most do; marked next to the large knob that selects them), us a range that is zero to 100.

Now put the engine on the track, select it on your DCC system, and crack the throttle just to make sure you actually have control of it and if you do, set the throttle back to zero.  Now look at the multimeter.  If the wires are connected to the front headlight, the meter should read zero.  Now press F0 (e.g., turn the headlight on using the DCC system) with the engine set to run in the forward direction.  The meter should read something around 10v (it might be 9 or 11 or 12, depending on your track voltage).  If it does, you have the headlight connections.  Wire your headlight up, and if using an LED, use a 1K dropping resistor unless you are sure that the headlight already has one attached in the boiler.  If you are not sure, use one.

If you don't get any voltage from L+ and LF-, then try LR-.  That should be the rear headlight connection, but . . .

I would NOT use the L+ and L- connections on the large board.  If this setup uses a base circuit board with a "plug in" decoder on top, then the lower board connections are probably for DC operation, not DCC operation.  Again, you can check this with your multimeter by soldering two wires to these terminals, putting the engine on the track and checking what the meter says.  If you get voltage from those terminals with the engine just sitting on the track and not selected on the DCC system (and F0 off), then that is a DC operation connection, not a DCC connection.  You probably don't want to try powering a headlight from this with an engine set up for DCC.

John C.

[Greg Elmassian]

Guys, check out this PDF:  http://www.bachmanntrains.com/home-usa/dwg/dwgs/N_BALDWIN_4-6-0_EXPLODE_DRAWING_N514X_(1).pdf

Certainly appears to be the same decoder...  has all the information

Greg

[peteski]

That sure explains it all.  I was thinking that Al was planning on totally removing the circuit board and was trying to decipher the legends on the terminals with the black wires (closer to the screw), not the still-unused terminals at the breakaway point.

[OldEastRR]

I think the terminals  you want are the LF- and L+ terminals on the shorter board, NOT the L+ and L- terminals on the longer board.
John C.

When you say "long board", do you mean the RH row of holes? The instructions say that's where you wire in a new decoder if you want to replace the Bachmann one.

[OldEastRR]

So far this hasn't been a DCC disaster like my others, the loco always ran fine on DCC. In my quest to get the light working I discovered (after tracing the wires) that I had hooked them to the two middle holes on the LH side. So I expected the light to be burned out, but it still works! I hooked it up to 5v battery stack and it's fine. Happy! Happy! So I need to get the voltage from the L+ and L- holes to be only 5 volts. Apparently those two middle holes aren't connected to anything.
Tho this 10 wheeler has absolutely no place on a 1955 NH scene, it's cute. Besides I got it free. And it runs on DCC and the light lights! WOW!

[jdcolombo]

When you say "long board", do you mean the RH row of holes? The instructions say that's where you wire in a new decoder if you want to replace the Bachmann one.

Yes, the RH row of holes in your photo.

Are you wiring up an LED?  If so, don't worry about the voltage; just use a 1K dropping resistor on the LF- wire and you'll be fine.  If you're using a bulb, then you are on your own.

John C.

[OldEastRR]

This wasn't a problem thread, just an inquiring one, and I'm happy to say the right wires got attached to the right holes on the board and the 4-6-0 now runs with a working headlight. So I'm closing this thread.