# Looking for information about old Sierra Soundtraxx board



## rogern (Sep 5, 2016)

Hi, this is my first time posting in this forum.

At a garage sale yesterday I acquired a dusty LGB 2119D (Lake George and Boulder) as part of a small collection of G scale stuff that I bought. I wasn't sure if it would even run, but it was LGB so I figured that there was a chance. When I got home, I was happy to see that it did run, but I was also surprised when an aftermarket sound system fired up in the tender as well. The sound worked very intermittently and only a few times when I applied a higher voltage. 

I disassembled the tender and believe that what I have in there is an old Sierra Sountraxx board. After doing a bit of research (including on this forum), I believe that that problem is that the old rechargable battery 6V brick is permanently dead. I know that the sound won't work until I replace the battery. However, I've also noticed a broken wire connected to the Sierra card terminal #16 and I'm not sure where it goes. I was wondering if anyone could point me to a manual or schematic that might show me how the Sierra card is connected for standard track power (not DCC). Any help would be appreciated.

Roger


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## Stan Cedarleaf (Jan 2, 2008)

Hi Roger... I have the manuals in digital form... Email me and I'll get one to you right away..

[email protected] Put Sierra Manual in the subject line..

PS... Don't apply more than */-14 volts to the track. The Sierra board is limited to the lower voltage. They're not "fixable" any more. 

Here's an image of the wiring diagram for the Steam module.. 










And an image of the wiring for a voltage regulating circuit shown with a Diesel module but would be the same for a Steam Module. This circuit is not essential if you limit the voltage to 12-14 volts.


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## Greg Elmassian (Jan 3, 2008)

wow, not a voltage regulator at all, but just a resistor to drop a certain amount of voltage. The voltage "reduction" varies directly with the current drawn, so that's a scary circuit to an electrical engineer.

Greg


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## rogern (Sep 5, 2016)

Stan,

Thank you for this. It looks like my mystery wire connected to Sierra board #16 isn't really vital for anything. (I don't even know what a coupler/trigger switch is, but I'm pretty sure I don't have one).

Roger


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## Greg Elmassian (Jan 3, 2008)

grounding that wire causes a "coupler crash" sound, 2 couplers mating.

Greg


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## Dan Pierce (Jan 2, 2008)

I have 2 sierra sound units in my 2 SD45 and always run with up to 20 volts. I did replace the batteries in both and never installed the resistor. I guess I was lucky that they still work!!.


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## Dan Pierce (Jan 2, 2008)

Also, the manuals I have show the Sierra tied to the Zimo MX66 decoder which operates up to 24 volts, so I wonder if the 14 volts stated above is for HO sound units, not the older large scale sound units I have in my engines.


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## rogern (Sep 5, 2016)

Well, I appreciate all the advice. I was able to get the sound card working after replacing the old gel cel battery with a NiMh battery pack. I just left the coupler wire unconnected.

Speaking of power, I did notice something odd. Everything (loco and sound) works great forward and backward when I use a TrainPower controller (straight DC?). 

When I use my Aristocraft controller, everything works when moving forward. When I try to move backward, the controller shows an overload...until I turn off the sound card. Then the loco moves backward. All I can figure is that the Sierra card has an issue with pulse power when I try to go in reverse. Not a big problem, but unexpected.


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## Greg Elmassian (Jan 3, 2008)

Sounds like a direct short... 

The soundtraxx sierra was designed for battery... if you run it from track you need to put a full wave bridge between it and the track, it will not work with reverse polarity.

The board is marked and the polarity of power CANNOT be reversed.

If you need a circuit diagram to show the full wave bridge, email me. (real email, not pm)

For now stop running it backwards, you might damage the board.

Greg


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## Dan Pierce (Jan 2, 2008)

The manuals I have include the tech manual/diagrams which show power connections for various configurations of track and battery.


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## Stan Cedarleaf (Jan 2, 2008)

Hi Dan...... I have the older Tech Notes 6 and 7 in pdf form as well... 

If anyone would want them, just email me or use the links below.. 

Tech Note #6 for older RCS, Loco Link, Etc. http://1stclass.mylargescale.com/stancedarleaf/Sierra_Manuals/Tech6.pdf

Tech Note #7 for DCC decoders http://1stclass.mylargescale.com/stancedarleaf/Sierra_Manuals/Tech7.pdf

REVOLUTION diagram http://1stclass.mylargescale.com/stancedarleaf/Sierra_Manuals/Sierra%20Steam%20REVOLUTION%20Diagram_1.pdf


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## Greg Elmassian (Jan 3, 2008)

Yes, unfortunately, the pictures already posted, while they are "official" are MISLEADING, you cannot hook the Soundtraxx directly to the powered track and change polarity.

If you read the manual, they say "cut the pickup wire to the track and use that wire"... but the picture shows the wire still connected to the wheels and rails.

Later pictures in the manual show for track power you need a full wave bridge to GUARANTEE positive and negative to the CORRECT places on the board.










Greg


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## mendoFrank (May 2, 2015)

I should have known to come here first. My loose Sierra K37 card may now come to life. Stan, thank-you!


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## Dan Pierce (Jan 2, 2008)

Both of my Sierra diesel soundtraxx boards are tied directly to the track without a diode bridge. And just yesterday I had a third on my bench (steam version) and it worked directly from track power in both directions, and I ran it up to 20 volts.


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## Greg Elmassian (Jan 3, 2008)

Dan, you must have a full wave bridge between the board and the track somewhere, the board is definitely polarity sensitive.

Greg


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## East Broad Top (Dec 29, 2007)

In a track-powered installation (no 3rd-party control like Revolution, etc), the only connection from the track goes into terminals 7 and 8. That is not polarity sensitive. The Sierra reads the polarity of that in order to give directional whistles if you have the board programmed for that. Putting a bridge rectifier on that defeats that function. Battery power to the board (terminals 2 and 4) _is_ polarity sensitive. In a track-powered environment, you have the back-up battery connected to this in order to supply power to the board when the track voltage is low. There is no direct connection of track power to these terminals. 

In a 3rd-party control installation (constant track power or battery power to on-board speed controller) you would feed the power from the battery into terminals 2 and 4. If you're using constant track as a power source, you would need a bridge rectifier on those inputs. Pins 7 and 8 would be connected to the motor output of the ESC. Note that with some 3rd-party controllers, you would need an opto-isolator between the motor output of the ESC and pins 7 and 8 (as illustrated in the diagram above). Otherwise, the board thinks it's getting full power and you do not get any of the idle sounds like Fireman Fred, nor can you get any directional sounds. I _think _on the diesel, the prime mover sound ramps up to full power, but I can't remember if the prime mover is tied to motor voltage or wheel rotation. 

Later,

K


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## Greg Elmassian (Jan 3, 2008)

Kevin is right, had to search the manual to see the right track power setup, and indeed the 7 and 8 inputs are not polarity sensitive. Therefore no power connection to 1, and thus no FW bridge.

Thanks for the correction Kevin

Greg


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## TonyWalsham (Jan 2, 2008)

Sierra sound is designed for filtered DC track powered locos and they worked really well.
However, what the Sierra cannot do is read pwm output from a battery ESC.
An opto-coupler pcb is required. Sierra published just such a circuit and I sold hundreds of them when Sierra was being made. They are no longer available.
Kevin. 
If an opto-coupler pcb was not used with *a battery R/C ESC*, as you said, a diesel sound would ramp up to full speed and stay there. There would be no at idle effects.
Likewise, a steam one set up with a mechanical chuff timer would do the same. Although the chuff would work as normal. Once again there would be no at idle effects such as Fireman Fred, and brake pump.
However it does depend if there is a common (-) ground connection to the ESC traction battery. If the Sierra battery was left in the circuit and the Sierra was only powered by the ESC output, the Sierra behaved exactly as it would if being used with regular track power. i.e. an opto pcb was not necessary.


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## toddalin (Jan 4, 2008)

So...,

Why couldn't someone simply tie pins 7 and 8 _to the motor being controlled by whatever means_ with a non-polarized cap to smooth out the pulses, and tie some supercaps to where the battery would be connected to retain the idle characteristics???

This would alleviate the need for an opto-isolater.


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