# LGB chuff on LGB Sumpter Valley loco works in one direction only



## trainhead (Jul 29, 2010)

On an LGB Sumpter Valley mallet loco, the analog sound system seems to be working except that the 'chuff' only works when the locomotive is in reverse. The 'startup sounds' (whistle, bell) also work only when backing. Background sounds come out okay in either direction. Any suggestions as to what's gone wrong? This locomotive uses a ferrite disc mounted on the 6th axle as a sensor. The sound system is completely self-contained in the locomotive - nothing in the tender. Suggestions? Thanks.


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## Cougar Rock Rail (Jan 2, 2008)

Hold old/worn is the loco? It's possible that when the engine goes forward, the worm gear 'forces' over the drive axle enough to move the ferrite wheel away from the sensor just far enough that it doesn't pick up. Try putting the loco on it's back, clip some alligator clips on the sliders, put on some power to make the wheels go forward, then into reverse, and see if the axle does a little sideshift. If it does, put it back into forward and try putting a little side pressure on the axle and see if that moves it enough for the chuff sensor to work. If that fixes it, then you need to figure out a way to shim the axle so it doesn't move so much. I can't think of any other reason it would only work in reverse. 

Keith


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## TonyWalsham (Jan 2, 2008)

Has this just happened when it was working OK previously? 

Have you changed power supplies/controller? 

Is the power supply/controller Linear or PWM?


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## trainhead (Jul 29, 2010)

Hold old/worn is the loco? 

Not much wear, but I will check the end-play issue. The ferrite (or fiber?) disc floats on the 6th axle - it moves back and forth freely. It turns in a slot which is part of the sensor unit. Even if there were excessive end-play on the axle, the disc should stay where it belongs. 

Has this just happened when it was working OK previously? 

It worked previously. I've been testing it with a MRC Tech III. The power supply to the track is linear but that really shouldn't matter since LGB has a rather elaborate power supply inside the locomotive and the sound card is powered from that. 

My puzzle is why it works in one direction and not the other. 

There is a 3-conductor wire running from the sensor unit to a connector on the LGB sound card. Any guesses as to what the wires do? (Power, ground, sense? Common, forward, reverse? I'm just guessing). If so, a broken wire/bad connection is a possible answer. 
To state the problem another way, the sound system senses that the locomotive is going in reverse (and then various sounds happen). But when the locomotive goes forward, the sound system does not sense this - nothing. nada - it continues to behave as if the loco was standing still.


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## TonyWalsham (Jan 2, 2008)

LGB say their sound equipped locos should only ever be run on Filtered Linear DC. 
Are you sure the MRC Tech III complies with that requirement? 
Any sort of pulse or PWM output could "confuse" the LGB electronics.


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## Greg Elmassian (Jan 3, 2008)

I agree, we just had another thread where there was a decoder in the LGB loco that produced strange results. 

I believe the Tech III has pulse power of some sorts at low voltages and it cannot be turned off. 

Regards, Greg


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## trainhead (Jul 29, 2010)

Hold old/worn is the loco? 

Not worn. I checked the end play / side play and it's fine. While I was at it, I cleaned the chuff sensor and disk with a q-tip and alcohol. No improvement. 

LGB say their sound equipped locos should only ever be run on Filtered Linear DC 

Perhaps, but but I don't thing this is the problem. I tried running this on two different (ancient) HO power packs - clearly not pulsed. Same results. BTW, the locomotive runs fine (physical movement). 

I tried another chuff sensor (known-good) - no improvement. 

I re-did the IDC connection on the chuff sensor cable - no improvement. 

I did one more test: I put a couple of LGB track magnets on the track (to make the whistle blow / bell ring). They worked fine when backing (whistles / bell rings). They did not work at all going forward. LGB's logic seems to be that these magnets should not work (don't blow/ don't ring) if the locomotive is sitting still. But when this loco is going forward, the 'brain' thinks it's sitting still. 

There is either a logic problem (unlikely) or the sound board is simply not 'getting the word' when the engine is moving forward.


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## Cougar Rock Rail (Jan 2, 2008)

I would call Klaus at Massoth, I bet he will be able to help you out. 

Look here under 'contact': 

http://www.massoth.com/index.en.html 

Keith


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## Madstang (Jan 4, 2008)

Do you run MTS with a central station? 
If so try relinking the loco with the central station. Maybe the electronics got confused, as we all know electronical components do get OR loose something once and a while. 
What I don't get is the magnet. 
LGB uses the same system as Aristocraft to trigger the chuffs it is not the same set up as a Phoenix chuff sensor it has 3 wires as you have mentioned I would also like to know what they are for. I am a little confused what the magnet is for as LGB's is contained inside the motor block. 

Again Kluass is a great source. 
I will like to know what is going on also as I have never had that problem with mine.


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## Dan Pierce (Jan 2, 2008)

I can tell all of you that the LGB digital sound units with a hall effect axle sensor will not ring the bell or blow the whistle from the reed switch unless movement is sensed. 
This is true of my Digital mogul, mallet. and F7B units. Also, true on other engines I have serviced at Train-Li. 

The 3 wires from the chuff sensor have a power/ground/sense line and all 3 must be intact for the chuff to work. I fail to understand why direction causes a problem from the sensors, but i would understand if on analog tack power you have an issue due to an open diode for track power on the sound board. 1 open diode on a bridge circuit would cause the symptoms discussed here, except the writer states the back ground noises are there in both directions. Is it possible that there are 2 separate bridge circuits in the unit. I would like the part number of the loco to ascertain the sound unit type as I believe the mallet had 2 different sound models. I have the newer digital version with MTS.


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## Bill Swindell (Jan 2, 2008)

As I recall, that engine has the chuff sensor mounted to the left side of the engine block, right above the rear axle. Is it possible that the sensor has moved away from the magnets on the axle? Also, I have seen the axle magnet assembly split in half. That could mess things up. Please check the condition of the magnet assembly and the positioning of the sensor assembly.


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## trainhead (Jul 29, 2010)

A few quick comments plus a 'thousand words: 

First, there is no DCC, MTS, MTH, TE Revolution or anything else installed. It's pretty much stock. 

the chuff sensor is mounted to the left side of the engine block

Yes, that's where it is located. It appears to be in good shape. Ditto for the small ferrite/fiber disc mounted on the axle. The actual position of the sensor is pretty much fixed - slight vertical movement possible - maybe 1/16" max. But if it were displaced enough so as not to work, then why would it work in one direction?

The 3 wires from the chuff sensor have a power/ground/sense line and all 3 must be intact for the chuff to work.

Checked and re-checked.


I fail to understand why direction causes a problem from the sensors, but i would understand if on analog tack power you have an issue due to an open diode for track power on the sound board. 1 open diode on a bridge circuit would cause the symptoms discussed here, except the writer states the back ground noises are there in both directions. 

The background noises in the forward direction might just be the output of the capacitors. I probably should have tested it for an extended period of time.


The suggestion of an open diode makes sense to me. Or, it could be a cold solder joint on a diode that got a little 'colder' from handling. The problem was first noticed after handling the sound board (actually disassembling the whole banana).

A pic of the sound card follows. A small part of the card at the left of the pic is obscured by the boiler control panel, which was still installed.













A higher res pic can be found at http://daveh.ath.cx/sumpter_sound_card_4.jpg

Does anyone know the location of the diode(s) for track power? An open diode should be easy enough to test.












http://daveh.ath.cx/sumpter_sound_card_4_small.jpg














http://daveh.ath.cx/sumpter_sound_card_4_small.jpg


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## Cougar Rock Rail (Jan 2, 2008)

Yes, that's where it is located. It appears to be in good shape. Ditto for the small ferrite/fiber disc mounted on the axle. The actual position of the sensor is pretty much fixed - slight vertical movement possible - maybe 1/16" max. But if it were displaced enough so as not to work, then why would it work in one direction? 


If the axle was sideshifting then it would only work in one direction, which is why I asked you to go through the procedure mentioned in my earlier post. It doesn't take much to cause a problem. It's unlikely, but it is a possibility that you need to eliminate. Have you called Klaus yet?  

Keith


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## trainhead (Jul 29, 2010)

It's possible that when the engine goes forward, the worm gear 'forces' over the drive axle enough to move the ferrite wheel away from the sensor just far enough that it doesn't pick up. Try putting the loco on it's back, clip some alligator clips on the sliders, put on some power to make the wheels go forward, then into reverse, and see if the axle does a little sideshift.

No side shift that I could notice. The rear axle is at least as tight as the 1st and 2nd - maybe tighter.


With the engine inverted and supported and power applied to the wheels, I could get the 'chuff' (and start-up sounds) to work in reverse. It did not work with the wheels going forward. I tried moving the rear axle (the one with the sensor) from side-to-side and also putting some angular pressure on the axle while the wheels were turning. It did not make any difference in the result - chuff (and start-up sounds) worked in reverse; did not work going forward. My efforts did not cause more (new) problems, but did not solve any either. 
Earlier, I inspected the axle, fiber/ferrite disk and sensor housing from the top (with engine block top cover removed) but axles in place and supported from below. The disk moves quite freely but without slop on the axle. It was a good fit in the plastic sensor housing - not much slop there either.



From another message:

the writer states the background noises are there in both directions

The writer miss-spoke. The background noises last a few seconds (until the capacitors run dry?) and then stop. The writer needs a longer test track or longer work bench or both.


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## TonyWalsham (Jan 2, 2008)

Have you tried the loco with a true linear output controller with no pulse or pwm at all?


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## trainhead (Jul 29, 2010)

Have you tried the loco with a true linear output controller with no pulse or pwm at all?

It worked fine before with the MRC Tech III - worked in both directions of travel. Several other LGB locos with LGB sound cards work fine with that power supply (in both directions of travel). It worked fine (in reverse - but not going forward) with an el-cheapo starter-set power supply. I simply don't think the power supply is the issue.


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## gtrainman (Jan 5, 2008)

{el-cheapo starter-set power supply. } 

What brand/make of power supply? 

Also, I don't recall reading which version of the SV Mallet you have? 

What's the SV Mallet model numbers? 

(the were at least 4 runs/versions of the SV Mallets that I am aware of) 

Does it have a gray or black smoke box front on the boiler? 

BTW, Just a note here, none of the SV Mallet came with nor have track power pick up shoes on them.


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## Trains West (Oct 4, 2008)

though the mrc is pulse power i have used one for years without much problem 

if in dought with pulse power test wit a 9 volt battery 


in the picture the full wave bridge is here and the soder pads do not look great you need to take a good look at them



[url="


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## Greg Elmassian (Jan 3, 2008)

I was just about to post that too, sure looks suspicious. 

Greg


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## gtrainman (Jan 5, 2008)

I thought that the actual solder joints are on the other side/back/bottom of the board.
Those diodes look fine to me in that photo. Most of the diodes that I've seen go bad were popped as in exploded.

However, Internet repairs are really nothing but mostly guess work.


PS,
Trainhead,
what happens to the headlight on the loco and tender, are they on, off, on one way and off backing, is the tender light on when going in reverse ???

Are you running the loco by it's self or with the tender pluged in ?


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## Greg Elmassian (Jan 3, 2008)

If you look at the right most 2 diodes, it looks like there is a conductor between them, but it could be the picture and reflections. 

Regards, Greg


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## trainhead (Jul 29, 2010)

Problem solved. Thank you to everyone who responded. 

The problem was not a bad diode or anything like that. I did inspect the diodes as well as other components on the sound card carefully and under magnification. The only "issue" with the sound card that I could discover was a sloppy abundance of solder paste and flux on the card - easily remedied with a toothbrush and alcohol. 

The problem turned out to be an unexpected current path between the sound card and the power supply card by way of the boiler weights. Inside the Sumpter Valley mallet (LGB #20892) are two printed circuit boards. The front printed circuit board is essentially a power supply mounted by 4 screws threaded into the front boiler weight. 

The rear printed circuit board is the sound card, also mounted by 4 screws - 2 into the rear boiler weight plus 2 smaller screws that thread into plastic bosses molded into the bottom of the plastic boiler casting. Note that the rear-most 2 screws on both PCBs do not make any electrical connection with the PCB - they are simply there for support - no need for insulation or isolation (or consolation). 

On both printed boards, the forward-most 2 screws also serve to connect the heat-sink tabs of a solid state component (looks like a bridge rectifier) to their respective boiler weight - these heat-sink tabs ARE the front mounting holes. Therein the problem. Although the #20892 boiler weight is divided into 2 parts which are not connected, the gap between the parts is quite small. If oil or crud or foreign matter (Chinese delicacies?) builds up in the gap between the 2 halves of the boiler weight, a current path can form. If this happens, the symptoms originally complained of will occur (no chuff or "start-up sounds" in forward direction). This problem is easily demonstrated by temporarily bridging the 2 boiler weights. I discovered that this also adversely effects the physical running on the locomotive in the forward direction. That is, a locomotive suffering from "current path syndrome" runs MUCH BETTER in reverse than it does going forward. I can only speculate as to the havoc this unexpected current path would have on a DCC or similar control module. 

The fix is simple - be 100% certain that there is no possible current path between the power supply PCB and the sound card PCB, except for the 6--conductor cable connection intended by LGB. There are a variety of ways to achieve this, depending on the tools and materials available. Of course, start by cleaning out the crud. 

N.B. Everything described above (and below) refers to the first run of #20892 locomotives. They have white window frames in the loco cab and silver piping along the boiler. There was a later run of this locomotive which had red window frames and black piping. The sound card PCB in this latter run was much smaller in size and does not have the 'gold embossed' LGB logo. There may be been changes in the power supply PCB as well. 

Back to the problem, my good-for-a-thousand-years fix is to remove both boiler weights. Drill and tap the 2 forward PCB mounting holes in each boiler weight to 6-32. On re-assembly, put a fiber washer under the heat-sink tabs and use nylon 6-32 screws to mount the front end of both PCBs. The result is total electrical isolation. The 6-32 nylon screws should be readily available from any electrical supply, Home Depot, etc. They're used by some electricians to mount wall switch plates - perhaps because they don't rust in acidic environments. 

You could achieve the same result by using fiber washers above and below the heat-sink tabs, and plastic insulation around the original LGB screws. There's not much 'meat' in the heat-sink tabs so you may not be able to open this hole and fitting an insulator could prove tricky. 

Again, thanks to all who responded. It's been an adventure.


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