# The optical sensor for the chuff in my Bachman K-27 seem to have quit



## jimtyp (Jan 2, 2008)

I've been using the optical sensors on my B' K-27 to feed the chuff trigger on my Phoenix P5 successfully for 6 months, however, the sensors seems to have quit. I say seems because I'm not 100% sure that is the problem. 

I swapped out the P5 with another and it doesn't chuff either. I verified the wires are still connected up properly to the circuit board in the tender. Everything on the sound card works but not the chuff. I hooked up a reed switch and magnet in place of the sensor jumpers and the chuff works.


So it seems that either the optical sensors have failed or a wire or circuit within the loco or tender has failed. The diagram shows 2 sensors and it seems unlikely they would both go out at the same time so it's probably something in the circuitry? If one sensor failed would it cause the other to fail also?


The problem occurred Sunday when I put the loco on the tracks and started it up. I run DCC. The loco started moving and the chuff was working, then the loco kind of sputtered, lurking forward, stopping and then forward again. At first I thought it was my power connection to the rail, but then discovered one of the big plugs between the loco and tender wasn't pushed in all the way. After I pushed in in tighter the loco ran fine but no more chuff.


Has anyone else had this issue?


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## Curmudgeon (Jan 11, 2008)

Without referring to my wiring diagram, possibilities include a failed ground with the plug not seated and subsequent fried circuitry. 

Without seeing it, hard to say exactly. 
Probably not the optics, rather the circuitry that drives them. 
If you want to lock 1 and 4 axles, I have a photo series somewhere on making a magnetic timer on #4 axle that works just fine. 

However, if you post this in the dcc forum, I am certain one official unofficial spokesperson will have all the answers you need.


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## jimtyp (Jan 2, 2008)

Thanks Dave! I saved the magnetic timer photo series info you posted earlier this year, just in case. If I can't get this resolved I'll go with that solution. 

I'll take the boiler off this weekend and see if I can see anything and try and trace things back along the wiring. If not I'll re-post this in the DCC forum.


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## StanleyAmes (Jan 3, 2008)

Jim

Its preety easy to isolate the problem. The most likely cause of the failure is the transistor you added to invert the chuff or a poor connection in the tender in the connection to the soind card.

To test the locomotive connect a volt meter between ground and the chuff pin. when you move the locomotive you should see a very short positive voltage.

To test the sound card connect a ground lead to the P5 chuff input. Each time you touch the trigger you should get a chuff.

You also need to ensure that you have a voltage between the locomotives + and - . ALl this can be easily be done in the tender.

Stan


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## jimtyp (Jan 2, 2008)

Thanks Stan! I did replace the transistor just in case. I hooked up the volt meter between J1-5 and J1-7, but see nothing when the loco is moving, that is no voltage. If I manually apply a 250ma charge to J1-5 (the chuff input) then I get a chuff. So the sound card is definitly good, and still looks like a wire, sensor or circuit issue. What would you recommend testing next? Do you know which wire on the plugs runs the chuff input from the loco to the tender?


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## SteveC (Jan 2, 2008)

Jim

Don't know if this will be of any help or you may already have them, but Bob Grosh did a couple of drawings which he posted in a previous topic.

*http://1stclass.mylargescale.com/bobgrosh/posts/k27/dwg/K27PG1large.jpg*

*http://1stclass.mylargescale.com/bobgrosh/posts/k27/dwg/K27PG3large.jpg*


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## jimtyp (Jan 2, 2008)

Thanks Steve! You are so organized! And thanks Bob for putting this together  This will help me trace the input back to the loco.


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