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Is there a way to test a decoder without installing it in a loco

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Is there a way to test a decoder without installing it in a loco
Posted by John-NYBW on Saturday, May 23, 2020 7:37 AM

I have a dead loco. It has a factory installed decoder so it is not one I could have fried with a botched installation. I don't know if it is the decoder that is fried, if the electrical pick up is faulty or the motor is dead. If the decoder is still good, it would be a candidate to install in another DC loco conversion. I don't want to go to the trouble of soldering it if the decoder is fried. I was wondering if it could be wired directly to the programming track to see if it can at least be programmed and if that succeeds, test the output from the decoder with my multimeter. Am I missing something?

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Posted by peahrens on Saturday, May 23, 2020 8:07 AM

Try a google search.  I found another site where folks did that, with or without a resistor load on the motor leads.

Paul

Modeling HO with a transition era UP bent

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Posted by RR_Mel on Saturday, May 23, 2020 8:39 AM

Because of all my screwing around with remotoring and installing decoders I built up a tester for DCC.  It isn’t the way to go for a single check but if you are doing a lot of DCC installs it really helps.  I've used it for the last couple of years for quickie checks.  I wired all of my steam and most of my diesels with the NMRA 8 pin connectors and use an adapter from 8 pin NMRA to 9 pin JST connectors.

I can check decoders or locomotives easily by just plugging them in.

https://melvineperry.blogspot.com/p/blog-page_40.html


Mel



 
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I'm beginning to realize that aging is not for wimps.
 

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Posted by wvg_ca on Saturday, May 23, 2020 9:04 AM

it's best with a DCC decoder tester, if you have access to one ..

failing that, it can be hooked to the track itself, and with a motor or resistor load for programming and reading CVs, two to the track, two to the motor or resistor, and then leads for the lights ..

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Posted by John-NYBW on Saturday, May 23, 2020 9:16 AM

I admit to being in the dark when it comes to electronics. I'm trying to understand the need for resistors. When I put a loco on my programming track, the power passes from the rails to the wheels to a wire connected to the decoder. Is there a reason I can't just bypass the wheels and wire the programming track rails directly to the decoder?

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Posted by Attuvian on Saturday, May 23, 2020 9:43 AM

John-NYBW

I admit to being in the dark when it comes to electronics. I'm trying to understand the need for resistors. When I put a loco on my programming track, the power passes from the rails to the wheels to a wire connected to the decoder. Is there a reason I can't just bypass the wheels and wire the programming track rails directly to the decoder?

 
John,
 
This is easily an over-simplified answer, but virtually all electronic components and assemblies operate properly with a "load", something upon which those electrons or signals are acting.  In our hobby that load is generally things like motors, lights, switches, actuators, etc.  To properly test something a resistor of an appropriate size is often substituted for the load that has been disconnected, in your case the motor and lights of possibly dead loco.
 
In your case, what does "dead" mean?  No motor movement or hum?  No lights?  Likely nothing at all?  There could be a number of things other than a bad decoder that could cause these symptoms.  Those other possibilities ought to be eliminated before chucking what may be a good decoder.  More detailed suggestions are sure to follow from other forum participants.
 
John
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Posted by wvg_ca on Saturday, May 23, 2020 9:54 AM

John-NYBW

I admit to being in the dark when it comes to electronics. I'm trying to understand the need for resistors. When I put a loco on my programming track, the power passes from the rails to the wheels to a wire connected to the decoder. Is there a reason I can't just bypass the wheels and wire the programming track rails directly to the decoder?

you can wire the decoder direct to the track, the resistor [or motor] goes to  different set of wires,, the decoder needs a load to read and write CVs

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Posted by tstage on Saturday, May 23, 2020 10:02 AM

John,

First question: What is the make & model of the locomotive?

I ask because if it has a QSI decoder, it's possible that the decoder was put in full "sleep mode", which will make it appear as if it's dead.  By double-pressing F6 quickly, it will gradually wake up the decoder.  If it is in full sleep mode, it will require double-pressing F6 3x - with a short 2-3 sec delay between each double-pressing.

Tom

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Posted by rrinker on Saturday, May 23, 2020 10:08 AM

 You can certainly run clip leads to the track inputs of the decoder, and measure the across the motor outputs with a meter. Just don't short the probes on the motor output, or the decoder WILL be fried if it wasn't before. 

 Do NOT ever connect power to the motor leads with the decoder installed and connected, that too will instantly fry the decoder. If you want to test the motor, make sure the decoder is disconnected from the motor and you can apply DC to the motor to see if it turns.

Even if the motor output is fried on the decoder, the lights should work - if you can turn the headlight on and off but the motor won't turn, it could be the motor drive or the motor itself, or maybe the gears are jammed (raspberry, if Lone Starr has been in the area). If the motor works but the lights won't go on, if they are LED, then the function outputs are most likely fried unless there's a loose wire. If they are incanfescent bulbs, they could be burned out.

                                    --Randy

 


Modeling the Reading Railroad in the 1950's

 

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Posted by betamax on Saturday, May 23, 2020 10:20 AM

Yes, there are decoder testers available, which can safely test and program a decoder.

ESU is one manufacturer of such a device. You can also use a Digitrax LT1. Other sources include NCE and Zimo. The better ones have multiple interfaces that can accomodate almost any decoder made today.

 

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Posted by selector on Saturday, May 23, 2020 10:25 AM

I reset a QSI decoder using Paged Mode because it wouldn't respond in OPS mode, using my DB150.  It lurched each time I input one of the three CV changes required by a QSI.  That told me it wasn't a bad motor or motor output.  When I input the final CV change, the decoder lurched, the track power went dead as always happens in Paged Mode with the Digitrax DB150, and when I restored power to the rails and acquired Add "03", the loco control was restored to me.

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Posted by John-NYBW on Saturday, May 23, 2020 10:43 AM

tstage

John,

First question: What is the make & model of the locomotive?

I ask because if it has a QSI decoder, it's possible that the decoder was put in full "sleep mode", which will make it appear as if it's dead.  By double-pressing F6 quickly, it will gradually wake up the decoder.  If it is in full sleep mode, it will require double-pressing F6 3x - with a short 2-3 sec delay between each double-pressing.

Tom

 

It's an Athearn RS1 with a non-sound Digitrax DH123 decoder. I have several old DC diesels that I could repurpose this decoder for if it is still alive. Steamers need sound but I can live without it in my diesels. I even have an old doodlebug I'd like to put inservice on my branchline. 

PS. For those who have suggested a decoder tester, it doesn't seem cost effective to me. This could be a one and done operation and the decoder I'd be saving is probably one third the cost of a decoder tester.

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Posted by betamax on Saturday, May 23, 2020 11:27 AM

If it was an expensive sound decoder, yes, a decoder tester would be a good investment. But for a simple, cheap decoder, not so much. If it is a low cost decoder, just replacing it would be a better choice, and you can always mess with the old decoder later.

Ensure the wiring is correct before installing a new decoder, and use the program track to determine if there is an issue before giving it full power.

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Posted by tstage on Saturday, May 23, 2020 11:30 AM

John-NYBW
PS. For those who have suggested a decoder tester, it doesn't seem cost effective to me. This could be a one and done operation and the decoder I'd be saving is probably one third the cost of a decoder tester.

True.  But if you will be doing other installs in the future and want to test a decoder before installing it to make sure that it's working properly - especially if it's a used decoder, a decoder tester might be worth the investment and end up saving you a lot of grief and head-scratching in the long run.

Tom

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Posted by MisterBeasley on Saturday, May 23, 2020 12:29 PM

I'm not sure how a Digitrax programming track responds, but as I recall if you try to program a locomotive without a load on the motor outputs, you will get an error code.  Have you tried just putting this engine on the programming track and reading the address?  If you get any response at all, it tells you the decoder is getting track power.

If this is a basic wire-in decoder, not a plug in, you can use clip leads to connect it to power and use about a 75 ohm resistor for a motor load.  With power and a motor load, you should be able to read the decoder and change CVs.

It takes an iron man to play with a toy iron horse. 

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Posted by UpNorth on Wednesday, May 27, 2020 9:01 PM

If you have a Digitrax DCC System, it came with the LT1 that doubles as a decoder tester and a Loconet cable tester. The setup instructions are available from Digitrax web site.  Dirt simple to use.

https://www.digitrax.com/media/apps/products/accessories/lt1/documents/LT1.pdf

Marc

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Posted by John-NYBW on Thursday, May 28, 2020 7:04 AM

UpNorth

If you have a Digitrax DCC System, it came with the LT1 that doubles as a decoder tester and a Loconet cable tester. The setup instructions are available from Digitrax web site.  Dirt simple to use.

https://www.digitrax.com/media/apps/products/accessories/lt1/documents/LT1.pdf

Marc

 

I have a number of Digitrax decoders but my system is a Lenz. I don't recall seeing anything in the manual that describes something similar but I'll go back and see if I can find something. 

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Posted by John-NYBW on Thursday, May 28, 2020 7:15 AM

MisterBeasley

I'm not sure how a Digitrax programming track responds, but as I recall if you try to program a locomotive without a load on the motor outputs, you will get an error code.  Have you tried just putting this engine on the programming track and reading the address?  If you get any response at all, it tells you the decoder is getting track power.

If this is a basic wire-in decoder, not a plug in, you can use clip leads to connect it to power and use about a 75 ohm resistor for a motor load.  With power and a motor load, you should be able to read the decoder and change CVs.

 

It is an Athearn RS3 loco with a factory installed Digitrax DH123 decoded with a 9 pin JST harness that is connected to a circuit board. I'm guessing the circuit board is what Athearn used on the DC version of the loco and they simply attached the decoder to it. The loco is dead but it could be the decoder, the DC circuit board, or the motor. If the decoder is still good, I have several DC locos I could switch it to and then replace the DC circuit board in the Athearn with a TCS A4X or similar decoder. Given my less than stellar soldering skills, I would rather not go to the trouble of soldering the DH123 to a new loco without knowing first whether it is any good.  

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Posted by rrinker on Thursday, May 28, 2020 7:35 AM

 Those Athearn RS3's are notorious for bad pickup. I went through 2 to get one working one. Nothing was soldered - the loco comes with a 9 pin connector to just plug the decoder in. Part of the problem is the little plastic clips holding the wires on, another problem is that the black wire is supplied by a short piece of wire with a ring terminal on it that gets trapped between the board and the loco chassis by one of the screws holding the board in place. The final issue is that unlike the old BB locos it is based on, the added a black plastic piece that hides the shiny sides of the truck frames, and on ly first one, the slots in the plastic for the axles is not deep enough so the loco rides on the plastic instead of on the little square bushings which conduct electricity from the wheels and axles to the truck frames.

If the black wire which loos up from under the corner of the board is missing, you have no pickup on one side. If it's there, try powering the loco with clip leads, on to the terminal this black wire connects to, and one to where either of the wires from the trucks connects (on the board, the terminal in front is connected to the terminal in back with a trace, so it doesn't matter which end you connect the power. Bet it will work. It's really not that easy to fry a decoder, not when there is a provided plug.

 What's the road number? If it's 100-127, it's very likely programmed as SHORT address 100-127 if the previous owner had Digitrax. Lenz requires anything over 99 to be a LONG address. 

                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by richg1998 on Thursday, May 28, 2020 11:43 AM

Very easy to build a decoder tester. I did about ten years ago using an extra can motor with a flywheel on it with stipes drawn on it to get an idea of motor response.

Green LED for forward with 1k resistor and red LED and 1k resistor for reverse all on a plastic box. You can add to it if decoder has more functions.

I used what I call flea clips to connect the decoder. Better than alligator clips. Worked very will.

You cab use the varius connectors.

I think commercial versions are sold.

A Google search would have solved this question much quicker.

Rich

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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Posted by John-NYBW on Thursday, May 28, 2020 7:39 PM

rrinker

 Those Athearn RS3's are notorious for bad pickup. I went through 2 to get one working one. Nothing was soldered - the loco comes with a 9 pin connector to just plug the decoder in. Part of the problem is the little plastic clips holding the wires on, another problem is that the black wire is supplied by a short piece of wire with a ring terminal on it that gets trapped between the board and the loco chassis by one of the screws holding the board in place. The final issue is that unlike the old BB locos it is based on, the added a black plastic piece that hides the shiny sides of the truck frames, and on ly first one, the slots in the plastic for the axles is not deep enough so the loco rides on the plastic instead of on the little square bushings which conduct electricity from the wheels and axles to the truck frames.

If the black wire which loos up from under the corner of the board is missing, you have no pickup on one side. If it's there, try powering the loco with clip leads, on to the terminal this black wire connects to, and one to where either of the wires from the trucks connects (on the board, the terminal in front is connected to the terminal in back with a trace, so it doesn't matter which end you connect the power. Bet it will work. It's really not that easy to fry a decoder, not when there is a provided plug.

I must be an exceptional klutz because I have managed to fry three of them in the past month, the last one being the same kind of DH123 with the 9 pint JST connector. I was trying to hook it to a Walthers doodlebug which is a piece of junk and probably not worth the effort. It uses a belt drive and the belt tends to slip resulting in the bug moving in a herky jerky fashion. I'm looking at some of my real old locos to see if there is a motor I could cannibalize and put in this. I think Walthers only offered that for a few years and it is easy to see why. There aren't a lot of choices in doodlebugs and I wanted that one for my branchline because it is short and a better fit for the tight curves I have on my branchline. 

rrinker

 What's the road number? If it's 100-127, it's very likely programmed as SHORT address 100-127 if the previous owner had Digitrax. Lenz requires anything over 99 to be a LONG address. 

                           

 

 

The one that went dead is a NYC and I can't remember the number off hand but I'm pretty sure it is four digits. I have two others that are still operational. They are Rio Grande nos. 5200 and 5202. Not positive about the second number because I just repainted them and am in the process of decaling them for my fictional road. I was going to assign them numbers in the 600 series. 

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Posted by UpNorth on Thursday, May 28, 2020 7:59 PM

" I have a number of Digitrax decoders but my system is a Lenz. I don't recall seeing anything in the manual that describes something similar but I'll go back and see if I can find something.  "

Don't bother.  The LT-1 came with all Digitrax Command Stations, not the decoders.  If you do not have a Digitrax Command Station, you won't have an LT-1 hanging around.

Marc

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Posted by betamax on Friday, May 29, 2020 7:05 AM

UpNorth

" I have a number of Digitrax decoders but my system is a Lenz. I don't recall seeing anything in the manual that describes something similar but I'll go back and see if I can find something.  "

Don't bother.  The LT-1 came with all Digitrax Command Stations, not the decoders.  If you do not have a Digitrax Command Station, you won't have an LT-1 hanging around.

Marc

 

As Digitrax shows it with an MSRP of $5, you can probably buy an LT1 at the hobby shop, or they can order one.

The DCCWiki's Decoder Tester page has a video that demonstrates how to use an LT1 to test a decoder.  It is rather rudimentary compared to a more sophisticated unit, but it will tell you if the decoder is working. You won't know if the motor drivers have been damaged or destroyed though.

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Posted by rrinker on Friday, May 29, 2020 7:38 AM

 Sure it will. When you hook up the LT1 to use as a decoder tester, it goes on the orange and grey wires. Depending on the direction one or the other LEDs will light up and should change in brightness as the speed increases.

 In fact that's ALL it tests, it doesn't test the function outputs for lights.

 Not sure how a decoder gets fried just plugging it in when there's a 9 pin socket to use. Not too many with a 9 pin connection are of the type where certain traces on the factory board need to be cut. You find that on locos with 8 pin connectors - the instructions must be checked, or look for installation pictures on the TCS site, it doesn't matter that you are not using a TCS decoder, the connections for all decoders are the same. 

 Kenz has been known for running rather high on the output voltage tot he track, perhaps there are peaks exceeding 20 volts, though you won;t be able to measure those with even the rrampmeter. And most multimeters good enough to have a truly usable peak hold will also be TrueRMS, meaning they can compensate for a square wave, but will not be reliable at the DCC frequency and the reading will be off. I'd be very concerned with my wiring and the rest of the system if decoders are frequently failing. I've got some that have run hours and hours continuously at club shows and they are in no way degraded from ones that only have a few spins around my old layout. And the club layout is pretty large, with at least 5 boosters spaced out around it. An occasional DOA fresh out of the package is possible, but I haven't even had one of those. For them to keep failing while in use indicates something is wrong.

                                                --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by UpNorth on Friday, May 29, 2020 9:40 PM

Read the instructions.

It can be used to verify, motor, direction and and function outputs.

Just disconnect the motor leads and connect the blue common and one output.

Simple and to the point.   

Marc

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Posted by richg1998 on Sunday, May 31, 2020 6:25 PM

I did forget to mention about a decoder tester, I had an inexpensive Vellenmen digital O scope which would tell me the DCC voltage so I new the DCC P to Peak voltage. The scope had a test point for calibration. Nice. Simple math gave me the RMS which closely matched my Harbor Freight multi meters.

I think it converted to RMS. I have since given it away as I not longer model DCC. Eyes and hands.

You can buy add on's cheap enough today. Google should be your best friend,

 

Rich

 

If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.

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