Testing old decoders

[rrinker]

 A lot of those old MRC decoders don;t have readback. Nor do they have a reset, so you may have to do some bling programming to get the decoder to a known address. If it won;t take an address on the program track, hook it to the main track (not they layout - you don;t want to accidently program all your locos) and program on the main to address 0 and set CV1 to 5 and CV29 to 6. Now test operation using address 3.

                       --Randy

[mfm37]

You should not need a load on the motor orange and Grey wires to test but a 12- 16 volt grain of wheat lamp makes a nice test indicator. comnnect it between grey and orange. If you have another lamp or lamps, you can connect one between the blue wire and each of the function wires. Make sure all connections are isolated from each other because any short between them will most likely6 destroy the function or motor control.

Now go ahead and connect the red and black wires to your track. To be really safe add a 100 ohm 1/2 watt resistor in series to one of the track power wires. That will limit current in case of a short. Most decoder testors have one built in. With the "light bulb" load you should bne able to program and read the decoder as well. The bulb on the motor leads will go from dim to bright as speed is increased.

Martin Myers

[richg1998]

You will need a motor or a 1/2 half watt, 100 ohm resistor. I have done both.

A load is usually necessary for the DCC controller to "see" the decoder. Your mileage may vary. I never tried MRC decoders.

I got this idea from the below site some time ago. Scroll down to using as a sound only decoder.

http://mrdccu.com/curriculum/soundtraxx/tsunami.html

 

Rich

[gmpullman]

It is possible that some decoders are looking for a load across the motor output leads. You might want to find a small 12V DC motor to use as a load. Check the current draw of the motor first to be sure it isn't consuming more than the rated capacity of the decoder.

Then you can read the voltage across the orange and gray wires with the motor running freely. With no load and only the meter you might get a higher voltage reading. The motor will also allow you to easily check forward and reverse functions.

I once tried to program a decoder with no load across the motor leads and it wouldn't work, I had to temporarily shunt a resistor across M+ and M—.

Just a thought...

Ed

[gregc]

bruce22

If I connect the red and black wires to my track, will I get any multimeter readings from the Orange- grey and other wires ?

if the decoder you have is similar to that shown below, then I would think that you should be able to see motor voltage vary across the orange/grey wires and voltage across the blue/white or blue/yel when on.

[RR_Mel]

Yes you can do that.  Blue is common to white and yellow for lighting.

 

I made me a DCC tester for checking decoders and locomotives.

 

http://melvineperry.blogspot.com/2014/09/september-17-2014-dcc-test-box.html

 

Mel

 

 

Modeling the early to mid 1950s SP in HO scale since 1951

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

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

[snjroy]

I'm no expert but i suspect yes if you have the right address on the dcc system with full throttle on.

[bruce22]

I have a few old Model Rectifier AD series decoders I would like to test to see if they still function. However I do not have a commercial tester. If I connect the red and black wires to my track, will I get any multimeter readings from the Orange- grey and other wires ? I operate with the Prodigy Express. Thanks.