Mark, I could do that, but it only masks the problem. With a slow moving loco crossing over a dead frog, the loco could stall when the rear truck crosses the frog. I have a spare DA-SR decoder and I will swap it today for the bad decoder. I expect that will solve the problem for once and for all, but you never know.
Rich
[quote user=“maxman”]
Rich;
Do you have a meter? I have a DA-SR in front of me with no wires attached. The back of the decoder defines the right rail conections as the side of the decoder with the two motor connections. Obviously the other side of the decoder is where the left rail connects.
Disconnect the wires to the decoder.
With the meter set at an ohms value, connect one meter lead to the front right rail connection point and the other lead to the rear left rail connection point. Your meter should read zero ohms. This is as it should be because the front and rear connection points are connected on the back side of the decoder with a large connecting trace as Randy mentioned previously.
Now re-connect the meter leads to the left side connection points. You should again get zero ohms.
I also connected the meter to the left and right rail connection points on one end of the decoder. With the meter set at 20K ohms or less, I read an open circuit, meaning that there was sufficient resistance from the decoder components to show an open circuit. I did check across these same points with a higher resistance meter setting. With the meter reset to 200K ohms, I read 63 ohms from the left to right rail connections. I reconnected the meter to the terminals on the other end, and got basically the same values.
I believe that the only thing you can check on the decoder is the front to back continuity. If you have that, then in my opinion there is a decoder fault. What I can’t tell from looking at the decoder is how the board components connect to the two large traces. I would think that the two traces are the main connection points and everything is in series with them. But I suppose it is also possible that there is some sort of parallel circuit where there are duplicate connections from each of the traces so the there is redundancy in case one end or the other of t
Rich,
I’ve followed this thread from afar, thinking all the time that the problem MUST be the continuity between the wheels/pick up and the motor. I strongly felt that the decoder could not possibly be the problem as one truck was pulling power and it was transmitted to the motor.
HA, you proved (to me) that the decoder was in fault, something that just doesn’t make sense (I’m a DCC guy but not big on electronics) to me.
Throw that sucker out, and put in a new one!
ENJOY
Later today, I will swap the bad decoder for a spare good one.
Presumably, that will solve the problem.
If it does, I will send the faulty one to NCE and tell them what the problem is so they can repair or replace it and confirm that, indeed, the front terminals are not transferring power to the motor.
Rich
You just have to be careful to not apply power to an output of the decoder, like the motor terminals or the light terminals. Checking continuity from one front truck connection to the correpsonding one at the rear will not harm the decoder.
If you have continuity between each of the front power terminals and the corresponding one at the back, then I am puzzeled as to how the one side’s power gets tot he decoder and the other does not. One or both of those paths must be open to cause this issue.
It’s not a valid test with the wires all hooked up - the continuity is then through the rails. If all this time you were testing with the truck pickup wires still attached, no wonder the results were so confusing.
–Randy
Randy, be gentle, LOL, I told you that I was an electronics illiterate.
The real test, though, was when I wired the front pick up wires to the rear decoder terminals and the rear pick up wires to the front decoder terminals.
When I did that, the front trucks worked with the rear trucks off the rails as opposed to the original situation where the front trucks did not work with the rear trucks off the rails.
With the wires reversed as described, the rear trucks no longer worked. Unless I am badly mistaken, that tells me the front decoder terminals are not transferring power to the motor.
I, too, am puzzled by this occurrence. But, am I wrong in my test and in my conclusion?
Rich
I am going to call Larry at NCE today and discuss this issue with him.
Rich
Since you’ve already found that one end of the decoder is not supplying power and the other end is, why not install jumper wires like I suggested on page 2? If you would do that, the shell would be back on and all would be working.
Chuck, I could do that but aren’t I just masking the problem?
Besides, what good would a jumper do if power is not reaching the motor from the front terminal on the decoder?
Rich
Rich, it might be masking the problem, but it is a solution that works. What you need to do is, solder both right side truck wires together, and then the left together. Then branch off of that with a couple of wires and solder them to the truck inputs on the decoder that work. You will then have all wheel pickup and the decoder will get its power.
I hope that is clear! I have installed over 2000 decoders for myself and a couple of shops and have done this in the past. It does work.
Chuck, I agree with you. It does work, and I have done it on a couple of decoders myself.
I am reluctant to do it here because I am fed up with the decoder problems that I continue to have with the DA-SR decoders on this ABBA consist. I bought a set of four DA-SR decoders for these four locos back in 2004, and I have had periodic problems ever since, mostly with this exact issue. I have already replaced one of the DA-SR decoders, and this will be the second one. I have also had issues with the function outputs on these decoders.
Needless to say, I am not fond of the DA-SR decoder.
Rich
I called Larry at NCE to discuss the problem, and he agrees, based upon what I described to him, that there is a fault with the decoder.
He did confirm that the front and rear power taps are interconnected through traces on the circuit board.
However, he also indicated that a hairline crack in the trace could prevent power from reaching the motor.
I am going to send it in and have the boys at NCE take a look at it and see what the problem is and whether the decoder can be repaired or else replaced.
Rich
Wow, Rich! Sorry to hear about all of the problems. I think I might be ready to try another brand. At least you have a spare that you can install to get them back up and running while the other is being repaired.
Thanks, Chuck, and believe me when I say that I appreciate all of your advice.
I feel so much better now that I have a fully operative decoder in this loco. It has been a long and winding road, so to speak.
Rich
So, you replaced the decoder with a spare and it is now okay?
Earlier you indicated you were having this issue with three units. 2 B’s and an A. Initially I thought it was something common to the units. Now it is clear it is the decoder. I recently got two four packs of these decoders. Right out of the package I found 2 of the first 4 had this same problem.
So the other two decoders could also have this issue.
Because, my sense is that decoders are fragile I felt a means to test the decoder was needed for my install work. For this reason, I got a decoder tester to make sure I’m starting with a good decoder. It is an added expense, but if your going to do a number of installs it will save you from this kind of frustration. With this tool, I know it it doesn’t work after install, the problem lies with me.
Larry
Like I have said,times before,‘‘I don’t know nuttin’’.
Cheers, [D]
Old Man,Frank
You’re welcome, Rich. I only chime in when I feel I have something to contribute. Not much for rambling!
Oh geez, I forgot to post the final result. Sorry, I was up all night with a faulty sump pump in the midst of a 2.5 inch rainstorm. I am not thinking straight.
Yes, I had a spare DA-SR decoder, and I installed it in place of the faulty decoder. My Athearn Genesis F7B now runs like a charm, power from all four trucks being transferred to the motor. Turns out, the trucks were fine all along. The problem was the decoder.
I will send the faulty decoder back to NCE for repair, and Larry has promised to have either Matt or Mike report back to me on what was exactly wrong with the decoder, although Larry suspects a hairline crack in the trace on the decoder.
Rich
I am glad you got it fixed. And I have to say you did a good job of diagnosing the problem.[8D]