View single post by Reg H
 Posted: Thu Mar 5th, 2020 08:17 pm
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Reg H

Joined: Sun Oct 19th, 2014
Location: Shelton, USA
Posts: 1134
Hang in here as I temporarily change subjects.

I have been working on an Athearn "blue box" SW7. 
My first attempt ended in failure because I had neglected to check,
to see if the chosen decoder would fit in the locomotive. 
I had the decoder laying around.

I checked the Digitrax sizing app,
and they recommended the smallest decoder they make.  Wow. 
Anyway, after it arrived I determined it would fit
(I ended up mounting it on top of the front gear tower)
I did the install.

When I put it on the programming track it programmed perfectly. 
But it wouldn't run.  Just like the SW1200.

So I examined all the connections. 
I had determined that the locomotive ran fine before starting the conversion. 
I could find nothing wrong.

I ran a resistance check, between the motor frame and the chassis. 
Completely open !

Though I had tugged on the bottom motor connection, confirming it was firmly soldered,
I hadn't pulled the motor to look at it.  As a last resort, I did that.  Very firmly soldered. 
In fact, the wire was buried in a rather slovenly blob of solder.  

Upon close examination, it looked like that blob of solder, might be able to contact the frame. 
Without much hope that was the problem,
I applied some additional tape to the frame and reassembled everything. 
Well, at least the chassis. 
I wasn't about to finalize the install until I was sure it basically ran.

That bit of solder, had been defeating my efforts to isolate the motor.  

You know where my mind is going.  

Once I have the SW7 completed
(There are some minor issues.  Something is still rubbing on one of the flywheels)
I am going to take a VERY close look at the SW1200's motor isolation.  


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