I spent some time this evening, cleaning the brushes and commutator on the Scout 2-4-2. Put it on the track and hey presto, nothing. Not a thing. 

The KW transformer is humming, the red light isn’t on but checking with a multimeter, I get NIL output at the terminals or at the rails. This is completely new. 

Searching the forum, I find a similar query ending with the advice that “the circuit breaker is stuck open - close it and you will be fine”. Ok, I’ll go with that. I’ve been working through various old items and maybe I’ve tripped the circuit breaker. I know older Harleys and usually when the circuit breakers trip on those, leave ‘em a while and eventually they reset. 

I don’t take that to be the case here, from what I’ve read. I’ve found a service sheet for dismantling the case, which sounds straightforward enough, but what exactly am I looking for with the circuit breaker? 

Original Post

I have a schematic. It makes sense that it would be a circuit breaker trip, as there are no other symptoms and no output anywhere. 

My real question is, is this a “service” item or a simple manual reset of the existing unit? Will I need to replace it? If so I might as well order one now. I don’t like opening a casing and finding that I need parts I don’t have, I’d rather get all ready then open the case.

That’s about what I thought. I’ve had Sportsters for many years and it’s never wise to go anywhere without a couple of circuit breakers in your pocket... once in a while they just don’t reset. Eventually you have them all replaced with modern type ones and the problem goes away. 

There are plenty of people advertising conversions, so I suppose the older ones aren’t available any more, anyway I don’t like using old electrical parts. 

Ok, I’ll get on it. Plenty to do in the meanwhile. 

Ok good info all round, thanks all. 

I’m going away at the weekend for two weeks so I’ll order a breaker and do the whole job when I get back. Cars over here use fuses, not breakers and electronics shops are pretty much extinct, I’ll need to order one online.

ok, press on.


I second the 10A breaker, the KW is really only good for around 140-150 watts output.  Remember, PW transformers are rated on input power, so you need to cut that by about 15-20% to come up with output power.  Also, the maximum power out is only at full throttle, when running at half power, you don't get nearly full power.

Just a idea have you checked the solder joints ? I picked up a KW years ago for cheap as it had the same problem. Turned out to be a broken solder joint on the secondary coil.

One thing about trains, it doesn't matter where they are going, it's having the sense to get on.

The KW has a new power lead, fitted by the previous owner whose soldering was a lot better than mine, so I’m assuming that the solder joints are good. The symptoms certainly fit, for a failed circuit breaker. 

I found this page http://www.tranz4mr.com/KW_Re-Build.html which contains a lot of detail, and includes an external check for the binding posts, so I’ll do that this morning. I doubt that it’s a failed binding post, as all the terminals are equally affected. 

From experience of the circuit breakers on older Harleys, if it has an old-style mechanical breaker inside the case, it would be worth replacing it with a modern one anyway. I had already noticed an occasional hesitancy so my thoughts were already pointing in that direction. 

I was already thinking about trying one of the Harley circuit breakers, I have a couple of spares in hand but I don’t believe I have a 10A one. 

Anyway I now have a fairly complete check list and some good detail photos to work to, so I’ll order a new circuit breaker on general principles and make a start when it arrives. 

KW circuit breakers are notorious for falling apart. The older style Part 20-22 has layers held together by a rivet which comes apart after 40 years or so. Replace with part number 20-22R for about $8.50 plus shipping from most parts guys.  
Also look for loose wires on the circuit breaker, metal bracket that holds the whistle rectifier disk and as others posted loose wires on the back side of the terminals. 


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Actually Trainz4MR is correct, the early breakers literally fall apart. It is put together with a single rivet and the rivet edge burns off the same way the binding posts do, and no longer have the tension to operate. pieces are just dangling there. 20-22R is not an official number, that is Jeff Kane's number. The R is for reproduction.

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