Kato SD80Mac slow running

At a recent train show one of my buddies from the Ntrak club I belong to asked me to take a look one of his Kato SD80Mac locomotives.  His complaint was that while it did run, it was slower than other identical locomotives.  I verified this on my test layout and it seemed to get worse the more I ran the locomotive. I then took the shell off to test the motor for current flow and this is what I found.

Apologies for this blurry photo.

The kapton tape was coming into contact with a rotating part of the motor as indicated by the arrow on both sides preventing the motor from turning freely.  This put an overload on the decoders motor output.

This photo shows how the installation should look. The kapton tape comes over the side of the frame on each side and stops before reaching the open part of the motor.

This type of installation is common to several Kato models.  They are generally an easy DCC installation but it is a good practice to always check for free rotation of the motor when doing an install.

When I put the decoder on my test fixture, the voltage on the motor output of the decoder was zero when connected to the test motor but was normal with no load. There was no sign of anything burned on the decoder.  A reset was programmed into the decoder but this did not clear the problem.  In this case the decoder needed to be replaced.

Before installing the replacement decoder the current draw of the motor was measured by connecting the motor directly to my bench DC power supply as shown in this photo.  It is rare but I did once see a defective motor cause a decoder to burn out and that became the first post on this blog.

Kato E8A won't program

Not much new decoder installation material to report on lately but recently at a local show one of the guys in the Ntrak club was having trouble programming one of his Kato E8A's that he had just put a decoder in.  On our Digitrax system the throttle display indicated "NoPrG".

This photo shows the decoder installation. A visual inspection indicated that everything was done according to instructions.







What I found when I got this loco to my bench was that the motor contact strips were not making good contact with the board.  This is a common problem and I always solder the contact strips to the board.  What happens is that a current has to pass through the motor to complete programming.  That is why you may notice a loco move or feel a vibration when sending it a program.  On this type of mechanism the motor brush contact strips are held in place against the board by a plastic clip.  This clip by itself sometimes does not stay tightly in place.

This closeup shows how the motor contact strips are held against the board by the clips.  To solder the contacts in place, remove the clip and melt a small amount of solder to both the board and the bottom side of the contact at the end.  Then use a small screwdriver to hold the contact tight against the board while re-melting the solder making the bond. Care needs to be taken to avoid melting the kapton tape on the wheel pickup strips.



If soldering is not an option then I would suggest a thin piece of scotch tape be placed over the plastic clip and reaching the gray plastic motor saddle on both sides to help keep the clip from coming loose.

It is even possible that a loco could seem to run OK in DC or DCC and then show this same programming problem.   That is because the contact is not good enough to pass enough current to make the programming function work but enough current could flow to turn the motor.  I've also seen this happen a time or two on a wired decoder where the connection to one of the motor brush caps was just hanging by a few strands of the wire.

On this Kato E8 it is interesting to note that this particular mechanism was introduced by Kato in 1994 and was one of the first mechanisms designed to accept a board type decoder even though it would be a few years before such a decoder was available.  Since then several other models have be been introduced that use this same design on similar mechanisms.

A most unusual shorted axle

Yesterday I had received an N scale Precision Craft E8A that I had installed a decoder in about 2 years before that now shorted the DCC system whenever it was put on the track.

The Precision Craft E8 is designed like a scaled down HO engine because it uses wires from the trucks, motor, and LED headlight that all plug into a circuit board.  The board also has an 8 pin connector that either has a decoder or jumper wires if it has no decoder.  I recalled that what I had done was to cut the jumpers on the original plug and then to solder the wires of a DZ125 decoder to the pins.

Here is a stock picture of a decoder like so you can get an idea of what this looks like.



This plug arrangement came in handy when troubleshooting this problem as I did not even have to turn on the soldering iron.  After first verifying that the locomotive indeed did cause a short of the DCC system as soon as it was on the track, I began to unplug things.

• Unplugged the decoder, still got a short.
• Unplugged the motor, still got a short.
• Unplugged the rear truck, still got a short.
• Unplugged the front truck, still got a short.

At this point, I placed each truck on the track one at a time and discovered that the front truck was the source of the short.  Because all three axles are picking up power and are connected on each side by a metal side frame I took the truck apart to test each axle and find the one that was shorted. 

First I checked the wheel gauge with an NMRA N scale standards gauge and it was OK.  Then pulling the wheels out from each side I could see that the pins that come off the wheels and insert into the plastic tube part were long enough for the ends to touch inside the plastic tube part.  I then took a bit off the end of one of the axle of one of the wheels  with a Dermal tool cutoff wheel and that solved this problem.

Almost all N scale locomotive axle assemblies look like the photo at left.  Two solid metal wheels with metal axle pins that insert into the ends of a plastic tube that has a gear.

It is easy to see how this could happen on any locomotive when the total length of the two metal axle pins are longer than the length of the plastic tube.

I would suspect that this could happen after someone pressed the wheels together to correct the wheel gauge.  The owner of this engine said it started after the engine had derailed.  I suspect that the ends of the 2 axle pins were already very close to touching and getting bumped by the derailment was just enough to make them short.  This ended up being one of those very unusual problems that I though was worth sharing.  I was relieved that the problem had nothing to do with my workmanship and the owner of the locomotive was relieved that the decoder was not burned out.

First Post - That one in a thousand

A friend in Chicago who does his own installations called to tell me about a problem he was having with an engine that he had installed a decoder in several years ago and now was not working.  He had tried everything he knew how to do but was stuck.

So I had him send me his Kato U30C with a Digitrax DZ123 decoder.  When I got it I took the shell off and did a quick inspection of the installation.

• He had used an Aztec Trackmaster milled frame - OK
• The all of the wires appeared to have their insulation intact and not pinched anywhere - OK
• The motor turned freely when spun by the flywheels - OK
• The decoder was attached to the frame with a piece of double stick tape - OK

I then put it on the test track and sure enough, it would not respond to either DCC or DC.  I reset this decoder by programming 08 into CV 08. Then I got it to move on the default address of 03 but the LEDs were acting strange.  The rear LED was acting like a strobe when the engine was in reverse and the front LED was on all of the time.  I also noticed that this engine seemed to need a higher throttle setting than normal and I knew that the momentum settings were zeroed because I had reset the decoder.

Then I saw the smoke !



I immediately removed the loco mechanism from the track and removed the decoder from the double stick tape that secured it to the frame.  There was a burned spot on the bottom of the decoder.

As I had seen decoders burn out before, I thought that what it was a went about replacing the decoder.

In the course of doing this I had the mechanism completely apart and then back together again so I felt sure that everything was right.  This time before I put the wheels back on, I held the mechanism in my hand and placed each side of the frame on a rail.  I turned the throttle up and everything seemed OK, the motor ran and the LEDs responded as they should.  It was then that I noticed that the decoder was warmer than it should be.
 
I then decided to take a current reading on this motor.   I did this by placing my amp meter in series between the motor and a DC power pack.  I was surprised to see that this engine was drawing at least 400ma and up to over 1 amp when the throttle was advanced to near full.  Normal for an N scale Kato engine is between 200 and 300 milliamps. 



This ended up being a defective motor which over time, ruined the decoder.  As it turns freely, there must have been something wrong with the rotor windings.  This is not something that can be repaired and the motor must be replaced.  It must be really rare, that this happens as I have worked on many engines over the years and this is the first time I have seen this.  Replacement motors for Kato engines are generally available if you look around.  The motors are the same for almost all of the Kato engines but you may have to change the flywheels.