Thursday, November 1, 2012

Lenz Silver Mini in an Atlas Classic GP35

One of the Classic releases from Atlas were the GP35's that were closely based on the mechanism made for them by Kato several years earlier.  The Atlas Classic GP30 also uses the same mechanism as the one shown here.  At first glance this would seem like a straight forward replace the frame type of installation but as I discovered there are a few extra tricks that are worth covering.

If you look at the frames for the Kato made model and the Classic models made in China, they seem identical in every way.  They both even have the same part numbers on them and copyright Atlas 1992.

There is a critical difference and it's important not to get them mixed up.  The photo on the left shows the right side frames from each model.  The size of the bushings used on the Classic version are slightly smaller and where they fit in on the frame is also slightly smaller.

A quick way to check is to test fit a bushing from a Kato made model. If it fits easily then it's a frame for a Kato made model.  If it's a tight fit or won't fit then the frame is for the Classic version.

I was quite confused about this until John from Aztec set me straight.  The Aztec part number for the milled frame for a Kato made model is TM3001 and for the Classic model it is TM3016.

Because the outside of the Kato made and Classic frames seems identical, I wondered if the shells are interchangeable.  After swapping around several shells and frames I was able to confirm that yes, they are interchangeable.  So now on to the decoder installation.

This model normally comes with bright white LED's on a PC board very similar to the one used on the Kato made model.

On some of them there is a small component added to the solder side of the board.  This was added to suppress the flickering of the LED when the engine was running in the reverse direction in DC operation and will not be needed after the decoder is installed so it should be removed on both boards.

On the front LED board only there is a chance that the LED lead on the left side can short on the left side frame as shown in this photo.

The LED needs to be removed, a small tubing place on this lead of the LED, then the LED re-installed.  The Kato 77A LED board already has tubing on it's LED so I took some from those to use here.

I have also found some of these Atlas boards that have the circuit traces both sides (top and bottom) of the board. These have to have both sides cut to fully isolate that part of the board from the frame.

This photo shows the component side which normally does not have any circuit traces.

For the wire lengths I followed the Aztec instructions except that I added the blue wire and cut it to the same length as the yellow wire.

   Black & Red = 1-3/4",  White = 1-7/8",  Orange = 1"
   Yellow & Blue = 7/8",   Orange = 1",   Gray = 1-5/8"

This photo shows a summary of all the steps I did to get the decoder ready to install.  The wires on the Lenz decoder are soldered right at the edge of the decoder and I felt they might get broken during handling so the first thing I did was to gather them together in a heat shrink band.

This decoder had no heat shrink covering and it components were exposed.  This was the method I used to insulate it from the frame and from the rear LED board.

A scrap of .020 thick plastic was cut to fit on the frame, then the decoder was secured with some Kapton tape.  The Kapton tape is trimmed to fit around the bumps on the sides of the frame that hold the shell in position.

Here is a photo of the completed mechanism from the right side.  The gray decoder wire gets around the motor to the bottom brush using the slot milled in the right frame side.