MicroTrains GP35

The GP35 has a drop in decoder by Digitrax, the DZ123MO. Looks like there are 2 versions, one with big leds, the other with smt lets (surface mount).

If you have the big led version, apparently the fix is to install the board upside down. Correct the direction (easy on NCE, or set CV29 to 7, then change CV33 to 1 and CV34 to 2 to correct the headlight direction.  Also, you apparently need to break off a retaining post, where I don't know yet, but will get a picture.

The loco itself has been popular, and seems to run well out of the box.

That said, some do not run well, and are noisy. One rule of thumb is the current draw, they should pull abotu 50 ma at 6 volts, much over that, and there is some binding in the mechanism. Apparently the worm gear bushings are somewhat hard to get in place properly, may even shift when tightening the chassis. Some people have reported that loosening the screws 1/4 turn helps.

Make sure the trucks are free rolling. 

From Glen Chenier:

The worm bushings are hard to align, as you rotate each bushing you should feel a snap as the tab drops into the slot in the right side chassis casting. There are no corresponding slots in the left chassis casting, so when assembling keep the right chassis down to prevent the bushings from falling out. Sight along the worms and motor from the side, if the bushings are seated properly the worms shoul lie perfectly flat and straight. It tipped upwards a tab is not seated in it's slot.

The worm shaft bushings are NOT symmetrical, and their orientation is
critical, they have a definite front and rear. If installed backwards the loco will run slow and pull more current due to biding of the worm.

Look closely at a bushing, the tab is flush with the
bushing surface at one end with the indents in the bushing flat, but
is inset very slightly (abt 0.2mm) at the other end.

The inset ends must be positioned towards the worm. If not, the loco
will run very slowly unless the chassis screws are loosened and the
chassis halves separated slightly. When the bushings are oriented
properly the chassis can be screwed tight and the GP35 will run at
normal speed without causing binding of the bushings to the worm.

Also note there are thin flat shim washers at each end of the worm,
not shown on the assembly drawing that comes with the GP35. These tend to stick to the bushings, so if you have to turn one around move the shim washer back towards the worm.

If you ever have to take the trucks apart for cleaning, the 3 inside gears are not identical but are not named separately on the assembly drawing. They will fit the wrong way but will not run properly. The top gear that meshes with the worm is slightly larger than the other two and has 13 teeth. The lower two gears that mesh with the wheel axle gears are smaller and have 12 teeth. Make sure the wheelwipers are slightly touching both wheels at the same time without excessive pressure, and that the top of the wiper contacts the chassis.

 Glen's info:

A procedure warning of all the 'gotchas' can be found in the yahoo Z Scale enZyclopedia under Performance Zone / MTL GP35 Cleaning and Re-assembly  .

You should not have to completely disassemble a new GP35 to install the decoder, but note the motor springs have to be disconnected and how to prevent spring flyaway and making sure the wormshaft bushing tabs are properly seated in the chassis slots when re-assembling.  If these tabs do not seat properly the wormshafts will bind and the loco will run very slow.


DCC in MT gp-35 from Robert Ray

Subject: DCC'd my Geep... Easy!

The problem is all DCC format decoders are too wide. So, I just let it sit diagonal. All the decoders are too long except 3 models from Lenz.

The Gold Mini, LE0511, and LE0510 are all short enough to fit in the rear without obstructing the numberboards.

How to do it?

1: Remove contact springs from motor then gently lift the front of the light board up over it's retaining tab, slide forward, and remove the light board.

2: Bust all 5 tabs off with pliers, bending towards the outsides. They snap off easy, but bending towards the outsides, snaps them off clean and flush.

3: place a strip of electrical tape over the length of the top of the mechanism so metal filings don't fall inside. Remove tape after drilling.

4: use a #62 drill bit, and drill 2 holes, 1 on each side of the frame, 1/10" deep, then tap with an 00-90 tap from your MTL Coupler tools. Shake and blow filings out of hole.

5: Screw in a couple brass 00-90 screws that are used for mounting 905 couplers, and with your soldering iron on high, apply solder (tinning) to the screw heads for power pickup.

6: Put down a layer of Kapton tape (high dielectric) or electrical tape if that's all you can aquire, over the rear area where the decoder will go. Use a sharp exacto to cut exact fit on the top surface, not allowing any tape to go over the edges.

7: With the decoder on your left and the front of the locomotove on the right (the front is where that light board retainer post, the 5th post, was) cut to length then solder the black wire to the tinned brass screw head closest you. The red wire goes to the other side. The orange wire goes to the motor terminal closest you, and the gray wire to the opposite side.

8: Lights... The front LED can be re-used, but the rear cannot as it's too big. So, get some white SMT LED's. I got a strip of 25 white 0603 LED's that crank out 330 millicandles for $12 off ebay. Use a 1K smt resistor, which you can get from radio shack. I soldered the resistor to the Cathode end (usually marked with a green line, or has the most metal showing) then soldered the white wire to the resistor, and the blue wire to the Anode end of the SMT LED. That's the front light. The Yellow wire goes to the rear light, and is wired the same. You will have to splice the blue wire. Use shrink tube over your SMT resistor/LED assy.

Alternately, you can place the resistor in line with the blue wire, and just solder 2 blue wires on the output side of the resistor so you have blue wires for both front and rear LED's, then just solder up your wires directly to the LED's. The SMT resistor should support current enough several LED's.

9: Twist your decoder 45 degrees so it dangles diagonal off the wires, then your shell will fit in place, and the decoder will fit inside, even though the decoder is wider than the space inside.

I did my geep with a Lenz Gold Mini, in less than an hour. This morning I preped another Geep, with a Digitrax DZ-123, but it is too long. I need to get some more Lenz decoders.



DCC install MT GP35


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