Rebuilding Märklin 3000, DB 89 006 to digital with Märklin 60903 conversion set

Updated 25.03.2013

This small steam engine model is the number one regarding production numbers. The production started in Göppingen in 1953, then under the article number CM 800. In 1957 it changed to 3000.  In 2002 it was replaced by number 30000.  As far as I know, more than 3.000.000 models have been produced.  I have two of them, which I call 3000 A and 3000 B.  A is from the second half of the 70's and had an electro-mechanical reversing unit.  B is from the starter set 2915, and was produced in 1993.  It had a Delta decoder, fixed to address 78 by soldering pads.

For fun I have installed smoke deflectors on 3000 A and painted silver boiler rings on 3000 B.
I have painted the lower part of the locomotive body and parts of the chassis red.

This photo shows the parts removed from 3000 B (left half) and the new parts required (right half). I ended up using another decoder.  I had already replaced the Delta decoder with a 6080 decoder, to achieve more than the 15 decoder addresses available with the Delta decoder.
The screws for the new motor cover was not present when the picture was taken.
A new bulb socket insert is already inserted in the original bulb socket.
Two of those and two bulbs 610080 (22 Volts) comes with the conversion kit 60903.

Installation of the motor itself is very simple, except for the lower cover screw for the new motor.  See note. Remove the old motor and the reversing unit (or Delta unit), make sure that all mechanical functions, like the transmission, wheel axles and the rods, are good and that the locomotive is clean.

Note: The two long screws (2x12mm) for the new motor cover, that comes with the set, are too long to be used as the lower motor cover screw (yellow arrow).  The 12 mm long screw goes through the locomotive chassis, hits the final transmission gear from behind and blocks it.  I have used a screw from a normal drum commutator motor, left over from an earlier digital conversion of another locomotive, Märklin part no. 785140, 2x10 mm.  It is a bit short, but works OK if tightened carefully.  This screw is also used for the ground connection to the decoder, as I want to keep a clean visibility through the locomotive windows.  In the photo, the 12 mm screw sticks to the magnet for illustration.
I never throw away any leftovers, like screws, nuts or clips, as they might become handy some day.

Ground connection, 3000 A
To be on the safe side regarding ground connection, I installed a normal wheel on the rear left, instead of the wheel with a traction tire.  This will probably reduce the traction a little bit, but I think good electrical connection is more important.  I have also installed screws for the connecting rods on the centre wheels.  The threads were cut with a 2mm thread cutting tool.  This was of course done before any new parts were installed.
After some testing I will see if this conversion is required also on 3000 B.

Installed at the same place as the original reversing unit. I used a decoder from a 6090 conversion set. The decoder is installed in the holder 258820.
Decoder function:
3000 A: f0 = light with directional change, three lamps in both ends
3000 B: f0 = three front lamps, on in both directions - maybe rebuild later

Flicker free light in digital operation:
The 6090 decoder offers no regulated plus for the lights.  If the lamps are connected directly to the locomotive chassis, they will flicker according to the electrical pulses on the tracks.  One way to avoid this is to insulate the lamp from the locomotive chassis and to make a regulated plus by ourselves.
Solder the cathode (negative) side of a 2,7 Volt Zener diode to the cathode side of the rectifier diodes of the decoder (see orange arrow).  Our regulated plus is now on the anode end of the Zener diode (purple arrow).  The switchable negative current to the lamps are at the yellow (rear light) and gray (front light) arrows.  If only the front lamp is used, the yellow and gray can be connected together, so the front lamp is on in both driving directions.

Front and rear light:

Front light, 3000 A:
To insulate the front light from chassis ground, I removed the original lamp holder and glued on a plastic socket (475030) with a bottom contact tongue (475040).  The original bulb (600100) was connected via a 180 Ohm resistor, to reduce the too strong lamp intensity.

Front light, 3000 B:
A bulb socket insert, that comes with the 60903 conversion set (Märklin part no. 276770), is installed in the original lamp holder.  Just unscrew the original bulb, remove the C-clip, push the socket down in the lamp holder and install the C-clip. I use the 610080 bulb (22 Volts) that comes with the conversion set.

Rear light, 3000 A:
One rainy Sunday afternoon I wanted to install rear lights on my BR89 3000 A. In my spare part box I found three light guides from old NoHAB diesels. I drilled holes in the locomotive body in the center of the indicated lamps so the light guides fitted perfectly.
I glued on a two-pole SIL socket just behind the motor (careful not to make any short circuits) and fitted a 28 Volt T1 bulb.

The additional Märklin parts installed:
part no.
3000 Description
6090 1 1 Conversion set for dcm, only the decoder
60903 1 - Conversion set for sfcm, only the motor and the small parts
60923 - 1 mfx conversion set for sfcm, only the motor and the small parts
785140 1 1 Shorter screw for motor cover
258820 1 1 Holder for decoder
786790 1 1 Screw for decoder holder
475030 1 - Bulb socket
475040 1 - Contact tongue for the bulb socket
215220 3 - Light guides, from 3143, NSB Di3
471240 1 - LH wheel without traction tire
755030 2 - Bolt for connecting rod
280550 2 2 Coupler modification
232780 1 - Witte wind deflector, RH
232790 1 - Witte wind deflector, LH

Prototype information, DB BR 89:
Years in service 1934 - 1962
Road numbers 89 001 - 89 010
Axle configuration C
Service class Gt 33.15
Total length 9,600 mm
Max. speed 45 km/h
Max. power output 392 kW, 533 ps
Cylinder bore 420 mm
Piston stroke 550 mm
Wheel diameter 1,100 mm
Wheelbase 3,300 mm
001-003 35,300 kg
004-010 36,200 kg
Service weight 46,600 kg
Max axle load 15,000 kg
Boiler pressure 14 bar
Grating area 1.42 m2
001-003 89.2 m2
004-010 67.9 m2
001-003 No info
004-010 24.1 m2
Boiler tube length 2,800 mm
Coal capacity 2,600 kg
001-003 4.5 m3
004-010 4.8 m3
Produced by Henschel and Schwartzkopff