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Hornby R2204

BR 4-6-2 Merchant Navy Class 'Bibby Line', 35020

Review & DCC
Decoder installation -
Text & photos by Doug Teggin

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Prototype Info:

Built at the Eastleigh works in 1945, 'Bibby Line' was rebuilt in 1956 and withdrawn in the early months of 1965. It is unfortunate that this locomotive has the dubious record of being the only member of the class to be cut up by BR.

Class Introduced: 1956; Loco Weight: 97tons 18cwt; Driving Wheels: 6ft 2in.

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Length: 290mm; Running number: 35020 'Bibby Line';
Livery: BR green (early emblem); Period: Mid 1950s; Features: Sprung buffers;
Finish: Pristine; Motor: 5 pole skew wound loco drive; Purpose: Heavy express passenger;
Suitable rolling stock: Pullman cars, R4057, R4115, R4114, R4116, R4117, R4125, R4124.

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Metal buffer on the front of the loco along
with some optional accessories (ladders and pipes). The cab is not as
detailed as the A4 or the Q1, but it's ok. It's lack of detail won't
distract from the overall appeal of the loco.

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The tender is nicely detailed. Ladders,
sprung metal buffers and pipe work make it even more interesting. The
brake rods under the tender are supplied as optional accessories.

Decoder Installation

Follow the supplied instructions to
take the loco apart. One screw under the front bogy and a couple of clips
under the cab and you're done. You don't have to force
anything - if you do it right, it comes apart easily.

I installed a Arnold Digital 81201
into the Loco. As there are no extra functions required by
the locomotive a simple, but robust decoder is fine. The 81201 can
handle 1.5 amp. The Merchant Navy Class 'Bibby Line'
model draws 0.15 amp when rolling by itself; 0.35
amp when held stationary at the buffers, but with wheels freely sliding
on the track. The
locomotive (with tender) can pull 1.42 kg
(6 x 150g coaches + 4 x 130g coaches).

The installation was a little bit
tricky, not as easy as the previous two installations due to the lack of
NEM 652 (NMRA Medium) socket and more importantly: a lack of internal space for the
DCC decoder. Where installing a DCC decoder in a loco that has a NEM
socket may take about 10 minutes, this installation takes over an hour
because you have to do some trial fitting and adjustments.

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Note: The TV interference
suppression capacitor has to be removed for DCC use.

A capacitor is only needed for conventional operations to prevent radio interference.
With DCC operation a capacitor corrupts the data format and the error free data transfer is disturbed.
A snip with a small cutter does the job. I removed the capacitor and
exposed all the wires (below left).

Cut off the NEM Plug from the decoder if
it has one and
following the wiring diagram, attach it to the pickup wires and motor
terminals. The red decoder wire is attached to the wire from the right
wheels on the loco and the wire from the pin connector of the tender
(lower copper brushes on the tender hook of the loco). The black decoder
wire going to the left wheels on the loco and tender. The orange decoder
wire goes to the lower motor terminal; the grey decoder wire going to the
upper motor terminal.

The DCC chip sits attached to the inside of the boiler roof directly
above the gearbox in front of the motor. It is cramped in there so you
have to tape down the wires to prevent them jamming the chassis when it
goes back into the body. A few layers of double-sided tape keeps the decoder secure.
Tape everything
in place with black electrical tape and close up the body.

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Circuit component Electrical wiring Computer hardware Hardware programmer Electronic component

Note: This locomotive does not have
lights so the function wires are not used.

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DCC CV Settings
for the Merchant Navy Class
CV120Address (The loco
CV22Minimum Speed (V Min at
step 1)
CV34Acceleration delay
CV44Brake Delay (0-15)
CV5180Max speed (V High)
CV650Acceleration Curve (V
CV9216PWM frequency (69Hz)
CV292Decoder Configuration
CV490Decoder specific values
CV5020Decoder regulation

The rest of the CV's are left
untouched (factory default).

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One big issue with the latest Hornby models that use this system to
transfer electrical current from the tender to the locomotive via copper
brushes on the tender hook. The tender hook itself is conductive, then
there is a plastic ring insulating it from a plate above. The tender hook
feeds current from the right tender wheels and the plate feeds current
from the left tender wheels. Sometimes the brushes on the loco that are
meant to touch the plate, get jammed on the plastic insulating ring and
end up in contact with the tender pin (see upper left photo). This causes
a short-circuit and shutdown of the DCC control system. When attaching the
tender to the loco, make sure the brushes are in the right place before
turning on the power. Photo upper right: A: Left wheels brush from
loco are correctly touching the plate on tender; B: Plastic ring
where brush can catch causing a short-circuit; C: Right wheels
brush from loco touching the tender pin; D: The length of the
tender pin that is conductive.

A very attractive model. Beautifully made
with the good detail.
The locomotive runs very
smoothly. Under DCC control, it moves off on the first speed step, without
any jitter or hesitation. It will look good on a classic layout hauling a rake
of coaches or a collection of heavy goods vehicles.

- April 2005

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All text, photos & graphics ©2005
Doug Teggin - All rights reserved.

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