Fitting decoder to a Bachmann split chassis Ivatt 2MT tank

[jp1]

Hi,

 

I've just fitted a TCS M1 to a split chassis Ivatt 2MT tank following the trains 4u fitting guide (why has this now disapeared from the list in the fitting guide forum?).

 

All seemed to go well.

 

I put a meter on the chassis to make sure there was no short between the two halves and I checked the front pony wheels were wired to the correct side. I also checked the connections on the two brass tabs were not shorting.

 

Now the problem, when I set up on decoder pro programming track it refuses to read the decoder. There is no problem with the SPROG or decoder pro as I used it for another normal DCC programming task.

 

One concern I have is that I cannot get any continuity between the top motor tag where the decoder orange wire is connected and any other part of the engine/chassis

 

Is there anything else I should check before I dismantle the engine again?

 

I would be greatful for any advice. Thanks.

 

John

[Butler Henderson]

If you do dismantle it again consider whether you can get a small piece of stripboard copper clad somewhere on the chassis like in the vincinty of the cab floor - if so instead of wiring the decoder directly to the motor etc , connect the motor and track pick ups to isolated strips on the copper clad, reassemble the chassis ensuring that the stripboard is isolated from the chassis (sticky pads) and test everything is okay. If so then connect the decoder to the stripboard.

[computrains]

Hi, I've fitted a sound decoder to a Bachmann J72 and perhaps my experiences may help.

 

On this loco, the pick up is through the axle bush to the split chassis. If there is too much grease in this high friction area, the decoder suffers and this can give mixed results. Difficult to programme and very difficult to run a low speeds.

 

Now, I wonder whether the effort to fit a decoder to a split chassis loco is worth the cost or effort.

[Combe Martin]

I've converted a split chassis Bachmann Ivatt to DCC. I used a Digitrax DN135D, and put it into the coal bunker to hide it properly under a real coal 'false top'. It's the smoothest running (at very slow speed) Bachmann loco that I have. It runs much better than all the more modern Bachmann steam locos that have the open frame motor, probably because the large worm gear is a flywheel too. It would seem that replacing the split chassis is a retrograde step because the newer mechanism is poorer.

[SRman]

I fitted TCS M1 decoders to both of my Ivatt 2-6-2Ts. I'm not sure if newer versions of the model have the extra pickups on the front pony wheels but both of mine did, so the copper or phosphor-bronze strips already attached to the chassis halves for the extra pickup wires served as good attachment points for the track wires (red and black) of the decoder. It was then a simple job to solder the orange and grey wires to the brushes, not forgetting to grind away the chassis contacts to those same brushes and fit heat-shrink tubing to the wires before soldering them to the brushes.

[34theletterbetweenB&D]

...One concern I have is that I cannot get any continuity between the top motor tag where the decoder orange wire is connected and any other part of the engine/chassis

 

Is there anything else I should check before I dismantle the engine again?...

 

No continuity between the top motor tag and any other part of the chassis is not a concern, it is exactly as matters should be for a successful conversion; both motor brush tags should be isolated from the chassis, the only path for current to the motor via the decoder.

 

One very simple test you might care to do if the decoder has DC running enabled, is try the loco on DC. If it doesn't run, then it could be nothing more than one broken connection in the circuit, which will equally well prevent programming.

 

... It would seem that replacing the split chassis is a retrograde step because the newer mechanism is poorer.

Get some sea time in!

 

While it is true that the split chassis mechs can with care be got to run very well on DCC - I have a B1 as one of the last split chassis types still running on my layout and it will do smooth dead slow movement perfectly - there are a heap of other problems with these types. Frequent need for axle journal cleaning to remove insulating muck already mentioned, the mechanical failure of the axle insulators, bowing out of wheelface inserts, and a relatively short life to wear out by loss of all the plating on wheel tyres, stub axles and journals all make me glad to see the back of this design!

 

Equally good performance can be had from the wiper pick up chassis, and I don't believe the three pole motor now used to be any hindrance. I have WDs with the original fit of a Buhler five pole motor, and the later Bachmann three pole motor, similarly the A1s with five pole Mashima and three pole Bachmann motors. All have Lenz silver or gold decoders, and perform extremely well down to a smooth dead slow crawl, no way of telling from on track performance which has which motor.

[Combe Martin]

Well I was refering to the motor mechanism (with it's flywheel) in the split chassis locos rather than the wheels, although the problems with these seem to have been solved in the more recent models. My Ivatt tank dosn't have those wheels.

 

But regarding the newer steam locos with the 3 pole open frame motor, every one of them runs jittery at the slowest speed (and I'm talking about walking pace, they are ok at faster speeds) and that includes locos fitted with Lenz decoders too, whereas all my Hornby locos (as fitted with their 5 pole motor) run more smoothly. I certainly can't get an S&D 7F to run smoothly slowly with a Lenz Standard or Bachmanns own 21 pin decoder, and that's with Bachmanns specially recommended Back EMF settings. I'm not the only one, I've talked to plenty of people at exhibitions who are running a DCC layout with steam locos, and they report similar jitteryness.

[Bibby Line]

A good friend has just chipped my loco (purchased some years ago) for me. It has a ZTC 255 decoder (despite the fact that i only use one function). The decoder is located in the cab and hidden by the Bachmann supplied driver !.

 

I am pleased to report that it runs well.

 

Eddie

[jp1]

Hi,

 

Thanks for all the advice and comments. I got round to having another go at it last weekend and I believe I had more than one problem.

 

I took it all apart and tested the motor alone on a DC supply just to prove it worked. Then I repeated the procedure with the directly connected motor in the chassis with the motion attached. This seemed to "unstick" something as there was a hesitation before the motor span up - probably the motion was binding.

 

When I re-assembled the chassis I found I had an intermittent short across one side and the motor. After some experimenting I believe that you need to be careful when replacing the three screws that hold the chassis together. If you start at the bunker end the chassis can "distort" and short out against the motor. Stating from the front screw and working back seemed to solve the problem and I took care not to overtighten. I added a small amount of insulating tape in the vicinity of the lower motor connection as well just to be on the safe side.

 

I also think the first time I re-assembled that one of the three small insulating washers between the chassis halves may have become displaced as I was puting the screws back in.

 

Also when re-assembling its important to get the motion lined up correctly. I had the piston rod arm snapped to the wrong side which meant it was binding on final assembly. This seemd to prevent decoder pro from registering the decoder, the motor always turns as the software is interogating the engine and stopping it move seemed to confuse the software.

 

So I believe I had an intermitent short, a sticking motion (at first), an incorrectly aligned motion and possibly a displaced insulating washer.

 

Once I sorted these problems the motor, chip and engine perform well on the rolling road, smooth and almost silent with very very good slow speed control.

 

John