Fitting Digitrax DH166D to an old Hornby diesel.

[OffTheRails]

Hello, this is my first post so if it is the wrong topic, or in wrong location or simply a dumb question I apologise.

 

I am fitting a Digitrax DH166 to an old Hornby Diesel, which has a ringfield motor....and the installation hasn't gone according to plan.

 

The motor was recently cleaned serviced and tested successfully.

 

The design of the motor connection and pick-up appears to be rear bogie is the left rail connection and front bogie is right rail connection. The connection from the right rail appears to be made to the rear half of the motor body, which has two connections, one to a terminal on the front of the motor (left), and the other to a diode and wheat grain bulb for the head lamp. The connections to the right side of the motor terminal come from the rear bogie which has two connections, one connected to the motor and the other to the wheat grain bulb.  Both motor connections appear to be connected to a capacitor. The connections were confirmed with a multi-meter.

 

My work to date has involved removing the wheat bulb and diode and replacing with the bulb with an LED, connected to the blue and white wire from the decoder. I have removed the capacitor between the motor terminals. Connections from the rear bogie have been connected together and then to the black wire on the decoder, the connections from the motor body have been connected together and onto the red wire on the decoder. The motor terminals have been connected to orange and grey wires on the decoder. Images below show the motor, the picture on the right shows the connection to the motor body.

 

Sadly when placed on the track and energised the loco did nothing, no smoke or pops from the decoder either. I ran the speed up to max and didn't even get a hum.... and the LED didn't work.

 

Does anyone have any suggestions on which way to go now?

 

Truly.....Off The Rails

 

 

[34theletterbetweenB&D]

First and most important: do you have program(me) track capability on your DCC system? If so, that's the facility to use to test any new decoder installation, or any change made to a DCC installation, to confirm a satisfactory installation by an address change, before giving the model track power.

 

Second, lighting is secondary. I wouldn't bother with it until the DCC decoder's motor control capability has been proven satisfactory on programme track.

 

These old Hornby motors are a PITA for DCC, because there is often a direct connection from one rail to one motor brush, independent of the wiring. (This is legacy practise from before DCC was ever thought of, live axle via the chassis block through the motor frame to the brush,  exactly as seen on all the old open frame motor locos from Triang/H-D/Wrenn.) Detach the wiring to the brushes, and put your multimeter on each brush in turn to check for any direct connection to either rail. If a connection is present it needs to be eliminated before proceeding to a decoder fit.

[OffTheRails]

Thanks for the reply. I will re-check for other connections and test comms on the program track.

 

Cheers

OTR.

[shiny]

I suspect that you may have already destroyed the decoder, but as 34theletterbetweenB&D has already pointed out  - do not put it back on the track until you have eliminated the short.

 

IIRC, those ringfield motors have a permanent connection between the wheels and the left-hand motor terminal, so pulling the wires off doesn't actually disconnect the track power from the motor. It isn't "DCC compatible" unless you do a bit of prep on the bogie first.

 

I can't tell for sure on the photographs, but if you look closely at the spade terminals in the motor, the left-hand one - where you have connected the orange decoder lead - is slightly longer. Usually there is a bit of plastic to hold it in place.

If you look even more closely behind the connector you will see a round 'pip' sticking up from the motor body and touching the back of the connector. The pip is made out of metal and is electrically connected to the motor body. Chances are that it will be causing a short circuit allowing track current to flow between the red and orange wires of your decoder. Pull off whatever wires you can from the motor bogie and check for continuity/resistance between the motor body and each of the motor terminals again. A low reading or beep from the meter is bad news. Repeat the check between wheels and motor terminals to be sure.

 

 

There are a couple of ways to prep the motor for DCC but you will need to take the motor bogie out of the loco in order to do it.

 

• There is a replacement ringfield screw that can be bought for DCC conversions, it is made out of nylon and is supposed to insulate the motor terminals from the wheels. I can't remember any more than that as I didn't use this method, but there are plenty of forum postings about it. This method however causes no damage to the motor bogie - the other methods do.
• You could take the plastic motor cover off and remove the metal pip using a dremmel etc - but take care not to lose the motor brushes and try not to fill the motor with metal swarf.
• My approach was to gently straighten the terminal strip and snip it short leaving just enough length to fit the spade connector on, then stick (I probably used superglue) a bit of plastic or card over the metal pip to cover it, duct tape should be OK instead. It isn't perfect because the bit of metal connector that is removed helps hold it in place - but it worked for me with a tiny drop of glue to stop things from moving around too much.

 

After you have made one (or more) of the changes above, check the terminals again before connecting the decoder. Making assumptions that everything is ok without double-checking is an expensive way of discovering that something isn't right.

 

Unfortunately this kind of short circuit is almost certain to have damaged your decoder; you would be very lucky indeed if it has survived the experience intact. If it does come back to life, be prepared for weird operating issues such as running away or refusing to go in one particular direction - you could always stick it into a dummy HST or something to work the lights if that is the case.

 

Having learnt my lesson the hard way I would never recommend hard wiring a decoder to a loco, and would suggest fitting a decoder socket into the loco so that you can remove decoder chips without the hassle of getting the soldering iron out every time you want to add or remove one. They only cost a couple of quid each from Hattons or EBay etc, but are well worth it in my opinion - especially if you want to upgrade/downgrade/repair/troubleshoot/sell the loco in the future. You can make your own decoder sockets easily enough for a few pence if cost is an issue.

 

Good luck.

 

Edited February 21, 2019 by shiny

[OffTheRails]

Thanks for the advice....key point being, I won't do this again! But I will check the left motor terminal, the spade connector is short has it fell apart during removal and I soldered on a connection.

 

Cheers

 

OTR

[OffTheRails]

Post Script.....

 

I found the offending connection, which I isolated by sheathing the motor terminal and spade bit with heat shrink insulation. Luckily for me I had cut one of the insulated joints that I had made in the track connection wire a little too short which resulted in a failed connection that saved the decoder!

 

I am going to buy lottery ticket whilst my luck is still good!