7mm Adding sound to Heljan Class 20s

Discussion in 'Area 51' started by richard carr, 28 February 2018.

  1. richard carr

    richard carr Western Thunderer

    I received my Heljan class 20 with centre headcode the other week.
    Class 20s were some of, if not he very last locos to run in BR Green before being painted blue. 20141 was the very last one and was finally painted blue in May 1980, so it is just possible for me to have a green one with full yellow ends running in my modelling time period of 1980 to 85.
    I have a blue one already that I bough on Ebay a few years back that someone had done a very nice job of weathering and installing sound, I also have a green one from the first Heljan batch of locos. The plan had been to paint that with full yellow ends and run those as a pair.

    The new loco has spurred me on to finally do something. So here is how I installed sound in both green locos.

    The first thing I did was run one the locos on DC to make sure everything worked OK. I tested the current draw with a meter and found that at high speed the locos were each drawing 1.5 amps and close to an amp at low speed. The plan was use a Zimo MX645R decoder from Coastal DCC. These have current rating of 1.2 amps so not really enough for retaining both motors, so I decided to remove one of the motors.

    Starting with what will be 20141,


    4 screws hold the body on 2 at the front and 2 in the middle, these came out easily and there is no difficulty accessing them.


    There is a centrally mounted PCB with for the very first time colour coded wiring in the normal DCC colours. This PCB is held in by 4 screws which are easily removed.



    Her's the Zimo decoder


    I now generally prefer Zimo decoders to ESU Loksound ones, as they are cheaper, they are easier to add a stay alive to and often have more functions. This one was £95 .
    This is an MX645R meaning it has the NEM 652 8 pin plug on it. It also has wires for the speaker in purple, a brown wire for F2 output and at the other end a blue wire and a grey one. The blue is for the positive of a stay alive capacitor and the grey the ground (negative) . I'm going to use a TCS KA2 but you could make your own and the decoder has the current control diode and resistor already built in. The KA2 has the current control diode and resistor but that is ok and it works just fine.. So to add a stay alive there is no need to solder wires to the decoder which is a really good thing. ESU should take note of that.


    I have now removed the front motor, all you need to do is loosen the screw next to the motor and just lift it out and then unscrew the motor wires from the PCB. Remember to tighten the screw back up.



    I then had a good look as to what space is available for speakers. I have these 2 differnt speakers available that I got from DC Kits (they sell the Leggoman biffo sounds but only on ESU decoders), they also sell the enormous speaker that went in the class 128 parcels DMU. That size speaker isn't going to fit here. after a bit of trial and error the longer thinner speaker is the easier to fit in the large slot in the middle of the chassis.

    Rob Pulham, Osgood, fenman and 2 others like this.
  2. delticfan

    delticfan Active Member

    Keep the info coming this is great. I bought two blue 20s to pair up and add sound so all ears here.
  3. richard carr

    richard carr Western Thunderer

    Here's the next one from the original disc head code batch of 20s that Heljan did.

    There isn't really much of a change between the 2 batches. The steps came as separate parts for the modeller to fit with first batch of loocs, these are now fitted on the second batch but that just makes them very easy to damage when you are adding sound !

    The electrical inards are quite different. In the latest batch the colour coding of the wires and the labelling on the PCB make it easy to identify which wire is which and you just need to wire them to your decoder. The first batch of locos are bit trickier as we shall see.



    Lots of red and black and purple and blue wires. There is some labelling on the PCB which helps a bit.


    First job again is to remove the front motor


    Here's a better picture of the decoder, having the wires for stay alive already attached really does make life a lot easier.


    To wire everything together my preferred method is to use a small piece of PCB soldering the decoder wires to one end and the loco wires to the other. If there are a lot of common wires (and there are here) you might need 2 strips for that. I'm using one in this photo (the blue wire from the decoder) but in the end I needed to use 2. The wires are relatively easy to identify, the difficult one is the loco common. On the centre headcode version the wire marked common on the heljan PCB is the common. On the original version here, I don't think it is and at the moment I have finished the second loco so I can't tell you for certain yet but I will finish it off when I get back this weekend. I'm in China as I write this at 4:15 in the morning.


    I wanted to keep the fan operational, so to make the connection easier I removed the connector from the Heljan PCB, here are I am soldering 2 green wires to the 2 pins, the green wire will then be soldered to my pcb and the fan will plug in as before.


    The speaker is going to fit in here but unfortunately it can fall right down to the bottom and stick out of the fuel tanks so the white plastic card is just there to lift the speaker up a little by about 15mm.


    Here's the speaker in place now


    This just gives you an idea as to how big these speakers are.


    Here's the speaker wired directly to the decoder as is the TCS KA3 stay alive, a bit of heat shrink covers the join in the wires. To get it to shrink just touch it with the soldering iron, it doesn't melt it just just shrinks.


    And here is the pcb I made all wired up including the fan connector.


    Everything has now been put back in, my pcb is stuck to the side of the chassis with blue tack.

    The tape just keeps the wires tidy.

    At this stage it is now ready for testing and then I find out that the lights don't work and probably because the common the heljan pcb isn't really the common. I will find out this weekend.
  4. richard carr

    richard carr Western Thunderer

    I finished thee 2 off at the weekend and decided to do the third one too. It already had a sound decoder fitted but as it was a Loksound XL V3.5 without a stay alive pairing it with one that had a Zimo decoder probably wouldn't work that well.

    So it turns out that the common on the original green 20 is in fact the negative and should therefore be connected to the front and rear lights.
    So this how the wires should be connected.

    Bonnent End

    Red and Purple wires are the common and should be connected to the blue decoder common.
    The black wire is the disc lights and should be connected to the white decoder wire
    The blue wire is the red tail lamps and should be connected to the yellow (rear light) decoder wire.

    Cab End

    Red and purple wires are the common and should be connected to the blue decoder common.
    The black wire is the disc lights and should be connected to the white (front light) decoder wire
    The blue wire is the red tail lamps and should be connected to the yellow decoder wire.

    With that done it works ok although sometimes the tail lamps come on at the same time as the disc lights but much fainter. So maybe there is something wrong with the Heljan board or my wiring them up the wrong way round to begin with has buggered something up.


    Here's the blue 20. I bought this on Ebay a good while ago, the front axle isn't driven so it suggest that it has had a split gear removed.

    This is what it's like in side.


    It has a Lok sound V3.5 Xl decoder right in the middle of the chassis and a speaker on either side. For some reason part of the chassis has been cut away.


    I'm going to use a Zimo MX644D with an MTC 21 pin connection decoder, so I need an adaptor board. Here I have started to solder the motor wires to the adaptor board. The board is an ESU 51967


    This is a different board an ESU 51968. The first board turned out to be rubbish and the lights just did not want to work with it.
    Unfortunately the instructions for this are all in German, and I don't speak german. Although there are solder pads for the lights you actually need to solder them to the wires the same with the other wires. But the ones tha don't have wires you can solder to the solder pads.


    The other board, it just did not want to work !


    The final board all wired up and ready to go in.
    I just retained one of the speakers and removed the front motor just as with the others.


    All fitted back inside, the tapes to hold it in place and a few bits onthe adaptor board to make sure no shorts can happen.
    TheSnapper likes this.
  5. Overseer

    Overseer Western Thunderer

    Has anybody tried replacing the hair dryer motors used by Heljan with Canon motors to reduce the current consumption? As well as the EN22 1833 motors, Canon make some larger motors (sometimes available cheaply) which look like they would fit with an adaptor ring.
  6. richard carr

    richard carr Western Thunderer

    Not to my knowledge, and removing the worm from the existing motors is not easy they are a very tight fit. The same goes if you needed to remove the fly wheel, I tried and failed.
  7. Steph Dale

    Steph Dale Western Thunderer

    I've got flywheels off (large vice under flywheel, parallel drift, 8oz hammer), but getting the worms off is tricky. The same motors are used in Atlas locos and I know @Yorkshire Dave has managed to get the worms off those. I've seen the aftermath (broken gear puller) and I know his success rate is very much less than 100%...

    He did it to fit Canon motors. The conclusion we reached is that the motors are fit for purpose, but the independent drive in each bogie is the most significant limitation in performance.