Fitting a Zimo decoder to a Heljan class 128 DMU
Tip description: Fitting a 21 pin sound decoder.
Cole4892 - Jan 11, 2018 wrote:
Just taken delivery of the latest Heljan offering, the first of the DMU series announced a couple of years ago.
The interesting news is that it is fitted with a 21 pin socket, so just a question of removing the blanking plate and plugging in your preferred 21 pin decoder. Space has been allowed in the chassis for an ESU 23mm diameter speaker.
The head-code boxes are lit and directional and there is a slide switch underneath for cab the cab lights.
Herewith the 'innards' - it took quite a while to take the body off after removing the retaining screws, the fit of the bulkheads is much on the tight side and there are a number of studs, (used to transfer power to the lights) that could have been a better fit, that got in the way - even more so when replacing the body.
The chassis is die-cast and the bogies are held on via 'circlips'. The loudspeaker will need to have a plug and socket in the line as the speaker housing is in the piece that is removed when the body fixing screws come out.
Cole4892, Jan 13, 2018
… I have now removed the body from the chassis and then the blanking plate from the PCB - and guess what, no indication on the PCB nor in the 'instructions' as to which terminals/pads are for the speaker wires. This and the fact that my comments above regarding the wires from the decoder to the loud-speaker, have been born out in as much as the two holes already through the chassis are too small even for a mini two wire plug and socket to pass through. Head scratching of the first order is needed before I proceed any further.
This is the Heljan PCB with the blanking plate removed. The Zimo instruction sheet shows the loudspeaker pins as No 2 & 3 from the top of the right hand line (adjacent to the left of CN5. CN1 & 7 are for the route indicator boxes and CN3 & 9 are for the cab lights and the two black leads (between CN2 & 3) go to the micro switch that controls the cab lights.
Perhaps CN5 is the connector for the loudspeaker, I have emailed Tower to see if they are any the wiser, I will report back when I have the solution.
Cole4892, Jan 14, 2018
The internal plan dimensions are 33.5mm long x 22.0mm wide it is all plastic and the columns are for fixing the ESU 23mm diameter speaker, although neither Heljan nor ESU supply the screws to achieve the fixing!
The double Zimo speaker that I have would just fit lengthways if I remove the two end walls and that is the preferred option (A) but it is how the wires are connected in such a way as to enable the whole of this unit to be detached in order that you can gain access to remove the body. The circular hole is for the 'shipping screw' to pass through to hold the base plate onto the chassis via a threaded hole. I will need to enlarge both holes to 6.5mm dia. to allow a two way mini connector to pass through, the widest dimension is 5.5mm, and just rest on the unit floor having poked the wire - long enough to allow initial separation of this unit from the chassis back through. There isn’t any space or recesses between the top of this unit and the underside of the chassis. I assume that the angled rectangular hole, there is a corresponding hole in the chassis, is for wire to pass through but in my mind does nothing to overcome the problem.
Cole4892, Jan 16, 2018
The lights ordered from Howes mentioned previously have arrived and they are the same size as those used on the O Gauge Class 31 that I tried. It is now down to using the ESU adaptor board ordered from SWD.
In the meantime I have cut out the speaker housing as supplied and in doing so the 'wall' at the top of the picture also came out as it formed part of the side walls. The provided pegs for the circular speaker screws were also removed to a level lower than that of the 'shelf' on the left hand side and the right hand side shelf was scraped down to the same level as the left hand. With the speaker in place, you are left with a convenient gap for the wires to pass under on their way through the rectangular hole and onto the adaptor board. The speaker will be held onto the shelves with strips of double sided tape or blue tack.
Next post should hopefully show the adaptor plate in position. Cole4892, Jan 18, 2018 I received the adaptor plate and mounted it on a suitable mound of Bluetac and worked from top to bottom (as necessary) with the plate angled across the bench, matching the angle that I offered the soldering iron and I was very pleased with the outcome. I soldered 150 lengths of the appropriate coloured wire so that I could then pair up with the red/black wires already fitted, away from the small pads on the plate. I have wired up the cab lights and interior lights as separate circuits and have by-passed the switch that is provided for the cab lights and used Swiss Mapping for this function.
All was well until I placed the model on the track and switched the power on - a short straight away. So off came the body and I set to with the meter, to discover very quickly that the pick-ups on the bogies were different at each end - motor bogie red nearest me, trailing bogie black nearest me - I had connected reds with reds and blacks with blacks elsewhere and all had been fine! It was a simple job to cut the trailing bogie wires and swap them over.
Body replaced and power switched on - all fine and some awesome sounds coming out from underneath!!!!!!!!!! Running number reprogrammed and Swiss Mapping done
Cole4892, Jan 19, 2018
Here as promised, a couple of shots of the adaptor board with the wires attached.
One with the Zimo MX644D in place.
The leaflet that came with the adaptor board was in German and there seems to be a slight conflict between the annotated diagram and the chart that follows the diagram.
