Prodigy Advance 2 DCC unit Modification

Get rid of the SVdA fault caused by a short circuit.

Warning opening the unit and doing this modification will certainly invalidate any warranty.
But see the note below


Having used the Gaugemaster Prodigy Advance 2 for some while I was getting more and more fed up with the SVdA signal appearing every time a momentary short circuit appeared on the layout. These shorts are usually caused by forgetting to set a point on your route and running into the closed section of the point.
Once the short occurs the unit trips out the power to protect the system and brings up the SVdA display on the handset.
All well and good but you have to clear the short then either turn off the power or unplug the handset to get it to reset itself. More often than not once the short is cleared then your loco will tear off in the direction it was going and probable smack into something before you get chance to even reset the controller and wind down the speed. Even worse is that the stored Loco numbers available by the recall button get lost and you have to re-enter many of them.
What is needed is some way to prevent the current exceeding the limit that causes the dreaded SVdA warning to appear.
The answer is simply to fit a suitable lamp bulb in series with the power feed to the track so that in the event of a short circuit occurring the lamp will light up while limiting the current flow to a safe level that the main control unit can accept.
A suitable lamp is available in the form of a vehicle 12 volt Stop and Tail bulb with both of the filaments used in parallel. The way this works is that the resistance of a filament type lamp is very low when the lamp is cool so has little effect on the power supplied to the track but gets much higher as the bulb warms up. So what happens when a short occurs on the track is that the bulb lights up giving you an indication and the current flow is limited to a level that doesn't trip the controller.
(With the Stop and Tail lamp suggested the short circuit current is limited to 2 Amps) Simply remove the short circuit and everything will continue as it was.

Note:
After publishing this page some people have said that the SVDA still comes in even with the lamp in circuit. Experimenting with different bulbs has revealed that the stop and tail lamp can take the short circuit current very close the level where the SVDA fault kicks in. There seems to be slight variances in different manufactures bulbs where some will draw a little more current than others.
Before fitting the bulb in the unit if you opt for that method then test it by connecting it across the output of the master unit and see if it still gives the fault indication. If it does then just use the single 21 watt stop filament on its own and everything should be Ok.

Note. There is no need to actually open the unit up to use this lamp protection system.

If you are worried about the warranty it could simply be connected into one of the two track feed wires outside of the unit.
However, I wanted to put it in as a permanent feature in my unit as it gets used on several layouts and it is much neater.

So here is how I did it.



step 1

Step 1
Remove the case from the Master Base Unit. The screws are locate underneath the 4 feet which are held in place by tacky adhesive and can be removed or replaced easily.
Locate and remove the link wire shown in the picture. This link can be found at the rear of the unit near the output sockets.
Step 2

Step 2
Replace the link you have removed with a pair of wires about 6 inches (150mm) long.
These will be used to connect to the lamp bulb.
Step 3

Step 3
From a piece of Hardboard or suitable plastic cut a rectangle that will sit across the two heat sinks leaving the heatsink outer vanes unblocked.
Bore a hole in this rectangle so that the lamp bulb will almost but not quite fall through it.
Step 4

Step 4
Insert the lamp bulb through the drilled hole in the hardboard support and solder the two wires in place. One to the outside case and one across both contacts so that the two filaments are wired in parallel.
Then insulate the lower part of the bulb where you have soldered with plastic tape to ensure that when it is put in place there is no accidental contact with other components in the master unit.

See note above about different manufactures bulbs. You may need to use just one filament.
Step 5

Step 5
Place the bulb and its support so that it rests on the top of and is held supported by the two heat sinks. As mentioned above ensure that you do not block the air flow on the outer fins, Use a small dab of adhesive to secure the support in position on the heat sinks.
Step 6 Step 6
Replace the case with the 4 screws and press the rubber feet back into position.
Connect the unit up and test it by placing a short circuit on the tracks while the unit is turned on.
The lamp should light up quite brightly and any trains running will stop.
However the hand held should still show the loco information and not the SVdA fault code.

Remove the short circuit and everything should return to normal and you will have immediate control of the loco you were running.

Following the modification to my unit I first used it on my layout "Livsey Lane" at the Leyland exhibition in August 2012. I had 10 sound locomotives on the layout for the whole of each day of the exhibition. As well as running the locos the main unit was also feeding power to the station lamps, the arc welding unit via a timing circuit and the semaphore signal drive motors. The layout ran for the entire exhibition without any sign of the SVdA signal appearing on the handsets. On some occasions it was noticeable that the stop and tail lamp was dimly glowing when several locos were running at the same time but this had no effect on the operation of the layout and I can say that the modification is a resounding success.

As a result I will be carrying out the same modification to each of the units owned by the Heywood Model Railway Group in the near future.




John Essex Heywood Model Railway Group


This page updated 18th April 2014