DCC Electrics problem

[Brew Man]

I guess it is possible that there is one with the same fault as many of the Hornby ones, given that there doesn't seem to be an obvious problem with the way your track is connected. Hopefully tests with your new multimeter will be revealing.

[Flashbang]

OK my bad!! The OP images looked like Electrofrog points hence my comments and they use IRJs too! I missed any mention of ST points being used throughout.

In this light its possible one of more droppers are crossed? It is also possible one of the points has lost its frog wire insulation separation under the point?

Only a logical disconnection and then reconnection one by one and testing after each reconnection of the points should reveal the issue!

Which is exactly what I suggested way back in previous posts!

[JB59]

In my very first reply to your post on 'Page 1' of this thread I made mention of FAQ4. This FAQ documents some guidance with regard how to use a Multimeter to measure resistance to identify a short circuit.

 

 

Thanks Chris

[JB59]

Multimeter arrived. Have tested every bit of track, including points, and on the 200M setting, all gave a return of 1.8. I guess that means there is no short ? I'm struggling with this now ! All droppers are connected to these blocks, one each for red and black wires.

A wire from each of them then connects to the bus via the six-way connector in my previous pic. I have 12 of the splice connectors on the bus so far, 1-9 worked perfect until the last three were connected. In theory with them all disconnected I should be able to connect 1-9 and get power to the track, but on connecting just number one the error appears ! Is it a voltage problem ? Is it an Elite problem ? As I said previously, without the droppers attached, with the twelve splicers connected I am getting 12V at the end of the bus.

[Chrissaf]

Not necessarily correct.

The resistance across the track should be infinite (open circuit). A reading of 1.8 on any meter scale is not indicating an open circuit.

If the meter is auto ranging, then potentially a reading of 1.8 could be 1.8 ohms even if on the 200M range.

Put another way, when the meter probes are not touching anything at all then note what the meter screen is displaying. This could be the number 1 or a row of dashes ---- or perhaps OL. If the track is 'open circuit' the meter should still show the same display when the probes are placed on the two rails, anything other than what I have just described is indicating a resistance is being measured.

Post a close up photo of the meter screen showing this 1.8 reading and I can give a better assessment of what it is indicating.

The track must be empty of ALL rolling stock when the reading is taken, also any electrical accessories connected to the track must also be disconnected, as well as any DCC Accessory Decoders. Your 1.8 reading could be indicating that you have electrical accessory connections still made to your track.

PS - You say you measure 12 volts at the end of the BUS. DCC is an alternating bi-polar squarewave. Thus you have to put the meter on the AC Voltage scale NOT DC Voltage. The reading should also be nearer 15 volts than 12 volts. The actual reading is only indicative as meters are calibrated to read Sinusodial waveforms not Squarewaves so could potentially read 12 volts but 14 - 15 volts is more typical. If you are reading 12 volts on your meter with the meter on the DC Volts range, then I have to ask the question regarding what other power supplies are you using on your layout and do any of these connect to your DCC Bus in error. When a meter is on the DC Volts scale, it should not read anything significant when connected to a DCC Track Voltage.

[96RAF]

I think one of your connectors is faulty.

Lets go right back to basics and take the Elite out of circuit and instead connect a 9v battery and buzzer or bulb across the bus wires. If there is a short the buzzer or bulb will flag the circuit. Even a single led and control resistor equivalent current will make the buzzer go off. Your multimeter may have a built in buzzer continuity selection which obviates the need for a separate battery and buzzer. The picture Chris has requested will confirm this.

Now you have to do the disconnect - reconnect thing again - tedious but necessary.

My terminal blocks have an led power indicator and they activated my buzzer, so it takes very little to ring out a short.

[Brew Man]

Just to add to Chriss's and Rob's advice, regarding the 1.8 you are seeing. Make sure when measuring you are not holding the probes by their conducting ends. If you are and the meter is on a high resistance range you will be measuring the resistance of your body instead of the resistance between the rails.

[JB59]

Here is a pic of the Multimeter set at 20M. Reading off the rails is 1, reading on all the rails is 1.

Interestingly, I have just connected splice connector 7 in my photo above and the whole system has gone live ! That is without splices 1-6 connected ! So my guess now is connect 1-6 one at a time and see if they work ? Alternatively, is there a way to test the two wires coming off each terminal block (with 12 droppers attached) to see if there is a problem with either the droppers or the connector block ?

[Chrissaf]

Note the switch position at the 5 o'clock position. The yellow one with a diode symbol and what looks like a wireless icon. The wireless icon is actually representing a continuity buzzer. If you select that switch position and touch the meter probes together you should hear a tone. This tone indicates that the probes are across a very low resistance.

Now what you can do, is leave the meter across your BUS with that switch position selected (assumes the meter came with adapters to turn the probes into 'crocodile clips') and then start connecting your track droppers and splices to the Bus, then when the connection that is generating the short is made, the tone should sound.

PS The "1" on the display is an open circuit (Infinity resistance) and should be what you should continue to see as you connect droppers (with the Bus not connected to anything else such as the controller etc).

[96RAF]

Check continuity twixt the suspect connector pole piece and the bus you think it is connected to, rather than the other end on the associated wire.

From what you say you have proven my theory that one of your connectors is duff or you have (despite your refutes all are correctly connected) got a cross connection.

[JB59]

Hi Chris, have finally got round to doing this. Every set of bus wires creates the buzzer sound whenever I connect them to the buswire. I have checked each piece of track and the wires are all back to the back rail and red to the front rail. Each red dropper is connected to a terminal block, and each black wire connected to a separate terminal block. That would seem like every set is creating a short ?

[Chrissaf]

You would seem to have made a fundamental error with your wiring methodology that probably needs a different set of eyes to spot (that is to say you keep missing the error that another would spot) the error. Since we can't look over your shoulder and see exactly what you are doing and you haven't provided any wiring schematics of what you are connecting to what. Then it is near impossible to offer you further targeted advice. Diagnosing short circuits is one of the hardest electrical issues for forum members to resolve remotely without being present and testing things for ourselves. It requires a logical and methodological approach.

Test the block terminals with the red and blue wire clamp levers individually (without any wires attached) for a short between the red and blue terminals. If these all pass OK, then at least these can probably be eliminated as a short circuit fault source.

[96RAF]

Here is another back to basics approach. Disconnect all wires from the track, then connect your buzzer across the rails. Switch all points. Do we have a short in the track system.

If not reconnect your bus one by one until you lock onto the crossed wire.

[Going Spare]

On the Peco website FAQ section concerning turnouts on DCC layouts, there is the following warning:-

"It is also important to note that Hornby de-isolating clips should not be used with Peco turnouts."

[Fishmanoz]

Not sure your back/black and front/red logic works? If you go around a loop from the nearer side of the layout to the further side, back and front rails swap. Then maybe I’m misinterpreting what you mean?

If I were you, after you’ve done the disconnections and start again as recommended (first checking terminal blocks and points), whichever rail you connect red to, I would put red labels on that rail near each dropper connection, following that rail right around the layout and into sidings etc until you have it labeled everywhere. Now start reconnecting droppers, testing for shorts as you go.

For all reading this thread - progressive testing of connections etc as you wire up a layout will likely save you from needing to start from if you don’t and you end up with a short. The problem is that there is nothing you can do to find a short once everything is joined together without taking it apart again until the short disappears or starting again, connection by connection. It is essential to monitor continuously as part of this.

PS. If in following around the layout labeling the red rail, you end up coming back to your start point and you are now labeling red on the opposite rail (keep going and the entirety of rails on the layout are red), then you have either made a mistake or you have a reverse loop (latter not indicated for the current layout).

[Brew Man]

From my perspective if you have a loop the near side rail will always be the near side rail no matter where on the outside of the loop you are standing. Or did you mean if you move to standing on the inside of the loop? I think I've confused myself now joy.