I think I just fried a DCC loco chip - diagnosis assistance needed

[imt]

It's the system that needs the motor connection to provide a current pulse that can be detected when programming the decoder on the programming track.

 

Decoders will happily accept writes with nothing connected, but you cannot read anything back, and the system may say there was an error.

 

This may have been the performance I observed.  Thanks for the information.

[HLT 0109]

I'm getting confused about this too.  I have an NCE PowerCab and a separate programming track with a different power supply to the main layout.  Are you saying that when the PowerCab is connected in the normal way to the Programming Track via its own PCP and switched to "Use Programming Track", there should then be no or little voltage detected in the rails?  Certainly that doesn't happen in my case - I still get the full 13.5 volts in the rails.  Or does it only happen if you get the Auto Switch device?

 

 

DT.

I am no expert and I have pro Cab via SB3a as well as Power Cab.  When I use the programming track, I switch off the power to the layout  and switch on the power to the programming track.  As I recall, my multimeter will then show little or no voltage to the programming track.  when I use the layout, I switch off the power to the programming track and switch on the the power to the layout.  I then run trains using bothe the Pro Cab and the Power Cab - but I cannot use the programming track.  I will check my statement tomorrow and report back.

 

However, is it not more relevant that the current should be minimal when using the programming track?  Power Cab can be set to display the current and, when used on my programming track, it shows 0.1amp.

 

Harold.

[Torper]

Well, that's not how it works for me.  My understanding, at least when using the PowerCab, is that the only function of a programming track is to enable the user to programme individual locos without any others being on the track to muddle things up.  In particular, according to the PowerCab manual, it "is needed to complete the necessary start up programming for most decoder-equipped locos".  This is achieved either by having a completely separate track, as I have, or by having an isolated section and a double throw switch on the layout itself.

 

I've checked again, and as I anticipated the voltage running through the rails of the Programming track when the PowerCab is set to programming track mode is exactly the same as the voltage on the main layout, ie 13.5 volts AC.  Until it is actually set to programme using the Programming track I can't see how the PowerCab could know know whether it's connected to the main layout or the programming track.  Amps shown on connecting to the Programming track are zero, on the main layout 0.4, but I put that down to the fact that there are a number of locos standing on the main layout.  Once the PowerCab is actually switched to programme using the programming track it no longer displays the track current so I don't know what that is though the track voltage remains at 13.5 volts even when I am in the process of changings CVs.

 

DT

Edited September 10, 2017 by Torper

[Pete the Elaner]

 

However, is it not more relevant that the current should be minimal when using the programming track?  Power Cab can be set to display the current and, when used on my programming track, it shows 0.1amp.

 

Yes, the current is more relevant.

Usually, current is V/R, so if it stays at 13.5v, then for a basic circuit, if the voltage is constant, the current should depend on the load.

DCC is a long way from a basic circuit. There should be a protection feature to limit the current to the programming track (or in the case of the PowerCab's default setup, a limit to the current through the layout when switched to programming track mode).

 

This is all getting a bit technical though..inevitable for DCC I suppose.

 

I did not realise the PowerCab's ammeter worked with a booster. I thought it could only work in its out-of-the-box configuration because the throttle which displays the current also supplies it.

The ammeter is a useful feature, sadly lacking from the PowerPro.

Edited September 10, 2017 by Pete the Elaner

[Nigelcliffe]

I'm getting confused about this too. I have an NCE PowerCab and a separate programming track with a different power supply to the main layout. Are you saying that when the PowerCab is connected in the normal way to the Programming Track via its own PCP and switched to "Use Programming Track", there should then be no or little voltage detected in the rails? Certainly that doesn't happen in my case - I still get the full 13.5 volts in the rails. Or does it only happen if you get the Auto Switch device?

The PowerCab operates the way NCE intended.   There is an unfortunate compromise to be struck in a device which has been price-engineered to not have separate programming outputs. 

 

 

BUT, for a "proper" programming track, as anticipated by those who designed the DCC specifications, that is not correct behaviour.

The intentions of the DCC design was that one could test an installation in a totally safe manner. If there is a fault in the installation, this programming test would not destroy the decoder.

 

Consider a faulty installation where the motor outputs are short-circuited back to the pickups.  This can happen in hard-wire installs (mistake by installer), and can also happen in factory plug-fitted locos (manufacturer has left a contact path from the track pickups to the motor terminals, which will run perfectly on DC with a blanking plug - I've seen this on mass-market RTR models).   

If in those circumstances, a DCC loco is put on a powered track (DCC or DC), the decoder now has its motor outputs shorted to the track power.  The decoder may fail (destroyed) immediately, or it may fail as soon as someone tries to run the loco.

In contrast, if placed on a proper programming track, there are no volts present, apart from tiny current limited pulses when programming happens.  Those current limits are important, they prevent the decoder from failing due to a wiring fault.  With the short present, the decoder won't give sensible values to "read", and the owner can take the loco back to the bench and investigate the problem, and then retest on the programming track.

 

 

 

 

- Nigel

[Torper]

Thanks Nigel - as usual, that has clarified matters.  Never having had any DCC system other than the PowerCab I hadn't known about separate programming outputs.  As a matter of interest, do many DCC systems currently available in the UK have these?

 

DT

[Izzy]

Would I be right in thinking, based on what Nigel has written, that due to the way it operates, the NCE programming track option isn't really the totally safe option that using a program track infers? That locos can have their decoders fried simply by being placed on it if there is short circuit in the wrong place?

 

The Gaugemaster/MRC Prodigy system has separate program outputs. Be careful though. In the early days of not knowing anything much about DCC, and being the idiot I am, I thought I could join both outputs together to the track, and only that which I chose would be 'Live'. Wrong! So within a short time of getting it........ it went back to be repaired, having blown the program track outputs. Oh dear. Credit to Gaugemaster for doing this under warranty without the slightest quibble.  It only took a few days, but thinking at the time it would be much longer that's how I ended up with a sprog II as an alternative. Probably the single best thing I could have done as regards DCC as it makes programming decoders so much easier to my mind.

 

Izzy

[RAF96]

Putting external DC directly onto a DCC equipped motor will definitely damage the decoder. It is a common mistake by people checking to see if the motor works applying DC direct to the motor brushes with a decoder still installed.

 

As stated there have been several instances of RTR models having wiring faults either bad wiring or solder tracking at the socket which has subsequently damaged a decoder. Also as stated in these cases a model will run on DC without any problems.

 

I am confused by this programming track with a separate power supply. NMRA is quite clear about the limited current, but less clear about it only being applied at the moment of programming, although many controlllers adopt this practice.

 

I sympathise with those who have killed their controller by cross connecting the various outputs terminals either accidentally or without reading the manual, as I did the same thing to my Elite when attempting to read all the output terminals for comparison on a four-channel oscilloscope. The low current circuits do not like having the full current outputs connected to them, in my case by way of crossed polarity rather than direct connection.

Rob

[Nigelcliffe]

Thanks Nigel - as usual, that has clarified matters.  Never having had any DCC system other than the PowerCab I hadn't known about separate programming outputs.  As a matter of interest, do many DCC systems currently available in the UK have these?

 

DT

 

Most have it done "properly" with separate programming outputs.  Those I know of which are correct include:  Prodigy-squared, Digitrax Zephyr and Chief ranges, Lenz 100 system (I expect other Lenz to be similar), ZTC, Hornby Elite, Uhlenbrock Daisy-2, Uhlenbrock Intellibox.  That list is far from complete,  I expect anything with a second separate programming output to be correctly implemented.  

 

The computer Sprog device also does it well, as its default behaviour is "track power off" and requires a software action in the computer interface to turn on track power to run a loco.

 

 

 

Would I be right in thinking, based on what Nigel has written, that due to the way it operates, the NCE programming track option isn't really the totally safe option that using a program track infers? That locos can have their decoders fried simply by being placed on it if there is short circuit in the wrong place?

 

The NCE isn't totally safe.  Its not terrible, but one needs to be aware of its limitations. 

If it isn't possible (easy) to turn off the track volts at a particular place in the instruction sequence to get to programming, then the decoder is at risk on the programming track *if* there is a fault in the decoder installation wiring.

 

The risk is fairly small, but it does exist in both hard-wired locos (installer mistake) and even in some RTR models (manufacturing mistakes). 

 

 

I think investigating the NCE programming auto-switch device is the best option for NCE PowerCab users. 

 

 

Putting external DC directly onto a DCC equipped motor will definitely damage the decoder. It is a common mistake by people checking to see if the motor works applying DC direct to the motor brushes with a decoder still installed.

 

As stated there have been several instances of RTR models having wiring faults either bad wiring or solder tracking at the socket which has subsequently damaged a decoder. Also as stated in these cases a model will run on DC without any problems.

 

I am confused by this programming track with a separate power supply. NMRA is quite clear about the limited current, but less clear about it only being applied at the moment of programming, although many controlllers adopt this practice.

 

 

 

I think the confusion comes from the PowerCab with its cost-compromise decision to have one output, rather than two, combined with a manual which isn't totally explicit on how things happen in this area.   The single output helped keep the price of the PowerCab down, but created the problem of when does the full track power get removed from the tracks to allow "safe the way the NMRA spec expected" programming to happen. 

 

 

 

 

- Nigel

[HLT 0109]

Confession Time!

 

As promised, I have just run some tests on my layout/programming track - and I have found things to be exactly as Torper has said.  I do apologise for muddying the waters.  With the power to my layout switched off and the power to my 2ft programming track switched on, my multimeter showed about 19v running in the programming track (0v to the layout).  I also found that i could run a loco on the programming track - something i hadn't even considered previously - and its speed did respond to the controller. Current appeared as 0.0 or 0.1amps.  Selecting "Use Programming Track" made no difference to the readings (although I could not run the loco).

 

With power to the programmin track switched off and that to the layout switched on, there was no reading on the programming track and about 19v on the layout.  Strangely, although my Power Cab will show current in "Use Programming Track" mode, it does not in operational mode.

 

In view of Nigel's comments, I agree with Izzy's concerns over the safety aspects of the NCE system and will bear the point in mind for the future.

 

Getting back to IMTs original post, it now seems less strange to me that his loco went shooting off when placed on his programming track.  DCC Concepts findings will no doubt resolve the issue.

 

Harold.

[RAF96]

From memory NMRA says 250mA max on the programming output, so many locos would respond at that level of current, although there is an associated time limit of I think 100mS in a current overload situation so the loco should not go too far.

Rob

Edited September 11, 2017 by RAFHAAA96

[Pete the Elaner]

Thanks Nigel - as usual, that has clarified matters.  Never having had any DCC system other than the PowerCab I hadn't known about separate programming outputs.  As a matter of interest, do many DCC systems currently available in the UK have these?

 

DT

I can't speak for all of them but there is a separate board avilable for the PowerCab which allows a programming track to be wired separately & auto-switched.

PowerPro has connections for both as standard.

[Torper]

 

I think investigating the NCE programming auto-switch device is the best option for NCE PowerCab users.

 

I don't think that actually achieves the desired effect, ie reducing the track voltage to minimal levels so as not to fry a decoder.  As I read the Auto_SW instructions on the NCE website, all it does is automatically change the power feed from the main layout to the programming track when "Use Programming Track" is selected on the PowerCab handset.  There's no suggestion that it does anything more than that.

 

I did read on an American site that in Programming mode the PowerCab delivers the same track voltage as it normally does to the main layout, but a reduced current.  I'm afraid I have no way of checking that.

 

DT

Edited September 11, 2017 by Torper

[Nigelcliffe]

I don't think that actually achieves the desired effect, ie reducing the track voltage to minimal levels so as not to fry a decoder.  As I read the Auto_SW instructions on the NCE website, all it does is automatically change the power feed from the main layout to the programming track when "Use Programming Track" is selected on the PowerCab handset.  There's no suggestion that it does anything more than that.

 

 

The auto-switch device responds to the PowerCab track signals, and the relay on the auto-switch then changes appropriately.

 

There is a detailed analysis of the AutoSwitch's actual behaviour (with oscilloscope traces) on the Yahoo group "NCE-DCC" by Mark Gurries. In the files area, called "NCE AutoSwitch Test Report".

 

The device removes risk to decoders of over-loading them when a short is present in the loco wiring.  The main issue seems to be to not put a loco on the programming track output until after the PowerCab has fully booted up (during initial bootup, there is a risk of inappropriate voltage and current being sent to the programming output of the Auto-Switch).

 

 

- Nigel

[Torper]

The auto-switch device responds to the PowerCab track signals, and the relay on the auto-switch then changes appropriately.

 

There is a detailed analysis of the AutoSwitch's actual behaviour (with oscilloscope traces) on the Yahoo group "NCE-DCC" by Mark Gurries. In the files area, called "NCE AutoSwitch Test Report".

 

The device removes risk to decoders of over-loading them when a short is present in the loco wiring.  The main issue seems to be to not put a loco on the programming track output until after the PowerCab has fully booted up (during initial bootup, there is a risk of inappropriate voltage and current being sent to the programming output of the Auto-Switch).

 

I'm afraid I'm not a member of Yahoo and so don't have access to the NCE group.

 

But I'm still confused.  I see that the autoswitch responds to the PowerCab track signals and the relay then changes, but that, as far as I understand, merely changes the track signal to go from the main layout to the Programming track.  There is no suggestion in the NCE instruction leaflet or on the NCE website that it reduces any electrical output.  If that's the case, it seems to offer little more than a DPDT switch except that it does it automatically.  As the voltage output from the PowerCab is the same whether in normal mode or Programming Track mode, how does the Autoswitch offer extra protection?  Or does Programming Track mode indeed output less current than normal mode and if it does that anyway, what's the advantage of the Autoswitch if, like me, you happen to have an entirely separate programming track with its own connections?

 

I'm sorry that these questions seem to be aimed at you, Nigel, as you are unfailingly helpful, but I'm just sort of thinking aloud!

 

DT

Edited September 11, 2017 by Torper

[imt]

If you have a separate programming track and an NCE PowerCab please don't go and buy an auto switch.  It does NOTHING other than sense the pressing of the "set program track" menu option to switch power to the main off and power to the program track on.  This is demonstrated by the attached official NCE diagram.  The diagram shows the auto switch being used to simply switch the main OFF - the programming track is permanently powered.

 

I can find nothing on the web that supports the idea that the programming track power should or must be off in what NMRA call Service Mode, or indeed of any particular voltage, however the NRMA states:

 

"3) Service Mode operations should be performed in an environment with limited energy to prevent damage to decoders during programming. For the purposes of this STANDARD, limited energy is defined as 250 mA, sustained for more than 100 ms."

 

I see no reason to believe that the NCE Power Cab does not issue programming commands in such a way, i.e. when the "set program track" option is selected then all the commands on the subsidiary menus are issued with lower energy and for short bursts as defined by NMRA.  HOWEVER what for sure does happen is that full volts are permanently available AND when you "escape" from "set program track" it is possible to drive the loco as normal, if it's loco number has been selected.

 

My problem was none of these things.  A previously well behaved chip was removed during some work on a chassis, and then replaced.  Placing that chassis on the separate programming track produced instantaneous run away, despite the loco number not being selected and the control wheel set at off.

 

 

Auto-SW Live Program Track (1).pdf

[RAF96]

Don't confuse voltage with current.

DCC voltage remains the same regardless of what mode you are in, it is the current which is limited in programming mode, thus I presume maybe the auto switch has a built in resistor circuit to so limit the current to match mode.

I don't have one so this is my best guess.

Rob

[Pete the Elaner]

Don't confuse voltage with current.

 

Judging from other comments elsewhere on this forum, this is a common mistake.

[Pete the Elaner]

If you have a separate programming track and an NCE PowerCab please don't go and buy an auto switch.  It does NOTHING other than sense the pressing of the "set program track" menu option to switch power to the main off and power to the program track on.  This is demonstrated by the attached official NCE diagram.  The diagram shows the auto switch being used to simply switch the main OFF - the programming track is permanently powered.

 

I can find nothing on the web that supports the idea that the programming track power should or must be off in what NMRA call Service Mode, or indeed of any particular voltage, however the NRMA states:

 

"3) Service Mode operations should be performed in an environment with limited energy to prevent damage to decoders during programming. For the purposes of this STANDARD, limited energy is defined as 250 mA, sustained for more than 100 ms."

 

I see no reason to believe that the NCE Power Cab does not issue programming commands in such a way, i.e. when the "set program track" option is selected then all the commands on the subsidiary menus are issued with lower energy and for short bursts as defined by NMRA.  HOWEVER what for sure does happen is that full volts are permanently available AND when you "escape" from "set program track" it is possible to drive the loco as normal, if it's loco number has been selected.

 

My problem was none of these things.  A previously well behaved chip was removed during some work on a chassis, and then replaced.  Placing that chassis on the separate programming track produced instantaneous run away, despite the loco number not being selected and the control wheel set at off.

That's interesting. Where did you find that?

Edit: I just found it NCE's help website. I find this very worrying.

 

When I googled NCE auto switch, I got the following, which is similar but has a very important difference.

https://www.dccconcepts.com/manual/nce-owners-manual-program-track-auto-switch/

This makes much more sense because it shows the board actually has connectors for the program track. Surely these should be for exactly that?

I would get your meter out before doing anything. When you select the program track, does it produce a voltage here, then turn it off again when you de-select the program track again? I suspect it will do.

Edited September 11, 2017 by Pete the Elaner

[NIK]

If you have a separate programming track and an NCE PowerCab please don't go and buy an auto switch.  It does NOTHING other than sense the pressing of the "set program track" menu option to switch power to the main off and power to the program track on.  This is demonstrated by the attached official NCE diagram.  The diagram shows the auto switch being used to simply switch the main OFF - the programming track is permanently powered.

 

I can find nothing on the web that supports the idea that the programming track power should or must be off in what NMRA call Service Mode, or indeed of any particular voltage, however the NRMA states:

 

"3) Service Mode operations should be performed in an environment with limited energy to prevent damage to decoders during programming. For the purposes of this STANDARD, limited energy is defined as 250 mA, sustained for more than 100 ms."

 

I see no reason to believe that the NCE Power Cab does not issue programming commands in such a way, i.e. when the "set program track" option is selected then all the commands on the subsidiary menus are issued with lower energy and for short bursts as defined by NMRA.  HOWEVER what for sure does happen is that full volts are permanently available AND when you "escape" from "set program track" it is possible to drive the loco as normal, if it's loco number has been selected.

 

My problem was none of these things.  A previously well behaved chip was removed during some work on a chassis, and then replaced.  Placing that chassis on the separate programming track produced instantaneous run away, despite the loco number not being selected and the control wheel set at off.

 

Hi,

 

I've just tested my NCE Power Cab (no autoswitch) with a power resistor (actually three in series) in parallel with the track.

 

In normal operating mode the NCE Power Cab meter showed 1.25 amps being drawn. Using a DMM that happens to give a good indication of the DCC voltage when set to AC (12.6V off load from a nominal 13.8V DC power supply) the voltage dropped to 9 volts when the resistor was in parallel.

 

Selecting the programming track mode the current meter continued to read 1.25 amps and the voltage on the meter stayed at 9V. I checked the current being drawn by measuring the voltage across one of the series power resistor - it was the corresponding volts for the indicated current.

 

As soon as programming track mode was selected the Power Cab displayed the message "short circuit detected".

 

The voltage on the power supply supplied with the Power Cab when the power resistor was in circuit was at 13.7 volts DC so did not appear to account for the voltage droop - it could be my wiring.

 

So it looks as though my Power Cab at least may have little programming track mode current limiting at 1.25 amps or maybe none at the hundreds of milliamps level.

 

Regards

 

Nick

[imt]

That's interesting. Where did you find that?

Edit: I just found it NCE's help website. I find this very worrying.

 

When I googled NCE auto switch, I got the following, which is similar but has a very important difference.

https://www.dccconcepts.com/manual/nce-owners-manual-program-track-auto-switch/

This makes much more sense because it shows the board actually has connectors for the program track. Surely these should be for exactly that?

I would get your meter out before doing anything. When you select the program track, does it produce a voltage here, then turn it off again when you de-select the program track again? I suspect it will do.

 

I am not sure what you find worrying?  It seemed clear to me for a long time that the auto switch did nothing in particular, OTHER than what it was described as doing.  Shutting off power to the main layout.  Now I don't have one and don't want one, but there were lots of suggestions that such a thing would somehow make using a separate programming track with an NCE PowerCab "safer" or somehow make it comply with standards that all (most?) other systems complied with. I don't think it does anything of the sort.

[imt]

Hi,

 

I've just tested my NCE Power Cab (no autoswitch) with a power resistor (actually three in series) in parallel with the track.

 

In normal operating mode the NCE Power Cab meter showed 1.25 amps being drawn. Using a DMM that happens to give a good indication of the DCC voltage when set to AC (12.6V off load from a nominal 13.8V DC power supply) the voltage dropped to 9 volts when the resistor was in parallel.

 

Selecting the programming track mode the current meter continued to read 1.25 amps and the voltage on the meter stayed at 9V. I checked the current being drawn by measuring the voltage across one of the series power resistor - it was the corresponding volts for the indicated current.

 

As soon as programming track mode was selected the Power Cab displayed the message "short circuit detected".

 

The voltage on the power supply supplied with the Power Cab when the power resistor was in circuit was at 13.7 volts DC so did not appear to account for the voltage droop - it could be my wiring.

 

So it looks as though my Power Cab at least may have little programming track mode current limiting at 1.25 amps or maybe none at the hundreds of milliamps level.

 

Regards

 

Nick

 

Not having an electronics background I don't understand what you did or what it proves or disproves. More explanation for an idiot please?

[Torper]

I've been reading the PowerCab manual again.  On page 46 it says: "The programming track does not supply enough power to run your locomotive.  You can only run trains on the main track....".  Near the end, under "Helpful Tips", I found the following: "Programming Track: The command station checks for a short circuit on the Programming Track before applying power.....This short detection is there to protect decoders from damage if they are miswired.  For this reason we always try a new decoder installation on the programming track first instead of putting it directly on the layout"

 

That all seems fine except that in Programme Track mode there are still 13.5 volts running through the rails which is of course enough in terms of voltage to run a locomotive.  So is the difference maybe in current - if it doesn't supply anough amperage, would that mean that locos couldn't run and (hopefully) decoders won't explode?

 

DT.

[imt]

Don't confuse voltage with current.

DCC voltage remains the same regardless of what mode you are in, it is the current which is limited in programming mode, thus I presume maybe the auto switch has a built in resistor circuit to so limit the current to match mode.

I don't have one so this is my best guess.

Rob

 

Sorry Rob I didn't think I had?  Lots of people keep telling me that there should be no voltage to the track in programming mode.  I thought that was what I said.  Also there is voltage to mine using a PowerCab and the NMRA doesn't say there shouldn't be - only that the instructions should be given with "limited energy" (their words not mine).

[Nigelcliffe]

I'm afraid I'm not a member of Yahoo and so don't have access to the NCE group.

 

But I'm still confused. .........

 

Yahoo is where Mark Gurries posted it.  I'm not going seek permission to copy his document to this forum.

 

   

 

(Not in response to anyone in particular).  Don't assume manufacturer's manuals are always accurate or complete.  They're often edited badly from earlier versions and may have mistakes or unclear statements in them. 

 

Mark Gurries testing of the NCE Autoswitch is thorough.  If wanting to know what's going on with programming from a PowerCab with and without the Autoswitch, then read that document first. 

 

 

 

- Nigel