Dead NCE Powercab

[Scottl]

I was running trains this afternoon and took a few locomotives off the track to clean the pickup contacts.  I put them back on the track with everything powered and the system has been completely dead ever since.  I can't pinpoint precisely when the system went down but it was coincident with putting the locomotives back on the track.

I have a NCE Powercab and it has worked flawlessly for years until this point.  I was careful putting the locomotives onto the track to make sure they did not short. Now the unit appears to be completely non-operational.  The display screen is blank, the track power light won't light up, and trains won't work. 

I have removed all locomotives and carefully checked the track for shorts.  There are no shorts in the track indicated with a multimeter either. I've checked the power supply and it is functioning correctly.  I have also checked all the cable and plug contacts and they are all clean and nothing is bent out of place.  The cable between the panel board and the handheld is good- I checked all six wires for continuity.  I have unplugged everything and restarted it several times, and nothing brings it back to life. 

I'm hoping someone might have some suggestions or experience with a similar situation.  I could not find anything searching here and online.  I am hoping that I have not fried the system somehow.

[davefoxx]

I know nothing about NCE systems, but is there a circuit breaker or fuse that could have tripped?  Or, do you have the system plugged into a surge protector strip that has tripped?

DFF

[Scottl]

There is nothing accessible in terms of a breaker or fuse, and the power bar is operating fine.  I'm starting to get worried I fried the NCE unit...

[peteski]

Scott, I have a PowerCab and I have taken the throttle apart few times.  I just took it apart now again. There are no fuses inside.  The LED on the connector panel is powered by the track DC signal, so if the throttle is dead, the LED won't light up.

Sounds like you verified that the power supply and 6-conductor cable are ok.  Still, try using the 4-conductor cable in both connectors up front of the fascia panel. (just to try another cable and connector).  The throttle should still power up even with the 4-conductor cable (I just can't send the power to the track).

Also check the power supply voltage while the throttle is connected to the fascia panel.  There are couple pads behind the power connector marked "+" and "-".  Those should show the power supply voltage.  If when everything is still hooked up (try 6 and 4 conductor cables  and both front connectors) the power supply still shows 13.8V then the only possibility is that something died in the throttle unit itself.  I don't think there is much you can fix inside there.  If you are savvy with electronic circuits then the next things (inside the throttle) I would check is the voltage regulator (3-pin marked 7805, next to the cable connector) and possibly the microcontroller (chip in the socket).  When the throttle receives power and the microcontroller works, the display should light up, even if the track output transistors are blown.  But the backlight is controlled by the micorcontroller, so if it is dead, the backlight will not light up, even if the voltage regulator is working.

EDIT  I forgot - there is what looks like surge protector (2-lead component) on the fascia panel board. It is behind the track output connector. It is wired across the track voltage circuit. If you measure resistance across it, it should be open.

[Scottl]

Thanks for the detailed suggestions.  I'm handy with circuits so I will follow up on those after work.  Hoping it is something I can repair.

[Scottl]

Scott, I have a PowerCab and I have taken the throttle apart few times.  I just took it apart now again. There are no fuses inside.  The LED on the connector panel is powered by the track DC signal, so if the throttle is dead, the LED won't light up.

Confirmed, I took it apart and there are no fuses.  All components are intact, no evidence of frying something.

Sounds like you verified that the power supply and 6-conductor cable are ok.  Still, try using the 4-conductor cable in both connectors up front of the fascia panel. (just to try another cable and connector).  The throttle should still power up even with the 4-conductor cable (I just can't send the power to the track).

I somehow lost the 4-conductor cable...   I Checked for crossover between the wires in my 6-conductor cable and it is all fine.

Also check the power supply voltage while the throttle is connected to the fascia panel.  There are couple pads behind the power connector marked "+" and "-".  Those should show the power supply voltage.  If when everything is still hooked up (try 6 and 4 conductor cables  and both front connectors) the power supply still shows 13.8V then the only possibility is that something died in the throttle unit itself.

I have 14.0V from the wall wart, and when I plug the throttle up it goes into an unstable oscillation between about 2.3 and 6.5V  Very regular.

  I don't think there is much you can fix inside there.  If you are savvy with electronic circuits then the next things (inside the throttle) I would check is the voltage regulator (3-pin marked 7805, next to the cable connector)

The reg looks fine (it did not melt at least).  When powered it oscillates between about 1.3 and 3.8V in the regulated out pin.  This oscillation makes me wonder if one of the two power capacitors (470 and 10 uF) might be shot- both seem to be linked to reducing noise on track power traces on the PCB.  I don't have a means of testing the capacitors unless there is a trick?

 and possibly the microcontroller (chip in the socket).

The PIC chip looks fine, but there is not much I can do there.

  When the throttle receives power and the microcontroller works, the display should light up, even if the track output transistors are blown.  But the backlight is controlled by the micorcontroller, so if it is dead, the backlight will not light up, even if the voltage regulator is working. 

None of the transistors are visibly damaged.  There is no lighting or LCD activity to the display.

EDIT  I forgot - there is what looks like surge protector (2-lead component) on the fascia panel board. It is behind the track output connector. It is wired across the track voltage circuit. If you measure resistance across it, it should be open.

I wondered what that component was.  It was open circuit.

Not much to one of these throttles on the inside, which sadly means it might be shot.  One possibility for a fix is a replacement PIC chip if NCE sells those separately, and if that is the problem.  Otherwise, I might be out of luck.

Any other suggestions would be welcome.  I'll see what NCE suggests.

[peteski]

From your description it can either be the power pack itself (it fails when you put a load on it) or the voltage regulator in the throttle along with the ancillary components (the caps near it).  The power supply seems to me like the more likely candidate.

You can test the power supply by putting an external load on it. Hook it up to some 12V load, like an old locomotive headlight light bulb. Those usually consume about 60mA. If it lights up and the voltage is still stable 14V then the power supply is good.  Or if you have some resistors handy, just create a load (around 140 ohm for a 100mA load) and see if the supply remains stable under load.  But those resistors will get hot fairly quickly so be careful.

If the supply is good, you can attack the voltage regulator in the throttle. I would unsolder the caps and see how it behaves. Caps are more likely to go bad before the 7805 IC.

[Scottl]

Power supply checks out- I loaded it with two 60 mA 12V lamps.  I'll try the caps next.  I am pretty sure I have some 2A 7805 regs in the part box too.

[peteski]

Power supply checks out- I loaded it with two 60 mA 12V lamps.  I'll try the caps next.  I am pretty sure I have some 2A 7805 regs in the part box too.

To troubleshoot quicker, just remove the caps near the 7805, then test the throttle. As you mentioned, the caps just to stabilize the voltage and shouldn't be required for the 7805 to work properly.  Not that it really matters but a 7805 is a 1A regulator.

[Scottl]

OK, I'll see if I can get to it tonight.  Those two caps and the regulator are the only serviceable parts for me.

Hmm, 1A, eh?  Might not have a spare.  Digikey to the rescue if needed.

[peteski]

OK, I'll see if I can get to it tonight.  Those two caps and the regulator are the only serviceable parts for me.

Hmm, 1A, eh?  Might not have a spare.  Digikey to the rescue if needed.

Are you sure yours is 3A?  It must be some other flavor of the 78XX series as all of them are 1A regulators.   Maybe a 78T05 or somethign like that?  Still, it is a 3-terminal fixed-voltage regulator. The 3A version should work just as well as the 1A version. Kind of like driving a 600HP muscle car in the city - there is plenty of horsepower (or amperage) available - you just aren't using it all. 

[lajmdlr]

Have you called or emailed NCE? They are pretty good helping people that way.

[peteski]

Scott, I don't know why I forgot to mention this but the 14V voltage is also fed to the power transistors which generate the DCC track signal. Those are the transistors which touch the metal heat-sink plate on the battery compartment.  If some of those are shorted then they would be shorting out the voltage coming from the power supply.

[Scottl]

I decided in the end to send it to NCE.  It sat in a package waiting to mail until almost mid-October before I sent it.  Today, a package arrived from NCE with a repaired unit, no charge!  The display was gone, the thumbwheel worn, and the main board needed replacement.  They also put in the most recent firmware chip.  Needless to say, I am very impressed with NCE.  Kudos and my thanks!

[peteski]

Nice! I guess the only negative is that we will never know what component died.  I wonder if they simply just gave a brand new unit instead of fixing the old one?  Or is there some identifying mark on the case where you can tell it is your old unit?