20-2645-1 F7ABA high current

Yes, you should run the front A unit alone and see if it acts up. If not, then add the second unit and see. Continue adding things, one at a time,  until it acts up.

When it acts up, remove the last thing you added and see if it runs OK. If it runs OK, then the problem is in the last thing added and then subtracted.

High current different then a voltage spike.  Yes you can run Lead on it's own.  But, I would take off shells and that way a basic inspection and then watch motors when running.  Either Center rail Red wire is shorting some where to chassis, or you have a motor issue that cause high DC current draw.  Are you running smoke off?  That eliminates a smoke heat element short.  Could be lead A or the slave, maybe a motor stalling. G

Thanks,  I will do some troubleshooting over the next couple of days

Took shell off and inspected for any obvious short. Nothing seen; in fact everything seemed to have a black sleeve where wires went through chassis. I went ahead and replaced battery with BCR. Engine with shell off operated normally for first few minutes then the current started to jump around between 0.8 and 2.0 amps. I stopped the engine and the current continued to jump. I noticed that there was some smoke coming from the stack even though the smoke was off. I turned smoke on and the fan came on and smoke blew out normally. I turned smoke off and the fan quit blowing but smoke continued to come out. Now the really strange thing is I shut down the engine with DCS but the smoke unit continued to smoke (no fan). I had to turn transformer power off to have it completely shut down.  Thoughts??  (FYI this is with the main engine only on track)  Again everything seems to operate correctly as far as speed control, lights, horn, bell, couplers.

You have the heating element shorting to chassis.  If you can unplug the the purple brown wires from smoke element with 2 pin plug, otherwise remove 4 pin connector from the PS-2 3V board.  The other potential is the Smoke element FET has shorted, and that provides a continues power to the element unregulated.  But since this starts out fine then gets bad with some run time that might indicate as the element heats up and expands some it might be touch smoke house case internally.  That allows the Positive voltage from the bridge rectifier (purple wire) to go through element and return to chassis AC ground because the brown wire side is touching housing.  G

Thanks George. I removed the 4 pin connector and the engine operated correctly for 30 minutes with no current surges. So we now know the problem is associated with the smoke unit. Not sure this eliminates the FET as a potential problem. I did check that heating element measures around 8 ohms and is not shorted to case (of course this is not heated up).

So do I just need to buy a new smoke unit? Or is this something where I can open up the smoke unit and try to reposition the heating element? If FET is shorted, is that repairable?

Ken

Pop the smoke unit open and see how close the resistors are to the sides on the unit and also if the little plastic insulation is inside. The insulation usually prevents the resistors from touching the side of the case. Also check for any splits in the wiring. Just some stuff to double check before sending the board for analysis.

I agree with George and Lou, eliminate the obvious wiring/smoke unit issues before you start suspecting the board.

I would do the visual inspection on bottom of board.  The large FET at front side of bottom board is the heat fet.  Hard to miss.  I imagine it would show a sign of damage, though the whole doesn't start messing up until a few minutes stumps me a little.  G

Thanks. I  hope to get back to this later this afternoon.

I checked the wires and all looked good on outside. I opened up the smoke unit and one of the resistors was bent some where one side looked like it would be really close to the case. I straightened it up gently and put everything back. I have run it for 30 minutes and everything is working and no current surge. The smoke turns off/on properly.  It appears to be fixed, so thanks everyone for the suggestions.

I will run it without the shell for another hour or so just to make sure, but feeling pretty confident

If the smoke resistor was shorted to the side of the bowl, that would most CERTAINLY cause high currents!   I suspect you have it fixed, and the price was $0.00.