AC 6000 stuck in reverse at wide open throttle

Simple first have you tried to do a reset ?

NO, I cannot do a reset. The moment track power is applied the loco takes off in reverse at WOT.

It takes off with the Run/Prog switch in Prog?

What does it do with no TMCC/Legacy powered up?  What is its response in Conventional mode?

Unfortunately to me it sounds like the FETs on the RCMC are shorted.

only thing I can think it’s to try it conventionally with the run-PRG switch in Run and if it immediately takes off in reverse then I think you have your answer. With any luck one of our good techs will pop in and have another idea otherwise that’s a $120 board (it also may be possible to replace the FETs by a tech)

here’s the part breakdown to that locomotive HERE

What are the FETs on this board?   I do thank you for your help

They are going to look like this

unfortunately I don’t have a PN for the FETs (thought I had a close up so I had a PN but couldn’t find it) also I don’t know how difficult it may or may not be to solder.

@gunrunnerjohn may be able to help

The driver FET's are not super difficult to solder without damaging the board, but it's obviously possible to do some damage if you don't know what you're doing.  There are two types of FET's on the RCMC, the IRFR5305 P-Chan MOSFET and the IR024N N-Chan MOSFET, two each.

Thanks for the help, Zach and Gunrunner!  I do have another ac6000 so I may swap the board in that one and see what happens

I would put the "bad" board in the other one and see if the issue follows the board.  Also, I'd test the current draw of the motors in the failing locomotive "before" I put another good board into it!  Also, make sure there are no grounds on any of the RCMC wiring, especially the motor wiring.

I'm interested in how to test the amp draw of the motors. I've done it while on the track;however,I don't know technically how it's done. Do people remove the motor and run them on the bench to test amp draw? I can see where too high amp draw can take out the FETs. What should a normal reading be? Thanks.

Just unplug the motor drive connections from the RCMC board and you can then power the motors individually from a DC bench supply to test the current draw.  I just stick my Fluke bench meter in series with the power and then test at various voltages.  The standard Mabuchi 38x can motor used in most diesels shouldn't draw more than a 2-3 hundred milliamps running no load when attached to the power truck, usually less than 200ma when stand-alone.  If they're drawing significant power, the motor is almost surely dead or the power truck has binding in the gear train.

Thank you for the information.

I have taken the lid off of the two ac6000's giving me trouble. The one I am currently dealing with (runs full tilt in reverse) shows the two FETs closest to the edge having greenish bluish corrosion on their "legs". The other train(plays railsounds upon powering track and won't move) shows the two FETs away from the edge appear to have leaked something clear which has hardened in between the two and on top of the one on the left furthest from the edge. This is the FET which has actually leaked. I'm thinking each board shows visible trouble at the FETs. I do intend to test the motors-I want to learn how to do it any way. Thanks very much,again!  

Gunnrunner: the numbers  you gave for the FETs -are these good numbers by which to order these FETs?      IRFR5305 P-Chan MOSFET and the IR024N N-Chan MOSFET .    Thanks so much.

          Paul

@amos posted:

Thank you for the information.

I have taken the lid off of the two ac6000's giving me trouble. The one I am currently dealing with (runs full tilt in reverse) shows the two FETs closest to the edge having greenish bluish corrosion on their "legs". The other train(plays railsounds upon powering track and won't move) shows the two FETs away from the edge appear to have leaked something clear which has hardened in between the two and on top of the one on the left furthest from the edge. This is the FET which has actually leaked.

FETs don’t leak (at least not to my knowledge) if high current goes through them they might char and burn up though. The clear stuff you see is the flux from when the board was assembled they just simply were to lazy to clean it up.

I'm thinking each board shows visible trouble at the FETs. I do intend to test the motors-I want to learn how to do it any way. Thanks very much,again!  

Gunnrunner: the numbers  you gave for the FETs -are these good numbers by which to order these FETs?      IRFR5305 P-Chan MOSFET and the IR024N N-Chan MOSFET .    Thanks so much.

          Paul

Most likely you can take a continuity test to the RCMC that takes off and you should find two of the FETs shorted between the source and drain. As for the other one with the shell on does the cab light blink? Make sure there’s nothing binding the drivetrain, spin each flywheel by hand for one full wheel rotation to ensure there is no binding.

I have done a bit of "swapping" and of course when the WOT locos'  RCMC is installed into the other loco the "WOT in reverse when track is powered" condition follows said RCMC.  I tested the two motors in the original WOT Loco and they tested good.

The other loco is the AC 6000 that at times will just come to a halt while running and engine sounds come on and then loco won't move. Sometimes when applying track voltage the engine sounds come on and loco won't move. This particular loco with this problem has not failed since I re=installed the original RCMC. Hopefully all of the uplug and re-plug corrected a poor connection somewhere. I will leave this loco alone now and just deal with the WOT   in reverse when track power is applied loco.

I am indeed interested in attempting to solder in new FETs on the remaining loco. I have to find a source for the FETs or order a new RCMC board from Lionel.

This is my latest update on what I've done. Thanks to all who have responded and given help. It's much appreciated and not taken for granted. Thanks again.

@amos posted:

I am indeed interested in attempting to solder in new FETs on the remaining loco. I have to find a source for the FETs or order a new RCMC board from Lionel.

Looks like Mouser has both in stock.

https://www.mouser.com/c/semic...FR024N&instock=y

https://www.mouser.com/c/semic...fr5305&instock=y

Thank you,John. Very kind of you !  The first link has two different options and the second link has three options. Seems the specs on each option are the same;however, I do see the difference at theend of their part#.  Does it matter which options I order? Thanks,again.

As near as I could see, any of the choices appear to be suitable for the job.  I'm not entirely sure without studying the datasheets why there are different part numbers.

Thank you again,John. I will order the parts and see how it goes. I don't know how long parts,etc will take;however, I will post results as so  as i have them-good OR bad. No worries either way .I enjoy this facet of the hobby. If this doesn't work I'll just order a board from Lionel.

Thanks to all who have assisted and been involved. It's greatly appreciated.

Mornin', fella's. Well, my parts came in from Mouser during the week. Delivery was prompt.  I have soldered the new FETs onto the board and I've test run the loco for approx 20-25 min. It's run flawlessly thus far and I'm fully satisfied with these results.

My thanks go out the the those that helped me with this. There's just no way I could do this without the information that was provided to me by someof the members of this forum. Zhubl and Gunrunnerjohn- I thank you both for your help.  It's very much appreciated.

We love success stories.

Great to hear, I may have to pick some up myself just to have on my next part order 😉