Strange behaviour Legacy PRR NS Heritage 6-28338

I'd obviously open it up and check all the wiring to see if anything's loose.  Assuming that you don't spot anything physical that looks bad, it's probably time to start swapping parts.

First stop, replace the R4LC, it's the cheapest part.  It's sending the commands to the DCDS motor driver.  If you have a similar vintage Legacy from the 2008-2010 timeframe, you can swap the R4LC between them, see if the problem moves with the board or stays in place.  Remember to reprogram the TMCC ID, for this model that's the "factory reset".

The other suspect is the DCDS since it seems that only drive is affected.  I haven't seen one that maintains the speed, normally they either stop or take off like a rocket.  However, if the wiring is good and the R4LC swap didn't do it, this would be my top suspect.

John makes good points.  Being a modular board engine, here is what I have seen many times with your engine.  The OD of the modular boards is about the same as the ID of the shell.  First I would run the engine with the body off and see if you get the same situation.  My bet is you will not.  When installing the body, place the frame on the bench/track and in the middle of the body, spread the body as you lower it down on the frame.  Do not invert the body and try to drop the frame down in.  If you do not do the body like I stated, you will tilt the tight fit boards a bit and end up with the situation you have.  Great engine but the headache mentioned goes with many of them.

Before I do any work on those SD-70 engines, I pull the boards and let them run for a period of time in my Lionel board tester.  Other than problem mentioned, they run great and are not bad to work on.

John, being a Legacy engine with the modular boards, after engine# set, he still needs to do engine#,AUX-1 then press number 2 on the keypad for a Legacy diesel.  I was happy when the RCMC boards started showing up as we were able to do away with the AUX-1 code.

Interesting observation on the boards being moved around putting it together, I'll look to hear how this gets resolved.

Marty, the manual omits the AUX1-2, I looked to recommend the reset.  I was surprised it wasn't needed, but maybe it's a manual error.  I always thought the modular boards needed the steam or diesel code as well.

John a manual error.  Modular steam is AUX-1-1 and diesel is AUX-1-2.  The R4 board needs to get an identity.  I was happy when they started Legacy with the one and two code.

I guess you just can't trust those manuals.

Fellows, thanks for your suggestions. I failed to mention that I have been doing my testing with the body removed and that I did try swapping the R4LC from another Legacy diesel prior to making this appeal for help. I too looked at the manuals for a reset code and found none. Having found no reset codes, I just reprogrammed the engine number and hit the "R" key afterwords. Good to know about the 1&2 codes. Later yesterday, while running the chassis on the tracks and just after loss of throttle response, the cab lights suddenly flashed and it shifted to a low speed crawl much like a car in limp home mode. This morning as usual, it will once again run normally, but will fail eventually. For many years I have repaired MTH, and most other makes including pre and postwar, I wasn't so fortunate to attend the Lionel school and lacking the requisite testers I'm at a loss.  Any further thoughts?

Eric Hofberg

Did you program the R4 with the 2 code?  Try pulling the plug off the smoke unit and see what you have.

Marty, I just finished another test. I programed the existing R4LC with the "2" code and ran the engine for 28 mins. with full throttle control, but suddenly the sound quit. I cut the power and pushed the "R" button to no effect and then I reseated the sound board which restored the sound, but once again the engine would not move. I next reprogramed the R4LC, but the engine still will not run. I strongly suspect that after sitting for awhile it will once again run normally for a limited amount of time. BTW: at no time during the testing phase did it draw more than .7amps. The smoke was turned off, but I have not pulled the plug yet. What to do now?

Eric Hofberg

Is this the replacement R4LC?  If two of them are flaky in this engine, I'd probably move on to other parts.

I'd suggest you get your heat gun out and first get the engine to room temperature so that it will presumably run for a spell again.  Then, while it's running, gently (with the emphasis on gently), warm up the DCDS motor driver electronics and see if that causes the failure.

John:

This is the existing/original R4LC. I had already reassembled the donor engine. I agree that it may well be heat related. I may also pull the DCDS board and examine it for faulty solder joints.

Eric Hofberg

Since it runs for a spell before croaking, I lean to the heat issue.

On that engine you may see this when it comes to sound dropping out.  Follow the three wires from the volume pot to where they join the two wires from the speaker.   The 5 wires go into a Lenoco plug that plugs into the motherboard.  The receiver on the motherboard has been a problem.  If reseating the wires tight does not put you in business,  pull the motherboard and freshen up the 5 solder points on the board where the 5 pin connector plugs in.   You should get lucky.

the continuity for the 5 wires is as follows to the Railsounds audio board.  Pins 18 and 20 are speaker wires and the volume pot wires are 12-14-16.

I always start with my meter set to continuity and check the afore mentioned connections on the Railsounds audio board to the 5 pins on the bottom of the motherboard.

John, on the heat I am with you.  The Legacy motherboard has a 5V reg built on to the board.  I have seen those fail.   The fact that he still had a running engine when the sound quit points me to what I mentioned in my post.   

Chug, pull and reseat the Railsounds power board and see what you have.  The power board is the same part as a TMCC engine.  Try another power board and by now you should be fine tuned.  The sound related items mentioned are very common.  I buy Railsounds power boards several at a time.  Good item to keep handy as they are the same for TMCC and Legacy.

Fellows: I ran the engine on test rollers for 1 hour including 15 min. of heating with a high output hairdryer while running and no failure; I then immediately put the engine on my layout and I have been running it for 50 min. with no failure. I have reversed it and powered it down but no failure yet. I fully expect it to fail again and if I wanted to guarantee that I only need install the body, we all know how that works! Marty, I'll check the connections that you described. I'll keep you posted.

Eric Hofberg

Is your sound restored?

Marty,

The sound was restored immediately after I reseated the sound board. I apologize for not clarifying that part. The engine has been running on the layout for an hour and 35min. with no problems and this is in addition to the hour running on my test rollers. I have reseated the boards numerous times to no lasting effect, but it is currently running for no discernable reason. Maybe it needed the heat treatment! I will test again tomorrow, but I'm still inclined to to a look at the bottom of the motherboard before calling this fixed as I haven't fixed anything.

Eric Hofberg 

Happiness is a solid bug, too bad you can't be happy with that one.

I think looking at the underside of the MB may be useful, it sure sounded like a heat issue with a loose connection or heat sensitive component.

I have several Lionel SD-70 diesels.  They run great but all have needed some love to make them the way they are.   I have worked on many.  

I have several Lionel SD-70 diesels.  They run great but all have needed some love to make them the way they are.   I have worked on many.