Turned out to be a Faulty CC-M [Originally CC-M and motor-to-backplane connection questions]

Some diesel boards had VCO to know speed based off motor voltage to ramp up diesel sounds.  What are you doing with sounds?  ERR or staying with what you have?  G

George is exactly right, look at the motherboard and see if there's some circuitry other than just PCB traces, that's likely the VCO.  TAS used to have a chip on their diesel boards to do the diesel prime mover ramp-up function.

I see nothing other than a cap on the backplane.  The part no. is 691-PCB1-0B1 Rev B.  This is in a circa 2001 Atlas SD35.

It had:
DCDR, R2LC07, and RS3 board (sticker says RS25D25.

I installed:
Cruse Commander M, and a Lionel 691R2LCC08 (R2LC / RADIO RECEIVER (C08 CODE)).  RailSounds and RS Power board unchanged.

Where does that wire end up going?  I can only guess it's going to the Railsounds audio board, can you trace it out?

I'm guessing you didn't look that closely at the motherboard.

Yep, I see the cap you mentioned.

But wait!  What's all this on the other side of the board???  I see a chip labeled VC03, sounds like it would be the VCO to me.  The other chip is a 5V regulator.  U3 over in the upper left is an opto-isolator, doubtless to isolate the motor drive pulses from the VCO circuit.

Sure enough, you are correct.  I pulled the board out and that's what's on the other side.

OK, so here's why I was curious, and also why I'm tearing my hair out right now.

I have two of these Atlas SD35s.  Same generation.  Same electronics.  PRR cab nos. 2018 and 2025.  BOTH have been upgraded to an ERR CC-M and a Lionel R2LC08.  Both have the original RS boards.  The only other change I made was to reverse the motor polarity so one will run in reverse by default.  I guess I also swapped the lights front/rear.  No matter what I do, I can't get these to run at the same speed.

Things I've tried:
Setting speed steps to both 32 and 100.   (AUX1 + DIR + AUX1 + DIR + BOOST [100 steps] or BRAKE [32 steps])
Cruise on/off.
Motor size large/small.
I've also tried resetting the R2LC feature code. (PRGM switch, ENG + nn + SET + AUX1 + m)

I've also tried using the nudge feature (AUX2 x4, Boost/Brake) and I've tried resetting it (instructions say to just reprogram 32 or 100 speed steps to clear the nudge setting).

I've tested the drive train for binding, none found.  Trucks are identical, same gears.  Motors are all original. 

Using the nudge setting, I can get the two matched at a particular speed +/- a few a few thousandths every few feet of travel - close enough.  However, if I increase or decrease the speed after adjusting the nudge setting, they will separate by a large margin, with #2018 traveling quite a bit faster (usually).  I also notice after using the nudge, once I bring them to a stop, and then restart them, one of them will start smoothly while the other will lurch quite a bit.

Any ideas?

Sounds like you have some drive train friction issues in one of them.  Either that or perhaps a bad motor.  Since you have two identical units, you can swap one truck, then one motor, etc. and see if the issue moves to the other one.

GRJ,

So I took the (arguably) easier route and swapped the CC-Ms since I didn't notice this mismatch pre-upgrade.  The problem follows the CC-M.

Now, the question is - which one is bad?  Check this out, I noticed something a little different between the two boards...

One is green and one is black/brown!  Now I know manufactures often change PCB substrates and whatnot, but these are likely from different generations.  Both do have the same 2007 copyright year and have a sticker that says "CRM- 6.0" on top of the microcontroller.

Is there some magical CC-M reset dance I can do? (Other than the R2LC feature code programming which I've tried 20 times already)

Did you read the CCM instructions.  They have a nudge mode for Lash ups.  G

I honestly don't have a clue why they differ.  The board color doesn't phase me, that's not that uncommon.  I've changed the color of boards several times on some of my products.  I've also seen the CC-M in both shades, but I never noticed any difference between their performance.

@GGG posted:

Did you read the CCM instructions.  They have a nudge mode for Lash ups.  G

Yes.  As I stated previously, I used the nudge mode to get them matched at a particular speed.  However, once I did that and saved the setting, any change in speed thereafter (increase or decrease) results in the two engines bucking hard (if coupled) or running away from each other if uncoupled.  Additionally, the nudged engine (which I believe was the slower of the two) would jump pretty hard on starts from a dead stop.

So it turns out the CC-M was indeed faulty.  I ordered a new one from Sunset/ERR and got them to run together perfectly - no “nudging” required.

I bought the original more than 90 days ago so I guess I’m out $90.  Next time I’ll install and test as soon as I receive one. Lesson learned I guess!

@rplst8 posted:

So it turns out the CC-M was indeed faulty.  I ordered a new one from Sunset/ERR and got them to run together perfectly - no “nudging” required.

I bought the original more than 90 days ago so I guess I’m out $90.  Next time I’ll install and test as soon as I receive one. Lesson learned I guess!

Email Scott at 3rd rail and explain what happened,....what can it hurt?...worst he can say is no??.....Scott’s a real good guy to deal with.....he’ll be straight up with you.....I thought I saw another post somewhere where Scott said he’d exchange out of warranty boards for a small fee????........but let Scott confirm or deny that,....worth a shot anyways,....

Pat

@harmonyards posted:

Email Scott at 3rd rail and explain what happened,....what can it hurt?...worst he can say is no??.....Scott’s a real good guy to deal with.....he’ll be straight up with you.....I thought I saw another post somewhere where Scott said he’d exchange out of warranty boards for a small fee????........but let Scott confirm or deny that,....worth a shot anyways,....

Pat

Yeah worth a shot.

I contacted Scott at 3rd Rail and he had me ship the board back to re-flash it.  It arrived back today and it worked perfectly right out of the gate. My double headed SD35s are purring along together like a match made in heaven.