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Does anyone know the purpose of the connection between the motor driver output from the ACDR/DCDR and the modular TMCC/RS backplane?  I’m upgrading an older loco with a DCDR to an ERR CC-M and I’m wondering if that connection is still needed.

The schematic below depicts the connection.  Follow the blue and green wires from the yellow wire nuts to the connector circled in red.


78B7B124-8DCC-47A4-B9B1-8D198F52F9C3

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Last edited by rplst8
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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.

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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?

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.

IMG_20210308_222006898_HDRIMG_20210308_222020648_HDR

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Last edited by rplst8
@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.

@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.

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