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Got an interesting repair in.  An A-B-A that has two powered A-units, each with a K-Line cruise board.  Of course, you have figured out the story, the trailing A has fried it's cruise board!  OOPS, there are no replacements for those.

The logical replacement is an ERR Cruise Commander M, but the speed curves will be totally different, so that's probably going to be a significant issue.  The K-Line cruise and ERR cruise do not play well together.  So, I figure to replace both the working and non-working K-Line cruise boards.  Each unit will get a Cruise Commander M board.

Now comes the fly in the ointment...

The K-Line cruise boards just use serial data, but the CC-M wants serial data, the two PWM direction outputs, and the +5V DC from the R2LC!  That's three extra pins! That could get ugly!  I examined the K-Line cruise 1--pin tether, and to my amazement there are four ground wires out of the ten pins!  They have separate grounds for the coupler, lights, smoke, and the standard frame ground!  I just found my three wires!

Next up is the issue of driving two motor control boards from the R2LC PWM outputs, it doesn't have the drive to get it done.  Each motor control board has a set of opto-couplers to receive the PWM data, paralleling them causes all sorts of issues.  The serial data is also marginal, especially after it travels through a few tether connections to the trailing unit.

I've actually run across this before, but this time I decided that I should consider a way to do multiple powered units without having totally separate electronics.  I suspect this isn't the last time I'll see this same configuration.

Time to fire up the Circuit Board Design tools.

This is a board that will allow me to boost the serial data for the long trip to the rear, and also provides two buffered outputs for the PWM drive from the R2LC.  The buffer has sufficient drive to power three or four opto-couplers, two won't be a challenge.  This board will feed both the lead A unit CC-M and the trailing A unit CC-M with buffered PSM inputs.  The independent 5V power supply will also prevent us from overloading the R2LC 5V power output since it has very limited capability.

This board (when it comes back from OSHPark) will provide the buffering to tie these units together for proper operation.

TMCC Motor Driver Buffer 1.1 Schematic

TMCC Motor Driver Buffer 1.1 3D N1

TMCC Motor Driver Buffer 1.1 3D N2


Images (3)
  • TMCC Motor Driver Buffer 1.1 3D N1
  • TMCC Motor Driver Buffer 1.1 3D N2
  • TMCC Motor Driver Buffer 1.1 Schematic
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I've found that I can't do that, I have the example sitting on my workbench!  The direction control was "iffy", and about half the time the trailing A unit would suddenly go full throttle.  When I put a 'scope on the serial data, it's amplitude was less than 3V, that's getting down where the CC-M starts missing commands.

Since I'm delivering this to a customer, I like to make sure it's 100% bulletproof before I ship it.

Its a good idea. I was surprised mine worked. My backup plan would have been to just add a second radio board but using a single one makes for seamless running every bit as smooth if not smoother than two Legacy engines lashed up.

Likely not a drop in for every engine though. Mine was not cruise and came with a 6 pin tether so that had to be replaced with a ten pin.


I'm relatively illiterate when it comes to electrical circuits, but what you've done here seems pretty amazing. Because of my illiteracy, if I had this problem I would consider just taking the motors out of the trailing A unit and converting it to a dummy. For my use, at least, a single dual can-motored engine would suffice for my  pulling needs. I think so, anyway, given that I have single dual-motored engines pulling loads like six aluminum passenger cars and decently long freight consists without problems. On the other hand, if I had this situation and really liked the A-A set,  I'd probably send to GRJ for a complete makeover.

Out of curiousity, I have a K-Line A-B-A set with the two A units powered, but the engines don't have cruise control. Just to confirm, it is just the presence of the K-Line cruise that creates the problems, and adding ERR CCMs to a pair of K-Line A-A engines without cruise would be a straight-forward installation of the CCMs, wouldn't it?

In the case of this engine, when I put two CC-M modules in parallel, the trailing unit was not happy.  After looking at the pictures on the 'scope, I could see the signals were marginal.  I have no idea if it's just this particular set or a general issue, but since I've experienced a host of issues with the serial data stream that buffering it solved, I'm just added the boost for the PWM signals.

FWIW, I also use the PWM boost on my Smart Motherboard project, I found that the single DCDR (or CC-M) loaded down the signals enough that they couldn't be recognized by the on-board logic.

The issue with the serial data stream and CC-M problems are the stuff of legends, that's been talked about for years.  Even with the most recent CC-M, more than one person has encountered serial data issues.

Whenever you add things in a non-standard configuration, you have to think about the possible issues you may be introducing.

Breez, in your case one option would be to install a Cruise Commander in each engine. Your engine has two DCDRs not Cruise motor drivers driven by a single Radio Board. The DCDRs don't require serial data only direction (PWM). It becomes problematic when you have to use serial data to drive multiple loads which is the case if you put in Cruise Ms.

Johns circuit allows use of less expensive Cruise Ms rather than the more expensive Cruise Commanders.


It would work, however the beauty of a single "command" unit is no MU configuration and no getting out of sync with each other.  One of the constant issues with TMCC/Legacy MU configurations is a power interruption makes them forget they're in an MU and the revert their direction to "forward".

Yes, you can wire them to run backwards for "forward", but that makes them an oddball.

That being said, it would be possible to just remove the tether and do that.  However, I always wanted to do one of these this way, and now I'll have my little board to make it happen.

For many years I have been building multiple powered diesel units with a single Cruise Commander. With some modifications, it can handle four can motors just fine.

Since the drive transistors have super low turn on resistance, the limiting factor is the current rating of the bridge rectifier. I put a heat sink on the rectifier with heat transfer epoxy and mount a computer fan blowing directly on the heat sink. Works great.

I have at least four loco sets with four motors and one loco set with six motors.

Some months ago, I put a CCM into a K-line A-B-A with six motors. The motors are wired in series/parallel - each unit has the motors wired in series and the units themselves are wired in parallel. A small computer fan nestled between the drive transistor heat sink keeps the rectifier cool enough. The CCM has a different bridge rectifier that does not lend itself to mounting a heat sink as easily as the full Cruise Commander does.

The funny thing about this K-Line six motor A-B-A set is that it had a tether with only four wires. Two wires ran the additional four motors and one ran the rear headlight and one ran the rear coupler. That meant all the power/ground pickup was in the forward A unit. I rewired the tether so that the B unit also provided power and ground and phooey on the rear headlight and electro coupler.

This loco will pull a passenger train, so not a lot of uncoupling will be going on.

Last edited by RoyBoy

I've had less stellar results than Roy with running four motors.  I have several sets where it worked pretty well, but then a couple of others the cruise behavior was almost nonexistent.

I have to disagree about the drive FET's.  While in a perfect world they'd not dissipate much power, I've replaced FET's due to stalled motors on a number of Cruise Commanders and Cruise Commander M boards.  I've yet to have to replace the bridge rectifier on any of them.  I can't comment about exactly what in the design makes the FET's vulnerable to overload, they certainly seem to be the weak link in the chain.

I did one of those K line sets years ago, but converted to DCS.  It was interesting how K line drove the extra cruise board.  I have also done several MTH ABA set up years ago running both powered units off one CC at owners request.  It worked fine on several sets I did, and I do believe others have done it.  G

I am on to plan B. Rather than using 3 Cruise Ms I will try a Cruise M in the original powered A and a Cruise Commander in the other A unit also powering the B unit. Not ideal with two radio boards but hoping to get them running close with the nudge feature.

Intial testing with the single Cruise M powering all three units (6 motors) showed intermittent current peaks over 5 amps. Way to close to max especially given they were running light. The engines have little run time so also hoping some break in miles will reduce current demand.


Nothing set in stone. I will check the current draw on the CC with 4 motors and see if I am comfortable with it. I did find a piece of grit in one of the trailing A trucks that was locking the drive and likely contributing to the higher than expected current draw. Doing some cosmetic work now. I'll report back when the units are running again.


I've had less stellar results than Roy with running four motors.  I have several sets where it worked pretty well, but then a couple of others the cruise behavior was almost nonexistent.

I have to disagree about the drive FET's.  While in a perfect world they'd not dissipate much power, I've replaced FET's due to stalled motors on a number of Cruise Commanders and Cruise Commander M boards.  I've yet to have to replace the bridge rectifier on any of them.  I can't comment about exactly what in the design makes the FET's vulnerable to overload, they certainly seem to be the weak link in the chain.

IF you overload a MOSFET driver, it has such low on resistance, it is gonna burn...

That being stated, the Cruise Commander will handle 4 motors. If within the operating currents of the MOSFETs and running 4 motors with a consist, the Bridge Rectifier is the one to reach the highest temperatures.  Over the long term the Bridge will "leak" from running hot and then the diodes in the bridge won't block reverse current flow well.  While the bridge may survive, the MOSFTs will fail in this case. which probably explains why you see the MOSFETs fail.

Roy is correct, that the Bridge needs to stay cool, and thus the MOSFET drivers will not degrade and fail over time.


Last edited by SantaFeFan

Interesting information once again Jon, I kinda' wondered why the bridge dropping significant voltage (and thus dissipating significant power) didn't have an problem.  That being the case, wouldn't it have been prudent to put a heatsink on the bridge?

For the full Cruise Commander you could use thermal epoxy to stick a heatsink onto the bridge between the FET's and perhaps increase the reliability of the CC that way...

I love it when a new pearl of wisdom drops into the forum, thanks!

Last edited by gunrunnerjohn

I have not run four motors on anything with cruise but have an MTH Veranda converted to TMCC with a TAS SAW board. I removed the original heat-sink and mounted the TAS board on a finned copper sink like the one in my photo but cut in half length wise. We loaded it down with about forty cars and ran it about an hour with the body shell off and nothing got hot enough that you could not touch and hold your finger on. Tried it with the motors all wired Parallel and again with them wired two pairs each parallel and the pairs wired in series. It ran a bit hotter with all the motors parallel but not so much you could not keep your finger on the bridge or the triacs.  I also have a pair of Lionel PA-1s where I made finned copper sinks for the DCDR driving four 545 motors. Again wired parallel / series. Triacs and bridge run cool enough to hold a finger on them after pulling a load of 12 70' cars for 20-30 minutes. I ended up keeping the motors wired parallel / series on both, since both locos were plenty fast and could pull more cars than we were likely to hook to them.                                  j


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Last edited by JohnActon

Just a thought from an EE wannabe…

How hard would it be to build an “amplifier” for the drive MOSFETs?  Like, connect the motor driver outputs to a beefier driver board.  The motors in the main unit would still be directly connected to the CC-M, but then the first slave unit would have this amplifier. The inputs would be wired in parallel with master unit motors and outputs to additional motors in the first slave and any additional ones.  Then a pot to trim the gain.


Another project... I have the following... all with Can Motors from 2001.   Occasionally, I run them as MUs / Lash-Ups.   While not in the same league as my Visionline GG1... I really,  like them a lot.

K-LINE K2780-4935 Brunswick GG1

K-Line K2780-4892RS Brunswick GG1

K-LINE K2780-4907 Tuscan GG1

On a fast and furious learning curve... hope I'm up to the task.


Made two important discoveries with my 6 motor K-Line E-9s. First off, in the process of removing the truck sideframes for repainting, I had to separate the trucks from the motor. Not a big deal but it enabled seeing into the gearbox. All 6 were nearly dry. Before reassembling them I filled the gearboxes with grease. What I noticed after test running them that grease can run out the motor shaft bushing at the bottom of the truck. I suspect a lot of K-Line diesel trucks are made this way so check the bottom of the trucks and if you can see a shaft next to the mounting screw, grease can get out. I will cover that hole up somehow, not sure how yet, Flextape????

Also its been a while that I upgraded an engine that had capacitors across the motor leads. K-Line does this to smooth out the power. I had forgotten that Jon recommends removing these capacitors when installing a Cruise board.

When I first test ran all three engines connected to a single Cruise M the combination was drawing over 5 amps. Some of that was for lights and fan motors but mostly going to drive motors.

Now with all engines lubricated and capacitors removed the three engines together are drawing about 1.5 amps. Its actually fluctuates some between, 1.2 and 1.6 amps but still way low for six motors.

I am leaning now instead of using one Cruise M and one Cruise Commander I may go simply with one Cruise Commander. I should have plenty of headroom and won't have create a lashup with multiple RxLCs.

Moral here is yank those capacitors if you haven't already.


Dennis, are you talking about upgrading these with TMCC & Railsounds?  These are fairly easy units to upgrade.  According to the description, they are "upgradeable".

John,  Yes... They have sound and I believe it's RS-4, at least that's what I have in my notes.  RS-5 would be nice (and probably the speakers upgraded as well).  I run them with Legacy and the CAB2 remote.  Now that I have dependable switches (thank you Tortoise) I think it's time enroll in electronics school.

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