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Model Railroading > Signaling (Part 16) – MP10 Buddy

Date: 09/09/23 01:48
Signaling (Part 16) – MP10 Buddy
Author: tmotor

This is Part 16 of a series on Signaling.  (Parts 1 thru 15 were posted earlier.)
All Turnouts need something to move the Points.  This can be as simple as an operator’s finger (assuming the Points are spring-loaded so they remain in place), but many times it is a “switch machine”.  These come in many shapes and sizes.  One of the most popular is the Tortoise.  A new contender is the MP10 by MTB (a company in the Czech Republic).
MP10 (Tortoise Replacement?)
The MP10 was just released this summer.  They are not common in the United States, yet. 
This is the 3rd generation of the MP switch machine product line.  (Previous generations are the MP1 and MP5.)  An existing Tortoise install can be swapped with an MP10, and it will function the same.  I like the smaller form factor, compared to the ubiquitous Tortoise.  The MP10 will be easier to conceal, and fit in most any install scenario.  It will be especially useful for a multi-level layout where depth under the deck(s) is at a premium.
Like the Tortoise, the MP10 has a pair of internal relays that operate when the motor throws the Points on the Turnout.  The Tortoise uses a “stall motor” design, so full power is still applied at the end of the cycle in either direction.  The MP10 has a more efficient design.  After it reaches the end of the cycle, an internal switch disconnects power to the motor.  This means it does NOT draw power after the Turnout is thrown.  Moreover, while the motor is in the process of throwing the Turnout, it only draws 150mA when operating.  Since the Demo Module is meant to be a Test Bed for different techniques and equipment, the MP10 will be run thru its paces.


Edited 1 time(s). Last edit at 09/09/23 09:51 by tmotor.

Date: 09/09/23 01:48
Re: Signaling (Part 16) – MP10 Buddy
Author: tmotor

Malfunction Junction
The MP10 has an internal 9-Pin connector that accepts a 9-Pin Plug-In Terminal.  The Plug-In Terminal has set screws, that drive anvils down to compress against the wire ends.  I wish the set screw terminals on the MP10 were of a design that makes me feel they will maintain a solid connection for many years, but unfortunately that is not the case.  They are a typical European design, where the set screw is turned Counter-Clockwise to tighten it onto the wire.  (In my mind, that just seems backwards.  Screws and bolts tighten in the clockwise direction.)  Another quirk is the face of the set screw does NOT raise or lower as the set screw is rotated.  The usual visual feedback is the raised set screw is loosened, and the lowered set screw is tightened.  This makes them even more of a head scratcher to figure-out.  (At first I thought the set screw had stripped threads, since rotating it didn’t raises or lower it.  Then I tried them all and they all had the same “feature”.)
I disassembled the set screw housing and could see there is an “anvil” that is driven downwards by the set screw (when rotated counter-clockwise) to compress it against the wire.  That is fine, but what about the rest of the connection path to the MP10?  There is a stamped piece of metal that forms a socket, which is needed to mate with the male pin in the MP10 Socket.  Then there is a tail extending from the socket that contacts the base of the set screw.  When the set screw is in the fully open position, the socket tail is mashed between the anvil and the set screw.  All 3 are making very positive contact.  The problem starts when the anvil begins its journey downward to press against the wire-end.  As the anvil moves downward, it no longer is contacting the socket tail.  The only contact the socket tail makes with the bolt shaft is spring tension, and not much of it.  If some corrosion or tarnish creates an insulation layer, then it will not maintain a reliable connection.  If the connection fails completely, at least it can be found and fixed.  However, if it becomes the dreaded “intermittent contact” issue, then it will only occur during operations, NOT when trying to replicate the issue during troubleshooting.  :-0 
If the contact between the tail and the set screw fails, it will be hard to troubleshoot.  The set screw will be tight, so it is assumed the connection is fine.  Everything up-stream and down-stream will be tested.  Only after exhausting every other possibility will the process of elimination point to the culprit, and the Plug-In Terminal is finally identified as the issue.  Been there, done that!  Got the T-shirt.
In the never-ending quest to eliminate these types of potential issues, and replace them with plug-n-play connectors, the “MP10 Buddy” PCB was born.  There are 9 connections needed for the MP10.  They are all low amp connections, so Ribbon Cable (26 AWG) can be used.  The 10-Pin connector on the Turnout Board is a piece of cake, which takes care of one end of the Ribbon Cable.  The other end of the Ribbon Cable connects to the MP10, which has set screw terminals. 

There were a few options explored to bypass or eliminate the set screws:
-Replace the MP10 9-Pin Plug-In Terminal with a connector having soldered attachments (vs. set screws).  Unfortunately, the 9-Pin connector is a proprietary design, with no soldering option available.

-Fan-out the end of the Ribbon Cable, strip-back each wire, and crimp ferrules on them.  This would work, but would be labor intensive.  This still doesn’t solve the concern that the Socket Tail is still only making contact with light spring tension.

-Design a PCB with a 10-Pin connector to connect to the Ribbon Cable.  Have a set of 9 Pins coming from the PCB that line-up with the openings in the Plug-In Terminal.
Buddy Boy
Another Buddy PCB would be a nice solution.  Ribbon Cable connectors are a very fast and reliable way to make multiple low-voltage (dis)connections.  Being able to retrofit a set screw terminal to interface with a 10-Pin connector will not only ensure reliable operation, but will look more professional.
The MP10 was disassembled.  Once open, it revealed a small PCB holds the 9-Pin internal socket.  Originally, I was going to cut-away the shroud surrounding the pins, and solder directly to them.  (The other option was to unsolder the whole 9-pin socket from the PCB, but there are dinky SMD components nearby that would be an issue.)  Though this would work, it would require this modification to all MP10s, including any replacements.  Moreover, it requires lots of time to remove the shroud without affecting the dinky SMD components on the MP10’s internal PCB.
Assuming the internal 9-Pin socket is to be left intact, let’s turn to the 9-Pin plug that mates with it from the exterior.  It makes a secure connection, and won’t fall out due to vibration (since it takes a lot of effort to separate them).  It would be better to modify the 9-Pin Plug-In Terminal since that leaves the MP10 unmodified.  A test with a soldering iron confirmed the anvil takes solder well.  If the Header Pins (from the MP10 Buddy) were sandwiched between the set screw and the Socket Tail, that provides very positive contact.  When the set screw is rotated clockwise, the anvil is drawn upwards, and compresses the Header Pin against the Socket Tail.  Some solder will seal the deal and result in a reliable connection.  

As you recall, the top of the set screws do NOT move up and down as they are loosened.  If someone rotates them, and doesn't see any "movement", they could assume nothing has changed.  When in fact, they have loosened the connection.  If they don't rotate the set screw to its original position, and walk away, that wimpy connection is a ticking time-bomb; and there's no way to spot it.  With the entire connection now soldered, that is no longer a concern.  Even if the set screws were completely loosened, and removed, the soldered connection is still solid.  :-D
The MP10 Buddy board will extend over an inch beyond the MP10.  This creates potential leverage as the Ribbon Cable is inserted or removed from the 10-Pin connector.  A 3D printed bracket will provide support, as well as the mount for the pivot for the rod that will move the Points.

Edited 14 time(s). Last edit at 09/09/23 10:05 by tmotor.

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