TIU Melting Issues

Do a search and you can find the answer.  The interior nut probably came loose creating a resistance connection that generate excess heat at the terminal.  You can replace those connectors and tighten the nuts better.  Also test for DCS signal strength after the repair, to ensure no component damage.  G

Black Terminal Overheat on TIU Fixed Voltage In

Do a search for the above.

PhoebeSnow,

    I advise that you place the 10 Amp Scott type Resettable Breakers between all your transformers and the TIU Red Channels, when your repair your TIU.  I never run without them and have never had a problem.

PCRR/Dave

A breaker will not trip due to a bad connection. A bad connection causes heat, resistance increases with temperature so the problem just worsens. It is similar to putting the same current through smaller and smaller wire until it melts. That's why the breaker doesn't react.

John H is right.  Even a few amps through a bad connection can create a lot of heat.  There was another thread a month or so ago that recommended adding lock nuts, and gave the metric size to use.  The original TIUs, Rev G, had soldered connections, but them MTH switched.

Let me know if you need a new case for your TIU, I have a dead one that I use for parts, and I haven't needed the plastic case yet.

A someone posted in another thread, one solution is to add a lock nut.  He have the size as M4 .70, which I have used.

Thanks so much for the quick replies. They really helped me out. Hopefully sometime soon I can get the TIU apart to check it out. As for GunRunnerJohn, thanks so much for the generosity, and I’ll let you know how bad the damage is on my case. I might need to buy that one from you.

Thanks Again,

PhoebeSnow 

Maybe you can "melt" yours back into shape.

After posting the above, I opened up my 9-month old Rev L TIU.  None of the 16 nuts were loose enough to cause a poor electrical connection, but by my standard all were loose enough to warrant at least a 1/2 turn, which may have been compressing the star washer.  I do not make them so tight as to risk cracking the plastic.  A 7mm open end wrench is the fit.  I did go to Ace and buy 16 M4 .7 nuts and 16 #8 (SAE) internal point start washers, and will install them.

It appears that MTH had applied something like loctite on the threads, but it wasn't accomplishing anything.

John H,

   Never knew that!

RJR,

   Is the solder job on the older TIU's the reason we never saw this happening before?  If so MTH should have stayed with the safer engineering.

PCRR/Dave

Thanks, Dave. That's farm experience. I've had breakers melt, but still not trip. I have all my connections on the TIU  using banana plugs.  Are there still concerns with the nut?

John H posted:

Thanks, Dave. That's farm experience. I've had breakers melt, but still not trip. I have all my connections on the TIU  using banana plugs.  Are there still concerns with the nut?

Yes, the loose nut will affect any power on the terminal.

Dave, my 2 Rev Gs are soldered.  My Rev I and Rev L have spade connectors and nuts with external star washers.

I haven't checked out how the banana sockets are mounted (e.g., splined?) but it is it possible that torque on the socket would cause soldered joints to fail.????????

I know what I'm doing tomorrow. Thanks John. And more thanks for the help with your lighting module. Works great and the next one will be much easier.

Trouble withe replacing the case is the risk of damaging the guts during the transplant.  I'd be tempted to press out the terminals, and install new ones, using epoxy where the plastic won 't hold the terminal.  Won't be beautiful but it should work

Actually, the whole PCB and terminals pop right out of the case.  Replacing the case would be dirt simple.  When you split the case, everything comes out.

gunrunnerjohn posted:

Let me know if you need a new case for your TIU, I have a dead one that I use for parts, and I haven't needed the plastic case yet.

John would you have the screws to hold the tiu case together I lost the one I took apart and are somewhere in jy rug in the house. hope you can help me out ! Alan

After reading this thread, I have developed a very strong urge to take my TIU apart tomorrow and tighten all the connections you all are talking about here.

Also, as another related FYI, not all banana plugs are created equal, some make very poor connections and can even fall out of the jacks. May not melt your TIU, but could cause similar problems with overheating. I have tried about 3 or 4 different kinds before finding some at Digi-Key that seem to be working well so far. I was about ready to switch to a heavy soldered fork connection like the higher end audio cables sometimes use (or used to use anyway?). I did not realize the problem with banana plugs/jacks until getting back in the hobby and getting a DCS system a few years ago. Used banana jacks/plugs in audio for years and never really noticed them being loose and not fitting well? Not sure if this is due to recent problems with quality or a problem that has been around all along? Either way, I have become somewhat skeptical of them now.

Alan, I'm sure I could spare a screw out of my scrap TIU.

me to RTR I feel the same way as I'm building a new layout and don't need any added problems down the road after the layout is finished, would rather nip all these types of issue's from the beginning!

thanks for the good idea!

Alan

Now I know this may rub some folks the wrong way, but my feeling on banana plugs is that they are amazing for short term connections and relatively low current applications.  I have tons of banana plug and alligator clip jumpers I use to connect substitution boxes, volt meters and oscilloscopes while working on and testing various projects.  That said, when it comes time for a permanent hook up, or a high current connection, it is also time for a better connector.  That may be a soldered on U or O lug, or as simple as passing the wire through the hole in a post and screwing it tight.  In any case I don't trust the small contact patch of a banana plug on my transformers, or when running a few hundred watts of power to my speakers.  

BTW, lots of useful info here, and on the other recent post on this topic.  Thanks to everyone for sharing.  

JGL

John, I concur.  That's why I don't use them.  But we a small minority.  I don't beleive they have much contact area in the socket tube.  I use spade or ring clips.

I've used banana plugs from Radio Shack in the past. Some of these are loose in the TIU connectors right out of the package. I inserted  a small screwdriver in the plugs and gently bent the metal to make a fatter diameter plug. Do it for all 4 sides of the plug metal. So far to date, no failures.

Chris

LVHR

RTR 12.... do you have the model number of the Digi-Key plugs that seem to work?  Thanks in advance.

You can always check for heat if your TIU is accessible at the terminals.  It is also worthy to not if your running near a limit.  If your only drawing 2 or 3 amps, I imagine less of a chance of this occurring, versus a block pushing 8-10 amps.    G

An idea is to use one of the infrared temperature sensing guns after running at high amperage.

I wonder if MTH would deem adding lockwashers and locknuts to void the TIU's warranty?????

Gentlemen,

   I have been using the good Gold Banana plugs on all my TIU's old and new, along with all my Transformers, maybe that is why I never had a problem with anything like this ever happening.  I may have safe guarded against this problem long ago, and never knew it.

PCRR/Dave

I have a rev L TIU and so far all is fine but the banana plugs I was using does not fit the rev L TIU. 

I now use spade plugs. Did MTH change the size of the plug receptacles? They are smaller.

WDW (David) posted:

RTR 12.... do you have the model number of the Digi-Key plugs that seem to work?  Thanks in advance.

Thanks to Digi-Key's excellent record keeping, I do have the number, it's:  461-1214-ND They come in Red & Black pairs.

The problem with the others I tried were thin and flimsy metal used for the contact area on the plugs (some jacks are of poor quality as well). Bending the contact pieces (or whatever they are called) was only a temporary adjustment and they loosened up on their own after a period of time. One pair I tried was a high end (and $$$) audio set, same poor results. A while back I had a couple jacks under the layout that fell out of the MTH terminal strip and the trains wouldn't run, that is what prompted the search for a better plug.

FWIW, as I said in my earlier post, I am still not convinced these banana plugs are very good for train wiring? I tend to agree with the others that don't like to use them. I will probably end up going with a soldered fork connector at some pont in time (have not yet experimented with those). The way I am running my trains now, I seldom draw much over an amp or so per track, so I am probably ok for now (still going to check TIU internals today though). When I expand my layout, I will be taking a look at these connections again as some of the wiring will need to be re-done anyway and the TIU will probably need to be re-located as well.

RTR12: Thanks. Just ordered banana plugs for TIUs and power supplies from your DigiKey link.  Will make removing TIUs in particular much easier when needing to do anything with them.  They can be "built" at the bench adding Susan Deat's "filters" for signal, and Zener diode spike  suppressers to terminals before putting in place and attaching leads with the plugs.

David1,

   I use the good Gold Banana Plugs, although they go in a little tighter, they still fit perfectly in the Rev L TIU.  If you have been using the Cheaper Banana Plugs that do not compress well, you probably did have a problem with them fitting.

FYI, I thought the same as RTR12 about the Banana plugs, until I tried them years ago, when everything worked perfectly I kept using them and use them to this very day. I even put the stackable on the 990 Legacy Base, everything works great there also.  Retro-fitted the old ZW & KW Transformers with females for ease of operation and have never ever had a problem.

PCRR/Dave

 Did MTH change the size of the plug receptacles? They are smaller.

No, nothing has changed from earlier versions as regards banana plug spacing. When I swapped out my older TIUs for Rev. L's there were absolutely no issues reusing the same banana plugs.

Mine are dual banana plugs. The spacing between inputs on the plugs and on the TIU jacks are industry standard.

cnwdon posted:

RTR12: Thanks. Just ordered banana plugs for TIUs and power supplies from your DigiKey link.  Will make removing TIUs in particular much easier when needing to do anything with them.  They can be "built" at the bench adding Susan Deat's "filters" for signal, and Zener diode spike  suppressers to terminals before putting in place and attaching leads with the plugs.

You are welcome and good luck, I hope they work out well for you.

FWIW, I just finished checking my TIU connections and tightened the banana jack nuts on the inside. I am happy to report the connections were all tight and had lock washers factory installed. This is the first time the cover has been off my Rev L TIU that I purchased new when the Rev L's first came out. The Digi-Key banana plugs were still a very snug fit as well. Even had to pull pretty hard to get them out of the jacks. I am taking this as an indication of a good connection.

Checked all three of our TIUs with the following results:

Rev G (marked with silver marker on bottom after MTH repair Rev G  (No Fuses Inside): soldered connections/no loose nuts

Rev I 3 - very loose nuts requiring 2+full turns to tighten

Rev L - all required 1/4 - 1/2 turn to tighten.

Applied blue Loctite to threads at nuts.

None had signs of overheating. Surprised the Rev I 3 had not, they were very loose connections.

If the wire happens to have a good contact, sometimes it won't get that hot, even when it's loose.  I took one apart and found a similar thing, all of the nuts were very loose.  No sign of any melting, so I just tightened up everything with blue Loctite and put it back together.

Glad we bit the bullet and did the fix.   Hopefully they won't blow up when I put them back together and fire them up. 

Hi all,

I realize this is an old thread and long since resolved, by there is one aspect that was never covered that's worth noting.  If you use good banana plugs (here is my preferred choice in BANANAS) and leave the binding post tight you will never see this melting problem from a loose connection.  Why?  Because tightening the binding post on the outside has the same effect as tightening the nut on the inside of the case.  The binding post "nut" on the outside will screw down beyond the metal flange in the middle of the binding post assembly.  When assembled properly, the flange buts up tight against the case.  However, if the post is screwed down when assembled to the case, it's possible (likely) the post will become loose when you back off the binding post to install your wires.

There was a rash of failures some years ago (Rev H1) with cases melting when MTH transitioned from soldering wires to the binding posts over to eyelets and nuts.  The problem was caused when folks on the assembly line didn't back off the binding post nuts (the red or black plastic part) before tightening the internal nut on the binding post.  By the time the Rev. H2's came out the word seemed to have reached Thailand on how to assemble the posts properly, but they were still susceptible to working loose over time.  IIRC, the loctite started to show up on the Rev. I's.  Since then this has become a pretty rare problem, but it can still happen when someone new hits the assembly line in Thailand.

You can check for the problem by backing off the red or black binding post nuts and giving them a wiggle.  The plastic nut will be loose, but as long as the post is nice and tight to the case you're OK.  If the post moves AT ALL relative to the case, open up the TIU and snug up the internal nuts.  Just be sure to back off the plastic binding post nut before you tighten the internal nut.

Note he didn't state it was a fix, but a prevention method once tight inside.

Overtightening the thumbscrews beyond the needed torque to get the inner nut loose on thumbscrews next removal is the root cause.