BLOWEN FUSE ON TIU

Pretty easy Sonny.  6 screws (Philip) on the bottom are removed to take the cover off.  You will see the 4 yellow mini fuses.  One for each channel.  G

If you are ready for a little adventure, turn the TIU face down and remove all the screws in the back of the unit.  Once open you will find the fuses close to the output jacks.

The fuses are the automotive type with two spades for connection.  Look for the blackened one.  Any automotive store will have the replacement size.

If it's a fuse, this is the part that you are looking for. If it's burned out you'll notice. I keep a handful around just in case. I've blown a couple, no big deal. You may bring the burned out one to a radioshack and they'll sell you a replacement. 

Thanks everybody I took the tiu by the horns, opened it and my tiu must be the first they made.  That's right no fuses.  I looked and looked nothing. Guess I'm just going too wait for the toath ferry for now.  Only I have store ones.  Thanks all. at lest I have 3 good ones.  Sonnyh

If it's the very first model with no fuses, take a look at the bottom of the board.  If you can see the outline of a burned trace, MTH refuses to attempt to repair those.  We have one at the club with the same issue, and we just use it as a 3-channel TIU.

Sonny,

When you turned the TIU upside down, was there a sticker in the middle of it? If not then you have a Rev G, the earliest version. As others have mentioned, MTH does not repair these if the trace has been fried. The trace, while it worked, was designed too thin. Later TIUs have a substantially beefed up trace. I'd say use what channels you can on it, and hope the tooth fairy brings you a Rev L.

Chris

LVHR

To all you guy's a warm thank you. No large letters  THANK YOU. I will stick too the 3 channels, and be thankful for that.  Sonny.  Oh yes I may be able to keep my store teeth. Have birthday Oct 3rd. Letting the family know I want Gov't lettice  Then I will hit 90.   Sonny

GRJ, if a trace is burned, can't jumper wires be installed? to bypass the open portion?

I wouldn't normally expect a trace to be burned unless there was no external fuse/breaker of less than 10 amp rating.

You would think that, but for some reason MTH insisted that it wasn't possible to repair.  I didn't spend a lot of time on the issue, I use that TIU for our yard and programming track, and I only needed two channels.  I thought perhaps someone would have tried the repair, but nobody has jumped in to say they did or didn't succeed.

When, a 20 amp trace burns like that , the inductors on those channels would also short/fuse.  They are custom and not available.  So you wouldn't have a DCS signal on that channel even if you jumped the trace, IMHO. Let alone any other damage.   G

Could be, perhaps that's why they stated it wasn't repairable.  I suspect the trace wasn't really a 20A trace, which is why it cooked.

Trace is suppose to be rated for 20amps.  That is why the fuse is 20amps.  If the trace is rated at less the fuse should be rated below that value.  The issue MTH is not aware of, which I figured out on several repairs,  is the line inductor generate too much heat at high current rates and the insulation melts shorting the inductor and changing the inductance.  This kills the DCS signal.  Same on Power Supply boards.  It is not always the 4 legged small donut.  So while the fuse blows at 20amps and saves the trace, the damage is already done to the ability for the channel to send a DCS signal.  G

GGG, so why doesn't MTH use a 10-amp fuse to keep the inductor from overheating????

It was easy to exceed the 20A rating of the trace on the early (RevG) TIUs. The commons are all tied together internally. So if you were using buss wiring, you ran one common between the transformer and the TIU, and one between the TIU and the layout. But you used up to all 4 of the hot sides. If you ran 3 passenger trains with all the lights, smoke and sounds, you could easily pull close to 9A per train. That's 27A and one fried TIU. I know. I did it. (See below.)

It is much harder to do it now. The commons are now split to one per channel, each fused, and each more robust.

Chris

LVHR

Chris, that's why a common buss should never be fed through just one TIU circuit, but should be spread out among all.  In fact, on my layout, I don't feed common through the TIU at all.  All accessories and lighting are also connected to the common buss, which means common current can exceed the total of the TIU hot circuits, since lighting and accessory hot feeds of course do not go through a TIU.  The black outputs are connected to my common buss, and nothing is connected to any black input.  Gives one of the forum resident experts fits, but it does work well, so long as all wire connections are sound.

I tie all the commons together at the output of the TIU.  It may not be according to Hoyle, but it avoids any such issue.

That's a good lookin' TIU Chris, talk about Fire In The Hole!

Actually, GRJ, I think that is the most hoyliestic way to wire, since it avoids surges as wheels jump from one black circuit to another.

Well, it just made sense to me when I was doing it.

RJR, GRJ,

This incident was thankfully not catastrophic, although it could have been. I had the TIU located on the bottom side of the Power module. All of us at the show smelled something hot, but could not figure out the source, at least not right away. Fortunately, nothing caught fire. What you see is all the damage there was. But it was a close call. We were able to keep running by bypassing the TIU and running either conventional or TMCC for the remainder of the show.

When I returned home, I immediately took the module out of service and redesigned the electrical component configuration and connections. The new (and present) configuration has the TIU on the topside, out where there is plenty of ventilation and all the operators can see it. It is fused on the hot inputs, and has a heavy buss bar that ties all the commons together on the output side. The buss has a heavy external connector to the input commons, so it is highly unlikely I will ever burn another trace or blow a fuse. There are common connections on the input side, but they serve just to illuminate light bulbs on that side. The bulbs serve as readily visible confirmation of input voltage to each channel of the TIU. I have a set of bulbs on the other side serving the same purpose, as well as being the “magic” bulbs.

What I do need to do is split the commons on the output side to the tracks and beef up the connector between the two. I’m planning to use Anderson power poles.

Chris

LVHR