Rev L TIU channel Failed

Rick, 

I had a similar issue with my Rev L TIU back in December. I traced the issue to a faulty TVS diode. You can test this with a multi-meter or by removing the suspected culprit and powering up the TIU with the TVS disconnected. I was able to replace to the TVS for just under $5 (including shipping).

Thanks for your quick reply.  

I have very little background in electronics repair so a few questions.  The TVS diode, how do I identify it, and how is it removed and replaced?  Also, where would I purchase one from?

I was really surprised that a derailment led to this failure.  would it be a good idea to replace the 20 amp fuses inside the TIU with 10 amp?

 Shouldn't he move his inline fuses to the input side for better protection???

I agree.

So do I. The power surge would have to go thorough the 10 amp fuse first before getting to the TIU. Anyway a little late now but these things happen to all of us

Having the fuse at the output of the transformer ensures everything down stream is protected.  If the fuse was at the track connection only a short at the track would blow the fuse.  Transmission lines, TIU fault, or wire between TIU and transformer would not be protected.  This is all about an over current protection.  So I agree a fuse on the output of the transformer is the best over current protection.

The TVS is voltage spike protection.  Regardless of the fuse position I am not sure that would have prevented this, since the short occurred at the track, and fuse blew.  G

All of the replies have been very helpful and reassuring, since going to MTH for the repair would be time consuming.  A friend of mine with an electronics background tested the TVS for Fixed One.  Failed open.  Explains all of the failing fuses.  I'll go to Digikey as recommended by Gunrunner, and my friend will replace the defective TVS.

Question: What would prevent the DCS Watchdog signal form being present after the TVS is replaced?

The TVS test open when good. You have something else blown, maybe a chip.

I'm curious how he tested the TVS.  They will normally appear as an open circuit until the rated voltage is reached.  Also, if it's open, it should effectively be out of the circuit.  It won't be providing protection, but it also shouldn't affect operation.

Gunrunner.

I probably mixed up my terms, as you are correct that it would have been closed, leading to the blown fuses.  I'm learning.

Just ordered the TVS from Digi-Key.

Shorted I'll buy, that would indeed result in the exact symptoms you see. 

Rick K,

   I think you need to determine just what caused your initial problem, having owned and operated a DCS for many years, I have not seen this happen in this manner before.  It does not sound like the track short actually caused your problem, this actually looks like you had a short that started inside your TIU for some reason, not external on the rails.   I would be careful when you go back into operation after replacing the TIU parts, that your problem does not resurface again.  Maybe gunrunnerjohn & GGG can give you some further guidance.

PCRR/Dave

Dave,

It was a short on the tracks that was the root cause of the problem.

Unfortunately, he had the fuse between the TIU and the tracks, rather than between the transformer and the TIU. That's most likely the reason the channel went.

IF it's just the TVS, no serious harm done.  However, if you don't have any DCS on that channel, then there's some chips to replace on the board.

Thanks again for all of the support.  I will take Barry's suggestion and install a 10 amp fuse between the Z1000 and the input side of the TIU.

Separate question.  If the TIU's maximum amperage per channel is 10 amps, why are there 20 amp fuses inside the TIU for each channel?  As an additional protective measure, should I replace the 20 amp fuses inside the TIU with 10 amp fuses?

I think  each channel  will probably handle a little more than 10 amps however 20 amps is probably over the limit. You don't want to have to take the tiu apart to change a fuse so I would leave the 20 amp internal fuse. We have 4 tiu with 10 amp    32 volt glass  fast blow fuses. We do go through a few fuses  but haven 't lost a tiu over the last 10 years or so... we still are still using a original "G" from 02 . (10 amp fuses  between post war ZW and TIU input)

Yes a  built  in tiu circuit breaker might be the answer.

The 20 amp fuses are just there to protect the traces on the board as far as I know. You can't repair them I don't think. The TIU channels are only rated for 12 amps maximum. That's why you need the fuse between the transformer and TIU unless you have a fast electronic breaker in your transformer.

20 Amps protects trace in the TIU.  Using 10 amps external and leave the 20 amp alone.  G

Rick K,

   From what Barry is saying you definitely need to do more reading and set up your fuses or breakers in the correct manner before you ever try to power up your layout again. After reviewing the entire thread Barry is correct, it was the short that caused your problem, because you were set up incorrectly.  You may have damaged more of your TIU than you think, if you are lucky you will just replace what has been talked about, if not like gunrunnerjohn says you will have more repairs to do.  I recommend the Scott type 10 Amp breakers between your Transformer and your TIU, they work really well, follow Barry's example in the book as you set up, if you have trouble, review the OGR Video Guide to DCS, Rich does a great visual instruction job, on showing how to properly set up your equipment.

PCRR/Dave  

Rick, So when Joe, Joe, Gregg, and I said to move the fuse, when Barry says it, it is time to move it....

Dave,  it is really hard to say if the fuse on the other side would have made a difference.  The fuse was in a fine spot to protect the track.  The short was on the track and the fuse blew.  If the fuse was on the output off the transformer it still would have blown, but the spike was still present.

First, some z-1000s seem to have really slow or bad breakers so they don't seem to protect anything. 

Most likely when the fuse blew and the spike occurred the TVS shorted.  Otherwise the 20 amp would not have blown too.  Having the fuse on the output is the reason the TIU fuse blew.

When the TIU TVS Shorted, the only thing left to protect the TIU and the Brick was the Brick fuse.  It did not trip and the 20amp fuse in the TIU blew.

If the fuse was on the output of the transformer it would have blown first, I still think the TVS shorted, but there would be no power to TIU.  When Rick replaced the fuse and tried it a second time, his 10amp fuse would have blown again. At which point he would realize he still has a problem.

G

I'm not a fan of the Z1000 bricks, or their lower powered brothers.  I've seen far too many that have breakers that are either too slow or simply defective.  There have been a number of stories about popping the TIU fuse and not the Z1000 brick fuse, even without a shorted TVS.

Oh, and I agree with all the other folks, better circuit protection between the TIU and the transformer seems clearly in order.

Based on the advice received from all respondents, and in an effort to keep peace in the Family, I now have a 10 amp fuse between the Z1000 and the TIU, and a second 10 amp fuse between the TIU output and the track.

If this doesn't solve the protection problem, then at least I have the TIU surrounded.

Rick

As the fuse on the output didn't blow in the first place, I can't see leaving it there. I believe you should move it to the common between the transformer and the TIU if you want to feel safer with 2 installed.

Rick,

and a second 10 amp fuse between the TIU output and the track.

That fuse is completely unnecessary. It serves no purpose.

Rick,

    gurunnerjohn uses finesse when he tells you he is not fond of the Z1000 Brick,

let me say it real plain, get rid of the Z1000 brick.  Some guys like the bricks,

I do not own one myself, and doubt I ever will, especially the Z1000 brick.

Good luck with your set up.

PCRR/Dave

The major problem with all those bricks is the breakers, you just have to add protection if you want to use them.  The 10A fuse between the brick and the TIU is the answer.

If it turns out to be the TVS, I posted some photos of  how I did the replacement process a while back. You can find it here. Also a bit there about identifying the bad one. Hope it helps.

Fred 

Fred

Thank you.  Yes I found your thread on Friday morning and the pictures and description allowed me and an electronics repair savvy friend to identify the failed TVS.  With your info and the link from Gunrunner I was confident when ordering the replacements from Digi-key, a company I would not normally do business with (they gave me the option of retaining my personal and credit card info on their secure server, an option I've never been presented with before).

The discussion about where to place inline fuses led to installing the 10 amp between the Z1000 and the TIU (In addition to the 10 amp already between the TIU and track).  With my small layout the Z1000 is a practical choice, but I've only seen its circuit breaker trip once, a lousy record of protection.

As a diversion but a somewhat related question, would any of the fuses be necessary if you were to use Lionel power bricks with the TIU?

At least in the command environment, fwiw, I have found the Lionel brick circuit breakers are very sensitive, and I mean this in a good / complimentary way.

You would not need fuses if you used either Lionel bricks or their TMCC lockon. They will trip in less than 10ms which is much faster than any fuse.

Pete

Make sure you're specific about the bricks, the PowerHouse 180 bricks have the excellent electronic breakers, the PowerHouse 135 bricks have thermal breakers very similar to the Z1000 supply, you need fuses for those!

Pete, note that the TMCC Direct Lockon is most certainly NOT DCC compatible.  When you connect it between the TIU and the track, PS/2 locomotives cease to function.

Rick, Digikey is a reputable outfit, and I've had my card on file with them for years.  I breeze through with my orders in a flash.   FWIW, I don't think you need a fuse on either side of the TIU.  If you have one between the transformer and the TIU, that is sufficient.

John, the question was about using fuses or bricks between the power source and the TIU. I assumed he was referring to 180 watt bricks. I understand only passive devices should be placed between the TIU and track.

My test track consists of a Post War LW transformer connected to a TMCC Lock On which is connected to the TIU which connects to the track. No problems in 5 years which included many derailments.

Pete

The TMCC Direct Lockon before the TIU might not affect the signal, or at least it shouldn't.  However, after seeing it's effect on DCS at the track, I decided I didn't need them in the picture.

I was unaware of this. Thanks, I'm unplugging and going to Radio Shack for items to put inline fuses in. I thought the 135 did have the protection. I been lucky. Thanks

The PH135 has a breaker, but it's not all that effective.  It takes seconds to trip, even on a significant overload.  I've moved to 100% PH180 bricks for my "brick" power, and that's all we use on our modular club layout as well.

Gentlemen,

   If you choose to use a brick use the PH180 and put Scott 10 Amp breakers between it and your TIU, the PH180 has the most sensitive breaker on the market today, I do believe it is an electrical breaker of some type, and I still recommend the Scott Type 10 Amp breakers also to fully protect your TIU.  I would rather use an old Lionel ZW or KW transformer with 10 Amp breakers where you can vary the voltage input, than any of the other bricks on the market today.

PCRR/Dave