TIU has lost 2 channels, fuses are good, but only 2 channels now work, REV L

when you get track or engine shorts it damages the 244 buffer chips inside tiu especially on the REV L model and then you loose  signal on those channels. normally they can be repaired. if you loose signal then when you power up tiu engines involved will start up in conventional that's a sign you have lost signal on those channels!

Alan

Thank you Alan, now if can only figure a way to fix this thing? Impossible to purchase a new one, at this time. Not that we all don't have far better concerns. Stay safe...

I fix TIUs. G

I'm concerned that not only the TIU but the DCS remote may be compromised. I'm getting all kinds of strange reactions from my prompts. Things like engine functions needing to be feature reset, after loosing the separate functions during operations. Can this be due to the TIU being screwed up? Do you recommend I get both the TIU and DCS remote looked at. What would be my next move, should you want to work on my stuff? Mailing, turnaround time, etc. Thank you for your response to my post. Keep safe, Lou

First step is to fix the TIU before you go chasing phantoms.  George (GGG) can fix you up with a TIU repair.  I also do them, but I have a backlog, so I'd send it to George if you're in a hurry.

Thank you John

@gunrunnerjohn posted:

First step is to fix the TIU before you go chasing phantoms.  George (GGG) can fix you up with a TIU repair.  I also do them, but I have a backlog, so I'd send it to George if you're in a hurry.

Question to you techs: Do you do a diagnostic test on said unit when received? (Check each channel for malfunction) Or precede by what owner says is a problem? Thanks,I have a couple with headaches!

I thought of purchasing a new TIU, if there are any available? Though I think there might be a big hassle setting a new TIU with my existing DCS controller? I never used 15 amp fuses on my layout, much to my regret now.

@nmtrains posted:

Question to you techs: Do you do a diagnostic test on said unit when received? (Check each channel for malfunction) Or precide by what owner says is a problem? Thanks,I have a couple with headaches!

I 'scope each channel for the DCS signal strength, and then test the variable channels for voltage control functions.  Obviously, I check if power comes through each channel, finally I verify that the aux power properly powers the TIU.

While I like to know what the user sees, I don't totally depend on that for the diagnosis of the issue or issues.

Hello John,and thank you for your response!

Hey GGG/GRJ...

I have a question out of pure curiosity. Are there ever any physical indications on a TIU's circuit board (that are easy to see) that shows its been damaged?

No external physical indications.  For the Rev. L TIU's, it seems the 74ACT244 suffers gate failures from transients which weakens the DCS track signal.  Four outputs are paralleled for extra signal strength, and the failure manifests itself as one or more gates internally failing.  When that happens, the DCS track signal amplitude is reduced.  As more gates fail, the signal gets lower and you start seeing control issues, failure to add engines, etc.  Earlier versions of the TIU don't seem to have the same issue, or at least not nearly as often.

John, it seems that this product is doomed to failure no matter what we do to keep it going? I've been thinking about getting a new TIU but they are all Rev L.  I hope MTH comes up with something in the future that will eliminate these issues. Those of us who enjoy and operate MTH do not have much chose in the matter. Thanks for sharing your expertise.

Yes some times you can see a physical damage.  Usually not.  Each channel has to be tested for transmit and receive.  So it is time consuming, let alone a bad channel can effect others.  So knowing how the TIU was operated and what failed is important to the repair approach.  Otherwise chips come off trying to figure out which one is causing issues, especially if no channel working.  Some times that is just one bad channel effecting them all.  G

With future issues possible with my current TIU – It seems now that my best choice is to purchase a new TIU. Seeing how that there aren't any MTH TIUs available for the foreseeable future, I've been thinking of cutting off my third loop, (disconnecting the crossover) and using either a conventional  Z-750 transformer with a Z-1000 brick, or even, if any available, a DCS Commander unit. I would still have 2 channels left on the TIU to run the other 2 loops and a separate DCS Commander or conventional loop. Should the TIU die completely, I would have to go old school with everything. This isn't ideal, but I would be able to have some trains running while waiting for the better solution of obtaining a new, and hopefully, improved MTH TIU.

By having the ability to run some trains, this would also give me time to get the current TIU fixed by George (GGG) – if you are willing to take this on George?

I would greatly appreciate any thoughts that anyone has on my temporary solutions. Thanks once again to all for the great advice on this string.

Biglou, there are no problems that result from old & new remotes working with TIUs.  I have original issue Rev G TIUs & remotes, and latest Rev L TIUs and remotes, and all work happily with each other.  All have been upgraded to latest versions of software.

If you're running DCS, there is no reason why you can't connect two loops to the same TIU output.  I have done it when a TIU failed and one of my others wasn't readily available.  You might be limited on the number of traisn you can run at one time.

RJR, I was running 3 loops on three separate TIU channels. One channel wasn't used at all. The first channel failed so I used the remaining 3 channels. All channels were set up as fixed channels and all track loops were connected properly through crossovers. When a second TIU channel failed, I 'm now using the two remaining channels. I use an MTH 500 brick to power the TIU and 3 separate MTH 1000 bricks that are connected to lockons through the TIU to each separate loop. Now that a second TIU channel has blown, I'm going to disconnect the the track to the inside loop and run either conventional or with a DCS Commander unit, should one be available, on the separate loop. I'll continue to run the 2 TIU loops together, as long as the TIU holds up. It's a temporary solution, until I can either get the TIU repaired, or can purchase a new TIU, if and when they are available.

Thank you for your help in this matter. Best regards, Lou

@Biglou posted:

"It's a temporary solution, until I can either get the TIU repaired, or can purchase a new TIU, if and when they are available."

They available now at many shops, separate or with a remote.

Sure my e-mail is in my profile.  G

@gunrunnerjohn posted:

 For the Rev. L TIU's, it seems the 74ACT244 suffers gate failures from transients which weakens the DCS track signal. 

I would expect usage of TVS diodes would prevent this failure mode?

Apparently not as the TIU already has a TVS component for each channel.

BobbyD, Unfortunately I have not been able to fined any new or used TIUs. Do you, or anybody know of anyone still having them for sale?

Try checking to see if the connections inside the TIU are loose.   If you open it up there are nuts that hold the connections in place.   Sometimes they loosen up because you turn the outside terminals to hold the wires in place.    

@Biglou posted:

BobbyD, Unfortunately I have not been able to fined any new or used TIUs. Do you, or anybody know of anyone still having them for sale?

Just go to the MTH Product Locator and then select "Find It Locally" for that item. There are currently 6 vendors for the 50-1001 Set. Probably more as many dealers don't take advantage of the opportunity. And 11 for just the 50-1003 TIU alone.

@Biglou posted:

BobbyD, Unfortunately I have not been able to fined any new or used TIUs. Do you, or anybody know of anyone still having them for sale?

Also you might want to check the forum sponsors first to see if they have the TIU. This way you can support the forum and OGR while making your purchase. Having said that I just checked 4 sponsors for you and none of them had it. I checked Mr.Muffins, Mario's, Nicholas Smith, and Pat's. I hope you find one.

Back when I was in 3 rail I had fuses on my TIU. It was very annoying and not to mention costly as almost every derailment blew the fuse. I was always replacing fuses. If it were me I would go with some type of circuit breaker and make it 10Amp not 15Amp.

Thanks all for all the great advice. I'm going to try the MTH product locator to see if it works out. Also, I did check the guts of the TIU, fuses were fine and no loose nuts. Thank you Phil for checking things out so thoroughly. All the best to you guys.

@bmoran4 posted:

@gunrunnerjohn posted:

 For the Rev. L TIU's, it seems the 74ACT244 suffers gate failures from transients which weakens the DCS track signal. 

I would expect usage of TVS diodes would prevent this failure mode?

@gunrunnerjohn posted:

Apparently not as the TIU already has a TVS component for each channel.

 Isn't the TVS Diode on the output of each channel? Would they be minimally effective against transients entering the TIU inputs?

Not sure exactly where the TVS is placed in the circuit, but I refer you to Adrian's rather extensive analysis of the problem, and it ain't as simple as you might imagine.   If only it was as simple as sprinkling a few TVS devices around...

Weak DCS signals, Failed TIU Output Drivers, and Design Solutions devloped under collaboration between AGHR and MTH