Rev L TIU issues

I used to be concerned about the strong smell, but once they air out for a few months, it mostly goes away.  I think it had to be something in the manufacturing process, as I bought two of mine brand new in sealed factory boxes, and it had the same smell.  The used one also had the smell.  Note that these also were manufactured in different manufacturing runs as the one PCB has a different layout than the other two.

Hi Folks,

Is there an easy way to determine that a TIU has stopped transmitting  the DCS signal?  

TIU failure would be the last place I would look if my DCS engines stopped running.  I would spend hours looking for engine failure, replacing engine batteries, track problems, wiring problems, Z4000 problems, etc., etc. before I would guess that the TIU DCS generator had failed.  

I only have one TIU and no spares on my layout.  Also, I don't know of anyone nearby who runs DCS where I could test my engines.  There aren't any O gauge shops in my area either.  I am on my own when it comes to running DCS.

Joe

Yep, when you turn on the TIU and power the track, the PS/2 locomotives will come up in conventional mode.  If it's all wired correctly, and the TIU is configured for DCS outputs, it's probably not putting out the DCS watchdog signal.

That is absolutely true Pete.  We had the problems on Variable channels that were set to fixed.  Most of the guys I have heard from with that problem were also runninng in Fixed.  I guess Joes pie chart would have to have a slice for those guys that never use it that way which is alot more than .0000001%

Hmm...  I run the variable channels as fixed so I can pop a conventional engine on the rails and test it without switching plugs.  Maybe I should rethink my organization!

 Sorry Ben.

I'm running three channels on the "L" version with one variable used as fixed for a while now(2 years??).

 I just didn't want to see guys get alarmed that there maybe something wrong that isn't. 
 

PS

The pie chart was a joke aimed at an attempt to fire me for possibly taking a five extra minute break. They blew up the break portion on the chart so that it was grossly oversized. I said, you've got to be kidding me? I can read!

That is absolutely true Pete.  We had the problems on Variable channels that were set to fixed.  Most of the guys I have heard from with that problem were also running in Fixed.

That was the issue I had with my TIU as well.  Maybe the Variable channels just weren't designed run that way.

Well, the fixed channels are just a wire from input to output, only stopping for the fuse and the power control relay.  Not much to go wrong there.  The variable channels have the drivers and electronics between the inputs and outputs, so there's lot more parts to fail.

Only MTH could truly tell us if there is a commonality with the failures, and I suspect that's not going to happen.

This is a little concerning since the DCS system I just received for Father's Day is a version L.  I guess I will make sure I ask my wife to keep the receipt. 

It looks like the variable channels may fail when in the fixed mode.  Since I plan to run two channels in passive mode, would a variable channel that has "failed" still provide the DCS signal?  If I can still get the DCS signal off a variable channel after it has failed, then the Rev L that I have that will soon be outside the warranty period will still be fully usable to me should it have problems. 

Ron

I would speculate, and I do mean I'm speculating, that passive mode would be less likely to kill the variable channels, as you're not calling on the drivers to handle any current.

John,

Sounds reasonable.  I had not given it much thought as to which channels I would use in the passive mode, but it looks like using the variable channels would be the better choice under these circumstances.  I was not sure if the variable channels still put out the DCS signal when there was no power to the input side; I need to read the TIU manual again.

Ron

All the channels put out the DCS signal if programmed to do so in passive mode.  Our club layout is currently using a TIU in passive mode with just aux power, and all the channels are in use for the DCS control.

It looks like the variable channels may fail when in the fixed mode.

I really don't believe that's a factor. My 3 Rev. L TIUs had all been in service for 2+ years with all 6 variable channels in fixed mode since day 1, and it took that long for 1 of the 3 TIU's to fail.

Since I plan to run two channels in passive mode, would a variable channel that has "failed" still provide the DCS signal?

No, it would absolutely not do so.

I have had 4 RevL TIU's operating in Super Mode that were all purchased when they first became available.  I have commented previously on this forum wondering when software will be available to fix some of the bugs (lash-up issues etc) that have been discovered when operating the Rev L's.  Any word on this?  It has been a long time!   In reading over these posts, and learning of so many Rev L failures, I am wondering if it would be immediately evident if one TIU were to fail in a group of 4 Super Mode TIU's like I have.  Would the remaining ones continue working and what would be the outcome?  Phil  

Hi Phil,

The software bugs are not specific to the Rev. L's.  They apply to any TIU running the current firmware.  I know Barry has been testing some early betas (alpha test +), so the fixes are coming.

The hardware issues with some Rev. L's being discussed in this thread manifest themselves as a loss of all DCS signal on one or more channels.  On your layout if you lost signal output on one channel that was serving part of a mainline you would see a loss of control when the train was on the track served by that channel.  The rest of the main would operate normally.

I had a RevL TIU die about a month ago...it blew a capacitor. Sent it in and they replaced about the same components...that being 2 IC chips (U502 & ??), 4 Zener diodes, capacitor and a toroidal choke. The diodes are placed on the bottom of the board across a set of leads on all 4 of the small toroidal chokes. Also has a silver dot next to the RevL sticker on the bottom of the case.

Bill came to $60.00 and MTH Service assured me that there's no problem with these..and this thread is blowing it all out of proportion.  

I am a MTH trained service tech and have repaired 2 Rev L TIUs with loss of DCS signals on single or multiple channels.  In both cases the layout did not have 10 amp fast acting fuses installed between the power source and the Rev L TIU, when a short or surge occured on the channel.  The chips indentified as U340, U341, U440 and U611 control the DCS signal, one for each channel.  The bi-drectional zener diode modification installed on the output side of each channel adds protection against future shorts and surges on the respective channel.  Techs put a silver dot next to the Rev L label to indicate the zener diode modifacation has been installed.

Great info Jim. Would installing the zeners across the output terminals achieve the same protection and if so what value zener should be used? You say bi-directional. Could you tell us the part number?

Pete

Bill came to $60.00 and MTH Service assured me that there's no problem with these..and this thread is blowing it all out of proportion.

The constant here is this:  The ability to control the engine is lost, when a Variable channel is jumpered to a Fixed channel, when this problem occurs.

This is either a design issue and/or we've been told to operate the system in a way that it shouldn't have been (jumpering Variable channels to Fixed channels in order to run command control and conventional engines from the handheld), not operator error.

When mine stopped working correctly, the only thing I was doing was letting the engine run around the layout at a constant speed, didn't even have the handheld in my hand.  There were no apparent power fluctuations, interruptions, or derailments.

Out of all these failures, have any of them been a failure of the Fixed side or have they ONLY been on the Variable side?

Should MTH be charging to fix this problem?  Should they be doing a "recall" or put out an announcement not to jumper the Variable and Fixed channels together?  When a recall to fix a design flaw in a car is made, the customer is usually not charged to have it fixed.

If the zener diode is the fix, why the heck wouldn't it be added to the design?  Or have they and they are just catching the ones not included with these mods?

I don't know of any issue connect the variable and fixed INPUTS together.  Obviously, it's a very bad idea to connect the variable and fixed outputs together!

Bob,.

The DCS signal is lost when a Variable channel is jumpered to a Fixed channel.

I can guarantee you that is completely and totally not true!!

Please do not spread rumors to that effect.

Jim, I have not had to open a Rev L yet, but the I have replaced many TVS diodes in other models.  Are you saying they are adding additional diodes?  G

Sorry Barry, statement has been edited.

 I have been running my TIU with a jumper from a fixed channel to a variable channel set to fixed, going to my engine yard. I have not had a problem with it. I have a fuse inline on the red wire from the bricks. It has never tripped yet.

I'm confused by the posts a little. Is this a bad practice?

Bob,

The ability to control the engine is lost, when a Variable channel is jumpered to a Fixed channel, when this problem occurs

That statement, although true, is extremely misleading.

When anything happens to the TIU's Fixed Channel #1, all channels, including the Variable channels, lose the ability to provide a DCS signal.

This includes all events from a tripped breaker or a blown fuse due to a derailment, to a full-blown failure of the entire TIU and everything in-between.

This is not poor engineering, rather, it's just a fact of life. Every such issue that causes only Fixed Chanel #1 to fail can be prevented from affecting the Variable channels (and Fixed channel #2, as well) by powering the TIU externally via the Aux. Power port.

Refer to The DCS O Gauge Companion 2nd Edition, pages 92-93, Part V - Advanced Features and Functions, 1. External TIU Power, for additional information.

This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site! Click on the link below to go to MTH's web page for the book!

Barry, the problem isn't with Fixed1, it's the Variable channels when configured to run as Fixed.

Both of my variable channels have lost the ability to run an engine under command control  when trying to change them from Variable to Fixed.  If I don't change Var1 or Var2 to Fixed, I can run a conventional engine from them (Var1, Var2).

I had no indication there was a problem until I tried to bring the train to a stop, it just kept running at the same speed and nothing could change it except to power down the system.

As of now, both Fixed channels can run command control engines (PS2 and TMCC) PLUS, both Variable channels can run conventional engines.  Neither Variable channel can run a command control engine by changing the channels to Fixed.

I would have thought that was "a fact of life" as well, until folks started having the same apparent problem.

There's something occurring when trying to run command engines thru a Variable channel, by altering the state of the channel from Variable to Fixed.  Seems like MTH has a fix for it, which tells me it is an engineering problem.

Bob,

There's something occurring when trying to run command engines thru a Variable channel, by altering the state of the channel from Variable to Fixed

No, that's the reason. Simply switching the channel mode isn't going to affect anything physically.

I've been running all 12 of my variable channels on my Rev. 3 TIUs for 8+ years and the only channel failure I've experienced was on one TKU's Fixed #2.

Whatever is your problem, it's not that.

There's something occurring when trying to run command engines thru a Variable channel, by altering the state of the channel from Variable to Fixed.  Seems like MTH has a fix for it, which tells me it is an engineering problem.

 

Bob,

No problem here with my H1 TIU running variable channels set at FIXED from day one.

I know some folks have had no problems with their system, but there seems to be a few that do have problems where at one time they could run command control thru their Variable channels, and now they cannot.  I can 99% guarantee you that nothing odd occurred while my train was running at a constant 10smph around my layout, other than I lost control of the engine when I tried to change speed.  1st time (on Var1) I thought was a fluke, second time (on Var2) not so much.

We know a lot of people driving Corvairs also didn't have any problems, but we all know that some did.

Barry, I don't understand your comment:

No, that's the reason

Could you please re-explain?

Bob,

Could you please re-explain?

Turning on or off a software switch is not, generally speaking, going to destroy hardware.

What's much more likely is that one of the components in the variable channel's voltage regulator circuit was latently defective and that simply adjusting the variable channel's voltage caused it to fail.

Further, assuming that both variable channels used components from the same batch, if one channel's component failed the other would most likely fail as well.

That I understand, thanks

So a few of us got TIUs that were made using components from a certain batch, those that have TIUs using components from another batch may or may not ever have this problem.

Has MTH identified the faulty batch, can I look at my TIU and determine if it was made from this batch?  Will MTH put out a notice or is it up to the individual to contact them?  My 1st failure occurred back in November of last year:

https://ogrforum.com/t...t-tiu-failure?page=1

The tech that just worked on my TIU said that only channel 1 Fixed was NOT generating the DCS signal...the remaining 3 channels worked fine.

The IC chips that were replaced on mine is U502 & U341. Also replaced choke T301 & capacitor 330. Chokes T203, 301, 341 & 802 are the ones that have zener diodes installed on the bottom and yes they are a added on item which tells me the design of the board isn't quite right..as in there's some stray voltages that need to be in check.

I was kind of surprised that MTH did charge me for this repair on a obvious design flaw. 3 years ago I sent in a REv.I3a Tiu to be fixed and MTH replaced some inductors and a IC chip free of charge...and that TIU was way out of warrantee...I guess MTH needs the $$$ more than I do these days. 

Now I'm starting to think once again about heading back into the world of DCC. If there's ever a problem with a NCE DCC booster then NCE will fix it free of charge. QSI will fix their decoders free of charge as will Digitrax, Zimo & NCE. MTH can keep their proprietary junk hardware and their expensive **** PS2 & PS3 test fixtures...I have both and have roughly $700.00 tied up in them. PS3 is a abomination as I have seen those boards and good luck with them esp. with those crappy 2x15 plugs with 28 gauge wire coming out of them.

These are also chips that a MTH tech could replace.  The ones I stay away from are the very fine pitch ones that have a fistful of leads on all four sides.  Those are a real PITA to change.  The coarser pitch ones like the buffers are easy to change, and the parts are cheap.

Bob,

So a few of us got TIUs that were made using components from a certain batch, those that have TIUs using components from another batch may or may not ever have this problem.

I was spitballing as regards the real problem root cause. I have no knowledge of any bad batch of components. That''s purely speculation on my part as a possible, reasonable cause of your problem.

I was just talking to some of the techs yesterday down at MTH, and they didn't mention bad components.  They did say that it appears that the Rev. L was a bit more sensitive to surges, which is why the extra protection diodes were added when they repair the early ones.  The new board layout apparently has those diodes.