Adrian, Thank you for describing this problem and your club's remedy. I think the information was presented well for a person who has some basic electronics knowledge.
The TVS on the output of the TIU is a much higher value than needed to protect the 244 signal driver chip, those TVS chips are 9V rating. Also, Adrian said what I've said about the TVS across the power supply when protecting the electronics in the engine. That's good, but having it right across the engine pickups in the engine and close to the actual electronics is simply better.
In the case of the TIU signal generators, I was looking at what could be done to make the protection boards more compact. I wonder if two back-to-back 8V Zener diodes and the 9V TVS would be a good solution. The exact Zener voltage could be "tuned" to balance the protection for the TVS so it doesn't have to absorb the power of a longer surge. The TVS will do the initial suppression, and if the spike lasts long enough, the Zener diodes carry the load. This would seem to be similar in concept to the diode arrays, but a far lower parts count. It might be possible to get the board size down to a very compact little board with a small enough parts count. I'm thinking about .3" x .5" or so. This kind of board could really sit right on top of the 244 chip and just solder directly to the leads. It would be easy to install, and there's tons of clearance on the top of the TIU circuit board.
Thanks Adrian....I was able to understand just enough of this to see that you have likely hit on a permanent solution for DCS signal degradation. I'm running out of good channels here.
Could I possibly be smelling ozone over at GRJ's workbench as he conjures up some sister boards for public consumption? One ERR door closes and another opens. 
Bruce
Adrian,
Our club has a conglomerate of knowledge, but this has opened a new channel to help remedy the degradation of the signals, and that dreaded "Engine not on the tracks" readout. We run 5 TIU's with scads of AIU's for the layout.
GRJ, Will the fix your contemplating blend with the TMCC booster to make both systems better?
The TVS are after the transformers where the power and digital signal are split up, so TMCC/Legacy systems won't even notice them in the system.
Maybe it would be easier to lift off the ACT244 and put the adjusted board underneath between it and the main board.
Honestly, my thinking:
I know this sounds a little bit out there... but I think if a club is willing to spend $1000 on TIUs, probably $1000 on remotes, $500 WIUs, and maybe another $500 on power supplies, plus maybe another $1500 on Legacy/TMCC support and like who knows how much on the trains themselves...., then it makes sense to spend $250 to get a good club oscilloscope to debug the DCS setup. If you don't know how to do that, you can watch a 12 minute youtube video on how to make the measurements. Heck, if there's interest I can even make the tutorial video and post it here. I think if you learned how to change train tires, replace a smoke unit, or wire up a layout, then the signal measurements aren't really that much more to know. It took me 1 hour to change a tire yesterday.
I've found trying to troubleshoot DCS without looking at the signal on the scope isn't effective, it either works, or doesn't work. Different trains behave a little different. You can't really separate the RF link issues from the track signal issues and everything is very anecdotal ("my train does this but when I do that it does that"). I always think it's better to attack this stuff analytically with measurements. Short CDMA exchanges like horns need about 5-6V to be decoded successfully. Long CDMA exchanges like adding engines need about 10V to decode. Once you drop scope probes and measure you know exactly what's going on. Also I like having it disconnected from the layout so it's not influenced by who's train is where and what amount of track is on each channel. It's just a simple direct assessment of the circuit performance.
I certainly admire all of you folks that have the patience and knowledge to stick with these things and then actually find a solution! WE are very lucky to have you all here on the OGR forum to help the rest of us (me anyway) lesser qualified folks that still like to try and keep up. It also helps the rest of us (again, me anyway) at least learn a little bit about some of these things. And I enjoy following along even if it is all over my head.
Thanks for all your efforts and please continue!! This was a neat discovery that I'm sure will help many people in the hobby.
I am confused. Are you saying that a failed TVS degrades the DCS signal and that by replacing the TVS or replacing the TVS with your new board fixes the DCS signal problem?
Or, are you saying that the failed TVS has allowed the DCS signal transmitter to become fried? The fix is to replace both the signal board and the TVS.
NH Joe
I remember Ben at the NJ highrailers was telling me that when they first got the REV L TIU they were blowing them up left and right. They gave up on the L and went with older models. Wonder if this is the same issue. Correct me if I’m wrong NJ?
is this a issue with only larger layouts with large power supplies? Knock on wood, no issues wth my REV L TIU.
Well, Adrian's fix certainly seems to hold out promise for TIU signal degradation, and the TMCC Booster should do good things for TMCC/Legacy, so I guess the answer would be yes. 
I'm waiting on Adrian's take on my latest idea, I think the standard Zener diodes should work, they're used in continuous service for power supplies, so they ought to handle a longer spike.
Adrian! posted:The TVS are after the transformers where the power and digital signal are split up, so TMCC/Legacy systems won't even notice them in the system.
Maybe it would be easier to lift off the ACT244 and put the adjusted board underneath between it and the main board.
An interesting thought. I'd just buy new ACT244's and build the boards, then arrange for the board to be soldered to the pads. There are some neat adapters that would solder onto the main board and you could plug the adapter with the ACT244 and the diodes and TVS on them into the adapter. If any issue arose with signal generation, plug in a new daughter board. Interesting thought...
New Haven Joe posted:I am confused. Are you saying that a failed TVS degrades the DCS signal and that by replacing the TVS or replacing the TVS with your new board fixes the DCS signal problem?
Or, are you saying that the failed TVS has allowed the DCS signal transmitter to become fried? The fix is to replace both the signal board and the TVS.
NH Joe
The TVS is supposed to protect the DCS transmitter (ACT244) but when it fails it shorts the DCS transmitter output so nothing comes out the TIU port. If it stays like this too long it kills the ACT244 itself
superwarp1 posted:I remember Ben at the NJ highrailers was telling me that when they first got the REV L TIU they were blowing them up left and right. They gave up on the L and went with older models. Wonder if this is the same issue. Correct me if I’m wrong NJ?
is this a issue with only larger layouts with large power supplies? Knock on wood, no issues wth my REV L TIU.
Just like us. That’s how this all started. 14 TIUs in 2 months. I get it’s the same problem. It really has not much to do with the layout, more about how rough you are on it.
gunrunnerjohn posted:Adrian! posted:The TVS are after the transformers where the power and digital signal are split up, so TMCC/Legacy systems won't even notice them in the system.
Maybe it would be easier to lift off the ACT244 and put the adjusted board underneath between it and the main board.
An interesting thought. I'd just buy new ACT244's and build the boards, then arrange for the board to be soldered to the pads. There are some neat adapters that would solder onto the main board and you could plug the adapter with the ACT244 and the diodes and TVS on them into the adapter. If any issue arose with signal generation, plug in a new daughter board. Interesting thought...
The zeners should work if you get the turn on voltage just right. You might want to test a bit. One thing to remember is the voltage varies a bit from part to part on the ACT244s so Yu don’t want to be clipping their outputs. I found soft turn on around 8-9V and hard turn on about 9.2-9.5V covers all the cases I’ve seen. Just make sure the zener you pick is 1 ns range recovery time.
You could even do a daughter board with the 244 on a socket for quick changes if something ever goes wrong later.
Adrian, with reference to your post above about a club that spends all those $$ should be willing to buy and use an oscilloscope. I am not in a club, and $250 would stretch a bit, but can you recommend an oscilloscope that a reasonably proficient person could, with a little research learn to use for this purpose?
Can these also be used with the tiu attached to the layout? I wonder if it would help to to discover spurious signals that cause the Doubletoot Syndrome?
RJR posted:Adrian, with reference to your post above about a club that spends all those $$ should be willing to buy and use an oscilloscope. I am not in a club, and $250 would stretch a bit, but can you recommend an oscilloscope that a reasonably proficient person could, with a little research learn to use for this purpose?
Can these also be used with the tiu attached to the layout? I wonder if it would help to to discover spurious signals that cause the Doubletoot Syndrome?
The one I linked in that post is about the cheapest one that can see the dcs waveform reliably. In terms of use its not that hard once you understand how to trigger properly. I can do a post on that later.
You can certainly sense the signals when connected to the layout and it’s helpful for all kinds of debugging.
When the TIU is connected to the layout the signal voltage depends on the number of engines on the track and types and such.... so when testing the TIUs themselves I disconnect them so the test conditions are identical week to week
The other thing is, there may be a bit more leeway in picking values. It's quite possible that you could get away with different values for the spike suppression and still protect the drivers sufficiently. After all, the voltage amplitude is a big driver here, the higher the amplitude, the more energy that would be hammering on the 244's.
I think this would have to be tested in a high traffic club layout to really zero in on the ideal solution.
In thinking about the outputs of the ACT244, there's no reason that the output should go significantly below ground, AAMOF, that's probably bad for the chip. That being the case, it might makes sense to try to clamp the output from going below ground and just deal with the positive swing. The absolute highest voltage the outputs should see, at least according to the data sheet is a supply voltage of +7VDC, and the output shouldn't ever exceed VCC by any major amount.
I don't know much about the circuit in the TIU, but my understanding is the four outputs of the ACT244 are paralleled to drive the signal injection transformer for the DCS signal. In looking at your scope signal, that's clearly not right on the ACT244, but rather looks to be on the other side of the signal transformer. However, we're trying to nail the surges at the ACT244 gates directly, right? Maybe the clamping can be a bit different, given the limits that the part is supposed to tolerate. Truthfully, the ACT244 isn't really designed to be an analog driver, probably why it doesn't excel at the task.
I'm just wondering if there isn't a much simpler solution here. As far as the TVS, how about forgetting the silicon diodes and just putting one of the big honkin' 3kw TVS diodes right across the gates and dispense with the diodes. It'll take a much bigger beating than the 500W ones that you were testing with, and with the adapter board, it should be easy to piggyback on the existing ACT244. I'm thinking of something like this Littlefuse SMDJ7.0CA. Hard to believe it couldn't stand up to a fair amount of punishment. It's small enough to perch right on top of the ACT244 on a little PCB.
very interesting that "MTHRD" has not responded.
if our trains would have such an issue we would demand the manufacture take it back and fix it.
why can't MTH take the TIU's back and fix them???
Adrian,
First, let me say Thanks for all the hard work you have put in to figure out what is happening! Not to mention your clear- to- the - layman explanations. I get it, or at least enough to appreciate what you have done and follow along with what you and GRJ are discussing. (Dang! That's scary!)
You posted this earlier regarding o-scopes:
Heck, if there's interest I can even make the tutorial video and post it here.
Heck, YES! I'm interested. In fact, I have an o-scope and just need to learn how to properly use it. I'll post make and model a little later. So carry on! I will keep watching and learning.
Chris
LVHR
Adrian, I've been getting some of our club members to read this post, as we ongoingly have to crawl around under the layout and use some sort of little lights that are suppose to fix all of the Woes of the MTH TIU Signal strength. Everytime that we take the layout apart to take to another train show there is always some sort of VooDoo that we have to do. It sure isn't a plug and play...From what I've read on your post you have take the time out of your busy, and did the troubleshooting and found the fix. Maybe Gunny will come up with some sort of board or whatever to make the fix simple for us simple people. I myself like Plug and Play, not Reinventing the **** wheel everytime I want to run trains. Our resident Electrical Engineer has done a great job in making what we have better, but it's a long way from the old Lionel TMCC , and now with Gunny John going to make a Signal Booster for the TMCC/Legacy that should put all of the planets in alignment. I commend you sir for your efforts and resolve..........................................................Eric Brandenburg
If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
not sure you have the correct club mentioned.
ADRIAN! is from the angels gate Hi-railers which is outside long beach calif.
However the san diego 3 railers is having the same issue.
bigdodgetrain posted:very interesting that "MTHRD" has not responded.
if our trains would have such an issue we would demand the manufacture take it back and fix it.
why can't MTH take the TIU's back and fix them???
So the thing is MTH makes great trains that generally run very well. There's no way you can expect them to find this because unless you have a club full of people and trains coming and going and derailing over and over week after week, how would you even know it's an issue? So far it takes like 1-2 weeks before these TVS diodes even start to fail in our club, and MTH has a business to run and parts to repair so it's not like they can sit there and run trains for weeks on end doing robustness tests. I'm glad I was able to help them out with that so we all benefit.
At the same time, we have a big club, and a lot of junior users that are a bit hard on the layout so we have a real problem with the TVS devices dropping out (and I'm sure other clubs are similar) so we needed a solution. Now we have an understanding of the problem, a way to detect/diagnose it, and a solution (with GRJ and others thinking about taking the work done so far and making it better). Everyone has access to this detailed write up and history of the thoughts so far. What could be better?
gunrunnerjohn posted:The other thing is, there may be a bit more leeway in picking values. It's quite possible that you could get away with different values for the spike suppression and still protect the drivers sufficiently. After all, the voltage amplitude is a big driver here, the higher the amplitude, the more energy that would be hammering on the 244's.
I think this would have to be tested in a high traffic club layout to really zero in on the ideal solution.
In thinking about the outputs of the ACT244, there's no reason that the output should go significantly below ground, AAMOF, that's probably bad for the chip. That being the case, it might makes sense to try to clamp the output from going below ground and just deal with the positive swing. The absolute highest voltage the outputs should see, at least according to the data sheet is a supply voltage of +7VDC, and the output shouldn't ever exceed VCC by any major amount.
I don't know much about the circuit in the TIU, but my understanding is the four outputs of the ACT244 are paralleled to drive the signal injection transformer for the DCS signal. In looking at your scope signal, that's clearly not right on the ACT244, but rather looks to be on the other side of the signal transformer. However, we're trying to nail the surges at the ACT244 gates directly, right? Maybe the clamping can be a bit different, given the limits that the part is supposed to tolerate. Truthfully, the ACT244 isn't really designed to be an analog driver, probably why it doesn't excel at the task.
I'm just wondering if there isn't a much simpler solution here. As far as the TVS, how about forgetting the silicon diodes and just putting one of the big honkin' 3kw TVS diodes right across the gates and dispense with the diodes. It'll take a much bigger beating than the 500W ones that you were testing with, and with the adapter board, it should be easy to piggyback on the existing ACT244. I'm thinking of something like this Littlefuse SMDJ7.0CA. Hard to believe it couldn't stand up to a fair amount of punishment. It's small enough to perch right on top of the ACT244 on a little PCB.
Uh some details. The scope is looking at the output side of the transformer, not the waveform right at the clamping device/ACT244 driver output pins. Clamping from 0 to 7 volts could work but again it's got to be quick quick quick. A small zener or TVS is faster than a big zener since Cj is the dominant term in the time constant which grows with anode area.
Maybe a small TVS in parallel with a big TVS?
GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
Hi there,
I thought about this too....
Doing a LED that illuminates when the TVS shorts is not easy since under normal condition there is sometimes no voltage there.
Think about the Thevnin equivalent..... when the ACT244 driver is outputting a "0" the voltage across the TVS is 0V, the same condition as when it fails.... so you would need to distinguish the two conditions from each other. The only way to do this is the TVS current:
Normal 0 TVS voltage 0V TVS current 0mA
Normal 1 TVS voltage 7V TVS current 0mA
Fail TVS voltage 0V TVS current high
So you'd have to put something in series (a current sensing resistor) which isn't so simple. First you need to make the resistor big enough that you can develop a sensing voltage you can collect with a diff amp, but that resistor itself defeats the protective action of the TVS since you're adding an RC pole at Rsense X Cj and increasing the turn on time.
I think a better way is to build something that senses the channel outputs with a high-pass filter, maybe about a 100 KHz cutoff frequency (so it only looks at the DCS signal). Then use some type of hysteresis comparator and digital latch to see if you are exceeding 7V occasionally. A good way is a 1-shot timer circuit. So everytime you see >7V... you trigger a one-shot that flashes the led for maybe 1 second. That way every-time a packet goes by, you get a LED flash. If the DCS excursion voltage is too low.... then the LED stops flashing.
I don't know about anywhere else so I can't speak to how common the TVS devices are, or how often they fail outside our club, but from what I've measured at least in my club, low DCS excursion is the root cause for almost all of our control problems. Some members have brought Rev L TIUs from home recently bought and installed and I've found the same TVS failing also.
bigdodgetrain posted:GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
not sure you have the correct club mentioned.
ADRIAN! is from the angels gate Hi-railers which is outside long beach calif.
However the san diego 3 railers is having the same issue.
Yup I'm from the angel's gate Hi-railers' club in San Pedro. It's like a big test-bench. At one time I thought about joining the San Diego club but don't tell anyone though.
Adrian! posted:bigdodgetrain posted:GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
not sure you have the correct club mentioned.
ADRIAN! is from the angels gate Hi-railers which is outside long beach calif.
However the san diego 3 railers is having the same issue.
Yup I'm from the angel's gate Hi-railers' club in San Pedro. It's like a big test-bench. At one time I thought about joining the San Diego club but don't tell anyone though.
if you fix our issue I will make you a deal you can not pass up!
Adrian! posted:bigdodgetrain posted:very interesting that "MTHRD" has not responded.
if our trains would have such an issue we would demand the manufacture take it back and fix it.
why can't MTH take the TIU's back and fix them???
So the thing is MTH makes great trains that generally run very well. There's no way you can expect them to find this because unless you have a club full of people and trains coming and going and derailing over and over week after week, how would you even know it's an issue? So far it takes like 1-2 weeks before these TVS diodes even start to fail in our club, and MTH has a business to run and parts to repair so it's not like they can sit there and run trains for weeks on end doing robustness tests. I'm glad I was able to help them out with that so we all benefit.
At the same time, we have a big club, and a lot of junior users that are a bit hard on the layout so we have a real problem with the TVS devices dropping out (and I'm sure other clubs are similar) so we needed a solution. Now we have an understanding of the problem, a way to detect/diagnose it, and a solution (with GRJ and others thinking about taking the work done so far and making it better). Everyone has access to this detailed write up and history of the thoughts so far. What could be better?
"what could be better"
the issue fixed.
lehighline posted:Adrian,
First, let me say Thanks for all the hard work you have put in to figure out what is happening! Not to mention your clear- to- the - layman explanations. I get it, or at least enough to appreciate what you have done and follow along with what you and GRJ are discussing. (Dang! That's scary!)
You posted this earlier regarding o-scopes:
Heck, if there's interest I can even make the tutorial video and post it here.
Heck, YES! I'm interested. In fact, I have an o-scope and just need to learn how to properly use it. I'll post make and model a little later. So carry on! I will keep watching and learning.
Chris
LVHR
A good start would be this very old post.A second one with a lot of useful details is this post where other people performed the same measurement.
Depending how deep you want to go into DCS there's a lot of other posts I've put up over the last year or so with all the ugly details
This tutorial describes the encode/decode process: DCS packet format
This tutorial describes how to capture DCS packets: DCS Capture
This tutorial describes how to transmit: DCS_transmit
This is a more analytical one that fully describes the track signal between the train and the TIU in exact detail (I think no one reads this stuff): DCS signal
bigdodgetrain posted:Adrian! posted:bigdodgetrain posted:GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts. While the design is meant to prevent the TVS shorting rapidly, I am sure after enough hits even the new one will short. Since it doesn't show up as a power short, like the input/output TVS, but will degrade DCS signal (which might not be detected on a small layout) a LED would be nice. It must be serviceable easily also.
Lastly, there are plenty of REV L TIU out there with out this TVS mod form MTH. Therefore your TIU is not susceptible to this exact failure. Your failure will be the Transmitter chip.
Most people do not have the issues this San Diego club has. I have repaired plenty and they have not come back. Frankly, I probably only worked on a few (less than 5), that had the TVS mod.
So the sky is not falling. But this mod may make the Rev L TIU much more robust. G
not sure you have the correct club mentioned.
ADRIAN! is from the angels gate Hi-railers which is outside long beach calif.
However the san diego 3 railers is having the same issue.
Yup I'm from the angel's gate Hi-railers' club in San Pedro. It's like a big test-bench. At one time I thought about joining the San Diego club but don't tell anyone though.
if you fix our issue I will make you a deal you can not pass up!
I think step one is to establish that weak signals really are the issue you are experiencing. San Diego is not *so far* so maybe I can pay a visit with my test gear and have a look for you. The TIU you have is a Rev L with the USB port on the side right?
Adrian! posted:So the thing is MTH makes great trains that generally run very well. There's no way you can expect them to find this because unless you have a club full of people and trains coming and going and derailing over and over week after week, how would you even know it's an issue?.... I'm glad I was able to help them out with that so we all benefit.
....Now we have an understanding of the problem, a way to detect/diagnose it, and a solution (with GRJ and others thinking about taking the work done so far and making it better). Everyone has access to this detailed write up and history of the thoughts so far. What could be better?
You have done an excellent job with this bit of problem identification and solving, Adrian! It's all way above my head, but I have truly enjoyed reading this thread and learning about how you approached both the problem and the solution. Very nice work!
So MTH designed, manufactured, and sold a device that self-destructs over a short period of time, intentional or planned obsolescence. but I dont see product liability as there is no resulting personal injury or property damage.
however I do see a whole lot of bad press unless MTH RECALLS ALL TIUs Rev L and fixes them.
AlanRail posted:So MTH designed, manufactured, and sold a device that self-destructs over a short period of time, intentional or planned obsolescence. but I dont see product liability as there is no resulting personal injury or property damage.
however I do see a whole lot of bad press unless MTH RECALLS ALL TIUs Rev L and fixes them.
Come on, this is not even a reasonable statement. Go back and read what was said, a large club with heavy and hard use with constant derailments and shorts. Causing degradation over a few weeks. Not your average home layout. G
Allan Miller posted:Adrian! posted:So the thing is MTH makes great trains that generally run very well. There's no way you can expect them to find this because unless you have a club full of people and trains coming and going and derailing over and over week after week, how would you even know it's an issue?.... I'm glad I was able to help them out with that so we all benefit.
....Now we have an understanding of the problem, a way to detect/diagnose it, and a solution (with GRJ and others thinking about taking the work done so far and making it better). Everyone has access to this detailed write up and history of the thoughts so far. What could be better?
You have done an excellent job with this bit of problem identification and solving, Adrian! It's all way above my head, but I have truly enjoyed reading this thread and learning about how you approached both the problem and the solution. Very nice work!
I'm with Allan. Although not totally over my head I do enjoy seeing others make the hobby better!
Adrian! posted:.........Some members have brought Rev L TIUs from home recently bought and installed and I've found the same TVS failing also.
1. Well, GGG, he also wrote the above. You don't suppose those members let children play on those home layouts, do you ?
2. If prolonged shorts are the 244 killer, wouldn't the best "control" test be Rev L boards with no [ 244 ] TVS protection BUT the newly purchased front end units [ PSX-AC ] that GRJ recommended ? I don't he tried that combination.
SZ
Steinzeit posted:Adrian! posted:.........Some members have brought Rev L TIUs from home recently bought and installed and I've found the same TVS failing also.
1. Well, GGG, he also wrote the above. You don't suppose those members let children play on those home layouts, do you ?
2. If prolonged shorts are the 244 killer, wouldn't the best "control" test be Rev L boards with no [ 244 ] TVS protection BUT the newly purchased front end units [ PSX-AC ] that GRJ recommended ? I don't he tried that combination.
SZ
Hey there!
If you read back from the start we mentioned the setup with the TVS failures had PSX-ACs installed on each and every channel. They're digital on a 20MHz clock so they aren't really that fast (50ns ish). The TVS themselves clamp on the order of 1ns depending on lead inductance.
Adrian! posted:Steinzeit posted:If you read back from the start we mentioned the setup with the TVS failures had PSX-ACs installed on each and every channel.
Well, I had read this thread from the start. As I understand it, you installed the PSX units on Nov 16th at the same time as a new group of ex-factory Rev L 's were installed. But you've never operated any channel as I've described as I understand your posts; that is, PSX + non-TVS L's -- have you ?
SZ
GGG posted:If you build this board build in a LED light that illuminates when the TVS Shorts.
Easier said than done. Without some extra components, I don't see any way to do this. Extra components means more expense for each board as well as a larger board that may not fit on top of every ACT244 in all the TIU versions.
Adrian, did you see my suggestion to simply use a 3000W TVS and eliminate the diodes? I wonder if that would be robust to make this a "one component" solution? After all, there can't be that much energy constantly bombarding the 244's, or they'd be failing all over the world. As George points out, while we do see them failing, it's not a avalanche of them as a rule. I'm just wondering if the part was robust enough, it would absorb whatever punishment was being dished out by the signal transformer kicking back to the 244's.
Adrian! posted:gunrunnerjohn posted:I'm just wondering if there isn't a much simpler solution here. As far as the TVS, how about forgetting the silicon diodes and just putting one of the big honkin' 3kw TVS diodes right across the gates and dispense with the diodes. It'll take a much bigger beating than the 500W ones that you were testing with, and with the adapter board, it should be easy to piggyback on the existing ACT244. I'm thinking of something like this Littlefuse SMDJ7.0CA. Hard to believe it couldn't stand up to a fair amount of punishment. It's small enough to perch right on top of the ACT244 on a little PCB.
Uh some details. The scope is looking at the output side of the transformer, not the waveform right at the clamping device/ACT244 driver output pins. Clamping from 0 to 7 volts could work but again it's got to be quick quick quick. A small zener or TVS is faster than a big zener since Cj is the dominant term in the time constant which grows with anode area.
Maybe a small TVS in parallel with a big TVS?
I missed this in all the responses. That's not a bad idea, I think I'd make the small TVS just a bit higher in voltage so that when the big one did clamp, it takes the stress off the smaller one. What do you think, a 500W one like you used and the 3000W one?
Any chance you could equip one of your TIU's with this combo since you have the ideal testbed? Or, maybe we can get Bob at NJ-HR to try this fix. If we can come up with a working fix that only has a couple of components, it would be easy to make the piggy-back board that could be plopped on top of the 244's.
I checked the 3000W one I specified, it has a pretty decent response time, and the added capacitance of the little board should be minimal if we do it right.
Fast response time: typically less than 1.0ps from 0V to BV min
