I discussed this on another thread and have the same issue on a second Rev L TIU. When engines cross onto the blocks controlled by a Variable 1 channel set to fixed they slow to a crawl. Input voltage is 20 volts on the Var 1 channel and the output voltage is 12 volts under load. When I disconnect the output and measure the voltage at the output of the TIU its 50 volts. It is not my meter Tried five different meters in increased quality. This is the second TIU that has had the exact symptom Anybody here any issues with the Rev L?
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Sounds odd alright, I would look at it with an O-scope.
I wish I would have kept one of them I had two when we were throwing them out at IBM Said what the heck can I do with these and threw them out about two years later
Attachments
I'm guessing you read this thread
https://ogrforum.com/d...nt/11285375692904415
I know you're a very experienced DCS operator ,what do you think is going on,, hardware or software.
Its definitely Hardware That other thread is something completely different. Both of these rev L's failed the same way Heard of two other people with the same thing
I don't want to sound stupid, but have you tried swapping channels of the TIU to see if the problem follows the channel, or is related to the load the block/section of the layout presents to it?
Ben,
It's probably time to call MTH service.
Called MTH They say its coincidence that its Var 1 They say the meter is reading across two waves and it really isn't 48 volts Problem is the FET component There are 4 per channel Will try to replace these and see what happens Usually caused by spikes as in a bad derailment
Thanks for the update Ben I was curious as to the cause.
It is possible only one blew, but you have to take them all out to figure out which one it is. G
Ben, Please post the part numbers of the FETs. Might be a good idea to stock up on few. Does MTH offer schematics for the TIUs? I'm curious why the TVS's didn't protect them.
Pete
Ben, our experience with TIU failures at the Boston Metro High railers is similar... Most of the failures (whether Rev L TIUs or other models) have been Power FET failures... The TIUs that have failed that were still in warranty we sent back to MTH for repair... Those that were out of warranty we repaired ourselves... Our chief engineer has gotten very adept at replacing the power FET transistors... I think it's true (at least anecdotally) that the replacement power transistors have not failed after installation... Somewhere I have the transistor types we have used... As soon as I find them I will let you know... Also I will talk to our Chief engineer and see what additional information he can give me...
The last TIU failure we had concerned loss of DCS signal; that went back to MTH for repair (replacement of the DCS signal generator chip)...
The fans we have installed on our TIUs at the club have also helped to reduce (but not eliminate) TIU failures at the club...
I look forward to the FET numbers myself, I'll probably stock a few in advance.
gunrunnerjohn,
it might be a couple of days before I have the info from our Chief Engineer... But I have the data sheets at home which I will pass along to you after I crsss check with the Chief!! If I remember correctly we got the info from reading the writing on the transistors themselves... Also, if I remember correctly, they are some kind of IGFET...
No hurry, my TIU's are working fine right now. I do know a guy that asked me about a channel on his, so I may have a use for them.
Haven't been able to locate the MTH part numbers in all my documentation. They do not have any PN listing for TIU's on the website either Jim I will appreciate the numbers too! Plan on stocking these as it seems the Rev L has more issues with them than the previous models we used. We installed the fans on these guys as per your pics too Jim We haven't had any meltdowns as we did previously. They help alot.
Ben, where can I find the information on the fan mod you guys have done?
Dave
I saw some pics that Jim Queenan from the Boston Metro Hi-Railers club posted One of them had their TIU's showing a squirrel fan from a personal computer mounted above the TIU in a special cradle hence cooling it down while operating. Large DCS installs pull alot of power through the TIU's and it caused meltdowns when all lines were operational. I didn't use such a high tech installation. I didn't use any kind of cradle I just took a 4 inch squirrel fan and taped it to the top of the TIU.
Just sticking the van on top is probably plenty, that will provide significant cooling over natural convection.
While you have the TIU open, it's a good idea to check the terminal nuts on the inputs and outputs. Some I have checked were loose and it can cause problems with the signal and possibly melt the plastic around the posts.
Good idea Joe, I found most of them loose when I opened one of mine. Come to think of it, I probably should open the other and make sure they're tight as well!
Wonderful to hear of these issues. I just ordered a new TIU and am not too likely to be able to fix it myself. Maybe the new batch won't have these problems.
Ed
Are we supposed to put a cooling fan someplace where it can blow air over the TIU? I've got a new REV L coming and would like to avoid problems. Does anyone recommend any other precautions?
Ed
You can just plop a muffin fan on top blowing into the TIU, it's the easiest way to get forced air into the unit.
Is a muffin fan just a little fan? Where do you get them (I assume not a bakery!)? Is it supposed to blow into the unit?
Ed
Muffin is a brand name that has been assigned to the type like Xerox for copying. There are many manufacturers today. If you have a desktop computer there are likely 2 or three inside or attached to the case or power supply. The vary in size from under 1" to 4" and larger square. I suspect they might be found at Radio Shack or if you have an old unused computer you could take one from it. The computer models run on 12 V DC but larger ones operate on 120 or 220 V AC. Google muffin fan and you will see what they look like.
Pete
While you also have it open check to see what the value of the TVS, if you can get to them, is. If they are not rated for spikes above 35 volts you might consider installing additional TVS's in the inputs and outputs of the TIU.