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My layout in split electrically into 2 blocks that are isolated by a single insulated center rail joiner. Each block is powered by its own Lionel 180 watt powerhouse that runs through each of the 2 fixed voltage channels in my TIU. I have discovered that both the powerhouse for fixed voltage channel 2 and the fixed voltage channel 2 itself in my TIU are not operating. The isolated powerhouse for channel 2 produces no voltage on my volt meter. The input and output TIU connections for channel 2 both read zero on my meter when powered by either the seemingly failed powerhouse or a postwar set transformer. I have determined that the fuses in my TIU are fine by swapping the 2 fixed voltage channel fuses with channel one working and channel two dead, regardless of which fuse is in which slot. The only other strange symptom is that my volt meter shows 18 volts when I test the voltage between the center rail of the dead block and the live block - I did this test after an engine caused lots of sparks after it was inadvertently routed from the live block into the dead one! And no, I can’t find a short circuit in block 2.

I know that my powerhouse for channel 2 probably needs to be replaced under warranty - it’s just 1 month old. But does anyone have any idea what’s up with my TIU fixed voltage channel 2? I’m concerned that a failure with channel 2 in my TIU may have trashed my powerhouse... and could well trash a new replacement powerhouse!

Thank you for your thoughts!

Peter

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@Peter C posted:

...The isolated powerhouse for channel 2 produces no voltage on my volt meter. The input and output TIU connections for channel 2 both read zero on my meter when powered by either the seemingly failed powerhouse or a postwar set transformer.

What does meter show for continuity/Ohms between red and black Fixed In 2 jacks?  Does it indicate a short circuit?  If so perhaps your TVS protection diode inside the TIU failed (is shorted).

In which case, not sure why the Powerhouse did not protect itself and is now dead...but if your PW transformer reads normal voltage by itself but 0 Volts when attached to Fixed In 2...then it seems to me TIU Fixed 2 is internally shorted.

For a simple bench verification of a shorted-TVS you can simply clip one terminal of the corresponding TVS diode and see if the short goes away.  There have been dozens of OGR threads on managing/replacing the 50-cent TVS diodes.

MTH might have changed the placement of the TVS diodes between revisions but here's what it "might" look like...

TIU fuse and tvs

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  • TIU fuse and tvs
Last edited by stan2004

Not familiar with the OGR meter.

But unless it's some odd-ball design, do the following.  Place it in the Ohms/Continuity mode.  It doesn't matter the range...but if there is a choice use the lowest range.

Note the reading with the meter probes not touching each other.  If a numerical reading is indicated it should be some ginormous number in the millions or billions ... but more likely maybe just some dash symbols showing it's a huge number.

Then touch the two probes together simulating a short-circuit.  The numerical reading should go to zero (0) or something near zero (i.e., less than 1 or 2 Ohms).

Then put red probe on the red Fixed 2 input, black probe on black Fixed 2 input.  What does it read?  I'm betting it's some very small number indicating a short circuit.

Oh.  This is with NOTHING connected to the output of Fixed 2.

Last edited by stan2004

So when you connect your postwar transformer to fixed in 2 on the tiu, with nothing connected to the fixed 2 out, your meter reads 0 volts on both input and output of tiu fixed 2?

@stan2004 posted:

What does meter show for continuity/Ohms between red and black Fixed In 2 jacks?  Does it indicate a short circuit?  If so perhaps your TVS protection diode inside the TIU failed (is shorted).

In which case, not sure why the Powerhouse did not protect itself and is now dead...but if your PW transformer reads normal voltage by itself but 0 Volts when attached to Fixed In 2...then it seems to me TIU Fixed 2 is internally shorted.

This seems like the case... but if the TVS is a dead short, then I’d think the breaker/fuse in the postwar transformer would have popped, and or a shower of sparks and some magic smoke.  

@rplst8 posted:

So when you connect your postwar transformer to fixed in 2 on the tiu, with nothing connected to the fixed 2 out, your meter reads 0 volts on both input and output of tiu fixed 2?

This seems like the case... but if the TVS is a dead short, then I’d think the breaker/fuse in the postwar transformer would have popped, and or a shower of sparks and some magic smoke.  

Yes, meter reads 0 volts on both input and output of TIU fixed 2. And yes, my little postwar transformer became warm very quickly and started to smell hot... I immediately unplugged my transformer at this point! I’m not sure about the breaker/fuse protection in my postwar transformer since it is a very small cheap unit that came with my first 027 set in 1962.

Are you saying between the center rail of the dead, and the outside rail of the live one?

Not the center to center of the 2, right?

So power is getting thru somewhere.

Yes, I am saying between the center rail of the dead and the center rail of the live!

I’m thinking that my meter reading of 18 volts in this scenario means that my TIU fixed 2 output must be shorted out, perhaps by a failed/shorted TVS as other forum members have suggested.

@Peter C posted:

Yes, meter reads 0 volts on both input and output of TIU fixed 2. And yes, my little postwar transformer became warm very quickly and started to smell hot... I immediately unplugged my transformer at this point! I’m not sure about the breaker/fuse protection in my postwar transformer since it is a very small cheap unit that came with my first 027 set in 1962.

Ok, then I’m with the others... likely a shorted TVS.

@stan2004 posted:

Not familiar with the OGR meter.

But unless it's some odd-ball design, do the following.  Place it in the Ohms/Continuity mode.  It doesn't matter the range...but if there is a choice use the lowest range.

Note the reading with the meter probes not touching each other.  If a numerical reading is indicated it should be some ginormous number in the millions or billions ... but more likely maybe just some dash symbols showing it's a huge number.

Then touch the two probes together simulating a short-circuit.  The numerical reading should go to zero (0) or something near zero (i.e., less than 1 or 2 Ohms).

Then put red probe on the red Fixed 2 input, black probe on black Fixed 2 input.  What does it read?  I'm betting it's some very small number indicating a short circuit.

Oh.  This is with NOTHING connected to the output of Fixed 2.

Thanks @stan2004 for coaching me with testing continuity! With a randomly selected Ohms/Continuity range, the meter reads 1. when not connected to anything and .000 when the probes are touched to each other or to the fixed input 2 connections.

Do these readings indicate a short inside my TIU, possibly from a failed TVS? And could a defective Lionel 180 watt powerhouse cause the failure of the TVS inside my TIU?

@Peter C posted:

Thanks @stan2004 for coaching me with testing continuity! With a randomly selected Ohms/Continuity range, the meter reads 1. when not connected to anything and .000 when the probes are touched to each other or to the fixed input 2 connections.

Do these readings indicate a short inside my TIU, possibly from a failed TVS? And could a defective Lionel 180 watt powerhouse cause the failure of the TVS inside my TIU?

Those readings indicate a short.  

If the breaker did not trip correctly, the PowerHouse most certainly could have supplied too much current for too long and cooked something inside the TIU.  

That said, in a case like this it’s pretty hard to determine what was at fault over the Internet.

I can’t think of a scenario where a TIU could “kill” a modern transformer though.

@Peter C posted:

Thanks @stan2004 for coaching me with testing continuity! With a randomly selected Ohms/Continuity range, the meter reads 1. when not connected to anything and .000 when the probes are touched to each other or to the fixed input 2 connections.

Do these readings indicate a short inside my TIU, possibly from a failed TVS? And could a defective Lionel 180 watt powerhouse cause the failure of the TVS inside my TIU?

Yes. It appears there's a short inside the TIU on Fixed 2.  Since this all happened following a power mishap on the track, a failed TVS is a good suspect to follow.  That is, sparks/fireworks are notorious generators of large voltage spikes.  And the TVS is a protection device that is meant to block the sensitive TIU electronic components from "seeing" those large voltage spikes.

So in what I think is the likely scenario, the TVS did its job and gave its life doing so.  Sounds overly melodramatic but it is what it is.  And assuming it is in fact the TVS that failed, I don't think it was anything about the PowerHouse that caused the TVS to fail.

If the PH is under warranty then I would leave it at that.

As mentioned earlier, replacing a TVS can be a DIY project but it does require soldering.

If you want to investigate a bit further to see if you want to jump in the deep end, it is fairly straightforward to lift off the cover of the TIU by removing screws from the bottom.  That will show something like previous photo.  Do a visual inspection looking for anything egregious like blackened or charred components and the like especially in the area between the Fixed 2 input and output jacks.

Then find the 4 TVS diodes using the earlier photo as a guide (as mentioned there have been revisions to the TIU so perhaps they've moved a bit between revisions).  Even if you choose not to replace the TVS itself...and you're going to have someone else do it...I'd simply want to know and would use a diagonal cutter to clip one terminal lead of the TVS as illustrated below.  Then re-measure the continuity between the Fixed 2 power input jacks.  Did the short vanish?

TIU TVS

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  • TIU TVS
Last edited by stan2004

I find it VERY difficult to believe that a short, or pretty much anything you do at the output of the Lionel Powerhouse 180, killed the transformer.  I've been using the Lionel PH180 transformers for many years, and I've never killed one with the thousands of short circuits, cross connections, etc.  I've seen a failure of the circuit protection in one PH180 in our modular train club layout, but it was a random component failure, not the result of any abuse.

....

I've seen a failure of the circuit protection in one PH180 in our modular train club layout, but it was a random component failure, not the result of any abuse.

So the TVS failed shorted, and (possibly) took out the PH180?

Could the PH180 have taken out the TVS somehow?

This seems interesting to me. The PH180s seem to trip so fast, and for lighter reasons than anything else I have. I have inline fuses on my circuits and the breakers on the PH180 will trip first. The Z4000 for example, will keep supplying power on the same circuit for longer periods, depending on the short?

I mainly run 2 rail and haven't lost an internal TVS yet, after maybe 15 + years. I have changed out plenty of external 10 amp auto fuses using different power supplies. So I use them even on the PH180 circuits.

Last edited by Engineer-Joe

My 180 watt powerhouse is brand new... I hadn’t run any trains yet on that block until I discovered the problem. I don’t think the sparks from my engine crossing into that block caused the failure, but rather alerted me to a failure that was already present. My new powerhouse may have been defective right out of the box. If so, could a defective powerhouse burn out the TVS inside my TIU?

Thanks to everyone for your help with this problem!!!

@Peter C posted:

My 180 watt powerhouse is brand new... I hadn’t run any trains yet on that block until I discovered the problem.

You do realize that the new Powerhouse 180 requires a 3rd pin in the connector to enable power, right?  Are you sure you just aren't missing a simple interlock?



You guys will work this out for him. That, I am sure of.

Last edited by Engineer-Joe

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