Rev I tiu voltage issue.

I believe minimum voltage is 5.5 on variable channels unless you have manually set them to 0.  

If you've punched the TZV hotkey on the remote and that track doesn't go to zero, it's likely an issue with the TIU.

Minimum track voltage setting is 5V unless you've configured a different voltage.  Also, the voltages displayed are based on 22 volts going in, if the input voltage is less, then the voltage indications will be higher than actual voltages.

This sounds a lot like blown variable channel FETs.  I blew the FETs on both of my variable channels due to derailments.  I replaced the FETs on one channel and it works fine.  I will eventually get to the other one.  I am not sure which TIU revisions are prone to this problem.  The symptom I had was voltage passing through at a constant level.  The red button on the remote did not shut off the power to the channels with the blown FETs.  There are a number of posts on the FET problem.

I didn't try the red button at the time, just pulled the power from the source going into that channel.  I was operating for my kids and just wanted something quick.  As I stated I scrolled the output channel voltage to zero with no effect.  Never had that problem before.  

Is this fet a plug and play style part or does it get soldered in?  ( And yes I will look up the other threads when I get some time.)

The FET's are most certainly not PnP!  You have to remove the PCB, (think 16 nuts holding the posts), desolder the FETs, and then replace them.

@gunrunnerjohn posted:

The FET's are most certainly not PnP!  You have to remove the PCB, (think 16 nuts holding the posts), desolder the FETs, and then replace them.

Worth while to repair or better to replace?

Certainly cheaper to repair that replace, if that's the question.

@gunrunnerjohn posted:

Certainly cheaper to repair that replace, if that's the question.

Yup, that was the question.   Now I just have to find someone doing repairs.   I don't think mth is taking anything in for repair right now. 

Not likely!

Mike Wolf to retire and close MTH

Yea, I just saw that.   

Dear God, 2020 sucks enough already.  Please consider easing up. 

Ok, so my tiu gave up channel 1, I suspect since was using a 21v Z-750. No short or derailment, just stopped working. Probably not a good idea, since I have a couple of z1000s rated at 18v. Channel 2 works with the z1000. Question is, should all the tvs in the tiu be replaced ?

DCS voltage readings are based on 22 volts, as John said above, so I don't think your Z750 is the cause of your problem.

Well, certainly all the TVS parts don't need to be replaced.  If the TIU isn't shorting out the transformer input, you don't have a TVS issue anyway.

How about starting with the exact symptoms and the hardware rev of the TIU?

Hi John, It's Rev L.

The Z750 kicked the circuit breaker on fixed 1. No derailments,  just the breaker. Disconnected track, still same. Tried another Z750,  same result.  Tried Z1000 same result. No smoke, no warning from TIU. Train was moving about 25 smph and just stopped.

I setup the Z1000 on Fixed 2, jumpered the aux port from it and it works with a different egine. I haven't put the original engine back on the track, but I'll check that one without the TIU, and just try it in conventional first.

I'll can email you If you be so kind to repair it for me.

Thanks,

OK, that's most likely the TVS, you just have to replace the one associated with channel #1.  Easy to find, just measure them with your meter, and the one that's shorted is the one that's bad.  If you are decent with a soldering iron, you can do this one without taking the board out.  That's a bit of a PITA with the sixteen posts to loosen and then put back in.

Clip the old part right next to the body leaving a chunk of the lead sticking off the board.  I grip the end of the lead with medical forceps and heat the joint on the board and lift the old lead away.  You may have to put a small blob of solder on the joint first to get heat to it, I set my iron at 650F for this job as there's some large traces to those pins.  Clean the holes out, (I use my solder sucker) and solder the new part in.  I use the 1500W 33.3V TVS at Digikey for the replacement.

And the way to fix it without soldering:
Open the TIU and clip the defective TVS out on both sides, put the TIU back together and add TVS protection externally to the TIU on the output terminals.

I've seen someone do this, it works but it's not how I would fix it!  John's way is the best and will ensure nobody would ever remove your external TVS protection by accident.

Interesting fix, and it would indeed work.

Interesting indeed... humm, ok.

I'm thinking to put an external TVS on all 4 outputs. I currently only use 1 channel, but will be expanding my layout next year.  So, IF a problem comes up on the other 3, would the external ones go first or the internals?