TIU Help - short circuit

What rev TIU is it?  You most probably blew a fuse or diode on Fixed 1 input.  Yes - this can be fixed.

bruce

Rev L is pasted on the bottom of the unit.  The fuse on the Fixed 1 input definitely blows as soon as power is applied 

Check the diode on the output for that channel.  If there is continuity across the leads, it must be replaced.

Won't be a fuse that causes short.  As Dave says, most likely the TVS diode failed shorted.  This is repairable.  G

Check the TVS diodes, if you find a short across any one of them, that's your problem.  I the shot below, it's the large black device next to the multi-color coil.  The one for fixed #1 will be pretty close to the output connection for fixed #1.

D300 is the one you're looking for.

All,

Thanks much for the responses.  GRJ the picture and diagram especially helpful - thanks for taking the time to post those.  I'm traveling this week, but back on Friday and I will check it out.  Couple of more questions since I am definitely not an electronics expert:

How do I check for a short across the diode?  I do have a multi-tester if that will help.  If I do have short in that diode, where can I get a replacement?  I imagine it is something I will have to order, but from an electronics store or MTH?  

In the meantime, can I set up the TIU to run my trains via the fixed 2 input/output?  If so, how do I do that?

Thanks again

Just check for continuity across the leads.  You can get the part from DigiKey or Mouser etc.

This is what I use when I replace those: 1500W 36V TVS at Digikey

Where can i get the diode for the tiu if i need it mth?

@santa fe posted:

Where can i get the diode for the tiu if i need it mth?

Did you see this?

That link is the TVS diode in question.

Having the same issue with my TIU that @Scott R had. I am electrically challenged so was hoping for some help in answering these questions.

1. I have a Z-500, do I plug that into aux power input before checking for continuity across the leads of the D300 diode?

2. Do I check continuity using DC or AC on the meter?

3. I purchased the TVS diodes from Digikey, one side of the lead has red tape on it and the other white. Can I cut the leads down to fit into the TIU?

4. Are each of the leads on the TVS Diode the same? does it matter which direction I solder it to the TIU? Not sure if one is hot and one dead???

Thanks for your help

You can check the four TVS diodes in circuit with a standard ohmmeter.  Just measure across them, any bad one will usually read a direct short.  If it's just a TVS diode, I clip the leads next to the body, heat the solder joint while holding the lead in forceps, and pull it out.  You can then solder the new one in from the top without undoing a sea of binding post nuts.

The TVS diodes are bi-polar, that means they don't have polarity.

Thank you for the information and how to on the TVS diode @gunrunnerjohn. I was able to remove the old one and install the new one and it worked!! The Z-500 is no longer blowing its breaker. 

Love those success stories.