TIU Problem

This is the classic sign of a shorted TVS diode, a fairly easy fix.  You can actually do this repair without taking the board out.

John, that's encouraging.  Can you refer me to a reference that describes how to fix a shorted TVS diode?  And, are parts required?  

I probably caused the short when I commanded a N&W J to move forward, but a PRR Q2 that somehow had the same address moved from a siding and plowed into a passenger train shorting out the track circuit that has the problem

Thanks,

Tom

Measure these four components, when you find one with a short, that's a shorted TVS diode.  What I do is clip the leads at the failed part, then individually pull them out by heating the wire, and finally clean out the hole and solder a new one in.  You should be able to do that without removing the board and the sixteen terminals.

@Tom Jasper posted:

...And, are parts required?  

See this post in the Electrical Reference about buying the TVS replacement part itself. 

It's one of those you'll pay more for shipping than the part itself.

@stan2004 posted:

It's one of those you'll pay more for shipping than the part itself.

That's why I like to try and stage my orders until I have $30-40 worth at least and then fire them off.

Thanks John & Stan.  I'm leaning towards buying a new TIU and then attempting to repair the damaged one so I don't have an interruption of rail service.  Tom

You could just leave the 2 tracks fed off one channel, until you gather the parts

I may do just that John as it appears that no dealer has an TIU in inventory.  Thanks, Tom

First off, see if you can find which TVS has shorted.  If you identify one shorted, remove it and see if the channel is functional again.  If so, I can put one in an envelope and send it to you.

Thanks John for your great offer.  I have an older pre-Rev L TIU that I believe has the same problem.  So my plan is to service two track circuits with one TIU feed from my Rev L TIU, and have a look at the four TVSs in the older TIU to see if one of them is bad.  This way I can continue to run trains as I bootstrap my way back to a fully functioning TIU.  Thanks for your insight and offer to mail a needed part. Tom

As a temporary fix you can simply clip the leads and remove the failed internal tvs. Then fit a new one to the tiu output posts using the handy holes in the output banana plug posts. Standard tvs PN's for train use have been posted many times on the forum. If you have any on hand you are set.

Rod