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I have four circuits passing through a TIU.  Recently, the circuit passing through position 4 stopped working.  As I apply power to this circuit, the Z-4000 shows amps increasing to about 8 as the voltage reaches 12.  And, the track that is serviced by this circuit shows no power.  So, I moved the input/output of position 4 to position 3 on the TIU and the circuit worked fine.

I would appreciate suggestions on what I should try to fix the problem.  Perhaps I should send the TIU in for repair or just buy a new one.

Thanks,

Tom Jasper

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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.

MTH TIU TVS Diode Locations

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  • MTH TIU TVS Diode Locations

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

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