TIU Blows fuses with no load

check across  the output fixed 1  n 2 with a ohm meter more then likely you'll se a dead short and usually caused by TVS diodes arcos all four channels. check across each channel red n black terminal, you will find at least one or 2 of the red and black outputs shorted! you can cut one end of the diode ounce you find the short. with one end disconnected  actually go across the diode by itself see the short then l while disconnected. if you loose the short when shorted didoes is removed. then what you'll need to replace to put the tiu back in working order! the diodes are used for voltage spike protection from derailments and accidents!

Alan

You can measure them in circuit for shorts, but Alan is almost surely correct, they're shorted.

Measure each of the four TVS diodes, if you find any that read a direct short, they need to be replaced.

It's possible to do this job from the top, but it takes a bit of finesse with the soldering iron.

Here are the locations of the parts in question.  Click on graphic for full-sized version.

Sure enough, two of the diodes are showing 0 ohms.  I'll have to find some replacements.  Thank you both!

1500W 33.3V TVS at Digikey

Thanks for the part numbers

Can you just cut out the TVS and not replace it?  Then put a TVS between the TIU and the track?

Since the TVS devices are on the output side you can put them on the outside although this is not very convenient for the other wires.  I routinely do this to test the circuits with trains once I have made the initial cut in the offending circuit.  I do replace them however since I find internal protection a lot less clumsy than external.  As John said the job can be done from the top you just have to use a low wattage iron and be really careful not to overheat the board.

Rolland