Hi Everyone - First post here. I'm trying to help out a neighbor whose husband just passed away, and I'm new to the MTH DCS, but not new to electronics. The rev L TIU is blowing fuses on fixed output 1 and 2 immediately on power-up, with nothing connected to the output terminals at all. There's a power brick connected to fixed input 1 and 2, and also to the Aux power in. Can you suggest what might be wrong here?
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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!
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!