MTH DCS TIU TVS shorted?

https://www.digikey.com/en/pro...inc/1-5KE33CA/688026

MTH parts and sales https://www.mthpartsandsales.com/shop/search/results

Thank you!

I found an old save of a similar piece and I don't remember what it went to

1.5KE39CA Littelfuse Inc. | Circuit Protection | DigiKey

the original has 33 printed on it, not 39

Also another with 36

TP1.5KE36CA Littelfuse Inc. | Circuit Protection | DigiKey

The 2 digit number is (Edit- read the data sheet- but a "correlation" to) the voltage rating of the device.

Stock it came with 33 and your other channels are currently protected to "33".

Higher numbers equate to higher voltage values when looking at the sheet. Example, 36 is higher, and 39 is even higher. This is the voltage they let pass into the REST of the expensive electronics in your TIU.

Again, a simple concept. This device protects and attempts to block higher than "normal" voltage entering the TIU. You want a value that doesn't short normal operation, but also provides some minor headroom, but not so much headroom damaging spikes come in and pass through. MTH factory chose 33- you can use other values- higher is less protection in this perspective.

Note that the 1500W 33.3V TVS at Digikey actually has a breakdown minimum of 34V.  Since the TIU is rated at 24VAC input, that doesn't leave much headroom from the 1.414 peak voltage of 24V RMS, that's 33.936 volts peak.  The 33V rated TVS would have min breakdown of 31.4V, well below the peak possible with normal voltage inputs.

Thank you both for the info.

Now, to pick one.

I tend to go with what's original.

In one of my power amps from Crown, it was posted that the original start up cap, could be blown from regular use. The specs didn't match what was actually occurring. A recommended change was posted. I went with that because it sounded correct.

Now, I can't decide on this. I have four TIUs that have run for years without issue. So was this some specific occurrence?

the clamping voltage seems to be important? I really don't know which is most? I know just enough to get in trouble here.

What do you use for input power to the TIU?  If it's 18V, the lower clamping value TVS should be fine.  Truthfully, the difference in actual protection is minimal between all the choices being discussed.   The truly damaging spikes are well above the clamping threshold of any of the possibilities.  Voltage transients are routinely recorded at up to several thousand volts, they only last picoseconds, but that's enough.

On this TIU it's a Z4000 from MTH. I had the handle set at around 22 volts.

On my 2 rail, it's (usually) Lionel 180PH bricks. I use a handle of the Z4000 when I run my MTH Big Boy.

Outside, It's Bridgewerks DC power that I set at around 24v for G scale.

Again, this is the first issue of this, in over a decade of use.