TIU Rev. L Variable 2 failure

https://ogrforum.ogaugerr.com/...3#159660139297244143

@Vernon Barry posted:

Add one more,

Variable channels with constant ON track power output, most likely a bad TVS which has shorted out (1.5KE51). These are in parallel to the MOSFETS so when they short, even if the MOSFET is off, you get the full voltage out bypassing the control by the MOSFETS.

FWIW- Zcontrollers have the same (1.5KE51) in the same arrangement in parallel to the variable control MOSFETS and have the same result- constant output regardless of handle position when that TVS fails shorted. Picture and details here https://ogrforum.ogaugerr.com/...4#154167236021571964

My method is to use a side cutter to clip one end of the TVS diode leg and then check with a meter when you have one suspected shorted. This removes it from the circuit but still allows you to test the device with a meter. Again, the problem is, we have more than one device in parallel that might have failed- so disconnecting the cheapest and easiest one to replace (2 leg diode VS 3 leg MOSFET).

In addition, there are also 4 TVS diodes by the outputs.

https://ogrforum.ogaugerr.com/...31#81537088535745431

And https://ogrforum.ogaugerr.com/...8#154730473580243678

@stan2004 posted:

What does meter show for continuity/Ohms between red and black Fixed In 2 jacks?  Does it indicate a short circuit?  If so perhaps your TVS protection diode inside the TIU failed (is shorted).

In which case, not sure why the Powerhouse did not protect itself and is now dead...but if your PW transformer reads normal voltage by itself but 0 Volts when attached to Fixed In 2...then it seems to me TIU Fixed 2 is internally shorted.

For a simple bench verification of a shorted-TVS you can simply clip one terminal of the corresponding TVS diode and see if the short goes away.  There have been dozens of OGR threads on managing/replacing the 50-cent TVS diodes.

MTH might have changed the placement of the TVS diodes between revisions but here's what it "might" look like...

All that to say yes, a TVS that failed would get very hot. Between the diagrams you can validate but definitely sounds like the normal failure.

It is a revision L but in the second picture posted it is the TVS at the top far right. Is this something I can get from Mouser or Digikey?

@Markw posted:

It is a revision L but in the second picture posted it is the TVS at the top far right. Is this something I can get from Mouser or Digikey?

Factory that TVS is a 33, the ones by the heatsinks are 51s.

1.5KE33CA

1.5KE51CA

https://www.digikey.com/en/pro...sBpAogZgwYQIIgF0BfIA

Also, not saying this is the cheapest, but MTH parts also carries them - and other parts for the TIU.

Search for "TIU" https://www.mthpartsandsales.com/shop/search/results

Yes   It's a 1.5KE39CA/1

Mouser

DigiKey

I see Barry and I were looking it up at the same time....

Hi you know a quick way to test and make sure tiu worked is just cut out TVS diode and power up and test, 10 - 1 it will work, then all you have to do is order TVS diodes and replace then retest!

Alan

That's exactly what I did this morning. put my meter on var 2 output and channel acted in a normal manner. I ordered the diodes yesterday and will recieve in 2 days. Thanks everyone for their help on this matter.

@Vernon Barry posted:

All that to say yes, a TVS that failed would get very hot. Between the diagrams you can validate but definitely sounds like the normal failure.

What list of issues cause TVS failures Vernon ? 

I have the Rev L fully updated.   I've run it for a half dozen years with 2  Z1000s on fixed 1 and 2 on two seperate loops.

I have noticed the side near the red indicator light getting fairly warm through the vents when running engines with a combined 8 motors or more on the two loops.

Since I know the jumbo Lionel and MTH transformers and our little Lionel Power Max 40w all have cooling fans I figured the TIU  , not really a transformer but a controller of sorts , would benefit from some sort of fan.