TIU Rev L problem

 This thread is very similar...

https://ogrforum.com/t...29#70974704706010529

There are a number of excellent repair guys  on the dcs forum... One will probably show up shortly.

I believe forum member GGG repairs TIUs. He is recommended here a lot by other users.

I do recommend GGG for TIU repairs.

My E-mail is in profile. G

I just looked at a TIU yesterday that had the same problems.  Other than checking the diode, what might be the problem here?

Thanks,

Dave

The driver FETs are the most common issue for loss of output on the variable channel.

John,

Would you test them with the ohm setting?  What should a normal value be?

Thank you for the reply.

Dave

You can test them with a meter, but normally you have to remove them to get a valid test.  Given the fairly low price of the FET, if I'm going to pull them, I just put new ones in. I figure doing repeated remove and replace operations on the PCB are more expensive than just replacing a few inexpensive parts.  If you buy 10 or more, they're only $1.38/ea.

IRFZ44PBF at Digikey

Testing a MOSFET

Thank you for the replies, GGG I will email you later today. And Dave this past nov. my boys and I stopped in for the first time and purchased an MTH trolley from you, anyways was wondering since I live close to you, are you an autherized lionel service center??

thanx Jim 

John,

Thanks!

Dave

I have a TIU with the input on Fixed 1 is out.  I have to power the TIU with the Aux power on a walwart..  The other channels remain fine.  IS this the same repair for that? 

No, fixed channels don't have FET's.  Did you check the obvious, the 20A fuse?  If power doesn't make it through from the input to the output, and the fuse is good, that's not a good sign!

GRJ, if not the fuse, could it be the TVS in Chris D's problem on the fixed channel?

Well, if the TVS is shorted, it would blow the fuse.  If the TVS is open, it would have no observable effect.  That's one reason I asked about the fuse.

It's important to know the EXACT symptoms of any failure to be able to zero in on a possible failure. 

Does the channel output power if you have power in the input?

Thanks, so with an open TVS the TIU channel would still work as in normal operation. I wasn't sure how what the open TVS would do, so that is good to know. Makes sense that it would blow the fuse if shorted, but I can't say that I knew that either, so two things learned here. 

An open TVS is undetectable, and the TIU would operate normally, just without the spike protection that was provided by the TVS.

That would be good reason to have those few extra TVS' (or TVS's?) scattered around the layout. Good enough for me anyway. As a good friend of mine always tells me, 'anything worth doing is worth overdoing'.

gunrunnerjohn posted:

An open TVS is undetectable, and the TIU would operate normally, just without the spike protection that was provided by the TVS.

I installed the TVS on each TIU channel; how can I tell if they have failed?

If they short, the breaker/fuse trips.  If they are open, you can't tell without a sophisticated test.  If you have doubts, just replace them periodically.