TIU VARIABLE CHANNEL NOT WORKING

Hi folks

 

 My TIU  variable channel #2 is not working . It seems that is due to a damaged output FET. So, it was only possible to see the code of the first TR, which is IRFZ44N. My question is: are all 4 TR's of the same type?

Thanks for reply in advance

A.C.Sant Anna

Original Post

Rather than start a new post I'd thought I'd add to this one. I have a simple two track setup power from the Z-4000. I haven't used the track much over the past year. This weekend the z-4000 won't go over 3.3 volts on one channel - both outputs are the variable voltage 1 and 2 outputs. One channel will increase to 15 volts or so and power the locomotives but if I increase the power going to output2 both left and right channels will cycle down until it shuts off. I have checked the track and connections and can't see what the problem is?     

Confusing, is this through a TIU or z-4000 alone?  If the Z-4000 has an issue powering track by itself you have a defective channel on the Z-4000 that needs to be repaired.  If the Z-4000 works fine by itself, the TIU has a shorted channel most likely.  Are you getting an overload signal on the Z-4000?  G

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Sorry, the connections are on the fixed voltage channels. The z-4000 works fine when not connected to the TIU and there is no overload signal when not connected to the TIU. The TIU was replaced last year so baffled why it would fail now as I have hardly used it. Is there anything that can be checked or a fuse replaced on the TIU or is it shot? When connected to the TIU the fixed voltage 2 won't go past 3.3Volts and cycles both outputs down to zero

If the TIU channel is shorting, the top suspect on fixed channels is the TVS protection diode.  They're a large thru-hole component and fairly easy to replace.  It's not uncommon for those to fail shorted.

Here's a picture of the TVS diode locations in the Rev. G, they're in similar locations on the later versions, but I don't have one apart to check.   Pretty easy to spot, they're large cylindrical components.

Well, to start you can just use an ohmmeter to check across them, a shorted one will read either zero or a very low resistance.  If you check all four, and the problem channel is markedly different, I'd simply replace the TVS.  As a simple test before you have the part in hand, you can just remove the problem one.  The TIU will operate fine, it just won't have the transient protection afforded by the TVS.

I was running the train on the one good track left just to demo it to some visitors but then that one remaining track stopped working. It says engines not found even tho they were working fine just prior. can't get them back to working. The one track indicates good power 21volts I think and the amperage is good. However, engine will only start up if I directly power from the transformer to the track. I'm taking apart the TIU tonite but it seems as maybe another issue has developed?  Where can the diodes be purchased? I think all the goold ole Radioshacks have closed around here     

I finally got to the TIU - are these soldered in place? As soon as I can find my ohm meter I'll check them out. I have a DCS Commander so I hooked that up, the locomotive is found and starts up, however it won't run. I just have it from Dc Track power output to my track and put in DCS command mode but the loco won't move. I did try a couple of different locomotives and switching the cable around. So I'm wondering if it is in fact the TIU or something else?  If I hook the track directly to the z-4000 it will run locomotives fine. I did search the site last night for some help but couldn't find this particular problem and the DCS manual is pretty limited.

gunrunnerjohn posted:

Yes, they're soldered into the board.  If the TVS is shorted, that channel will be dead on the tiu.

If shorted it won't be dead, it will short the transformer. G

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GGG posted:
gunrunnerjohn posted:

Yes, they're soldered into the board.  If the TVS is shorted, that channel will be dead on the tiu.

If shorted it won't be dead, it will short the transformer. G

Sound dead to me, that's what I meant.

gunrunnerjohn posted:

If the TIU channel is shorting, the top suspect on fixed channels is the TVS protection diode.  They're a large thru-hole component and fairly easy to replace.  It's not uncommon for those to fail shorted.

Here's a picture of the TVS diode locations in the Rev. G, they're in similar locations on the later versions, but I don't have one apart to check.   Pretty easy to spot, they're large cylindrical components.

With the talk about loose connections plugs in another post, would the 6th nut on the bottom be considered loose?  To me it looks like the nut is not tight.  I have not opened mine up, it has been put away for probably 7+ years, but will be coming out this fall as I am almost done with all my track.  Want to make sure what I need to look for.

Thanks

Probably, that was an old Rev. G TIU that I was working on when I annotated it with the TVS positions.  However, you'll notice that the wires are soldered onto the ends, not just secured with nuts like the later versions.  The clue is there are no fuses, all the later versions have the 20A fuses. 

The only downside of a loose jack in a Rev. G is... a loose jack.  It wouldn't affect the actual connection in this version.

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