Z 4000 Dropping Voltage question

Sounds like a short, is the red light flashing, what are amps doing?  If you disconnect the Z-4000 and raise voltage does it come up?  G

George is right, has to be shorting. Do you have trains on the track?

GGG is right on track (LOL) I had the same problem and found out that a train had derailed. Removed all my trains and still had same problem. Took off inputs from Z4000 at TIU and no problem. Shorted something in my TIU rev L on that channel only.

Curtis

Today, when I applied voltage, the Z 4000 would not come off of 0.1volts. There was some buzzing and clicking noises in the layout especially from lighted passenger cars.  No red lights on the Z4000 lit up and I had no voltage reading on the track. I moved the handle up and down several times and I got a normal voltage reading. (and I was able to run some trains)  GGG, I was about to disconnect the transformer from the track to see if the voltage would increase, but it started working properly. I will check the amps next time it acts up. The problem is intermittent and acts like a short, but the red overload lights never come on. I appreciate any thoughts. thanks

If you happen to be on a grade watch for the uncoupling components. On some cars I have the couplers sit lower than others and they don't like the transition from flat to grade, coming into contact with enter rail.

Have been doing some testing, and the Z 4000 is working erratically. Sometimes the voltage wont come up at all above 0.1 then it will jump straight up to 17. I also disconnected the power feed to the TIU and track and the same problem exists. This makes me believe that the issue is in the Z 4000. Strangely, sometimes it powers up just fine and all works as it is intended. Is there a way to adjust the output? Does adjusting the handle affect the voltage output? Any suggestions appreciated. thanks speperak

Quick question. You are NOT powering up the Z400 with the handles up are you?

CurtisH posted:

Quick question. You are NOT powering up the Z400 with the handles up are you?

You won't get any voltage if you do that, and the red light will be flashing away.  You have to power up the Z4000 with both handles at zero for normal operation.

Sorry forgot John. My mind was not entirely computing what the failing eyes were reading. Thanks

The "Does adjusting the handle affect the voltage output?" kinda threw me for a loop. Not sure how you get voltage without moving handle! Never seen that!

I think he clearly has a short, the "buzzing" and the low voltage on the transformer are pretty clear signs.

Thanks for your replies. First, I always have both handles down when I turn the transformer on. Curtish, I was referring to adjusting the handle tension or adjusting internally, not raising or lowering. Gun Runner, a short does seem obvious, but the overload light never comes on and the voltage wont come up even when I unplug the z 4000 from the layout. Keep in mind that this does not always happen. Sometimes it works normally. Is there an internal adjustment to the rheostat that may need tweaked?

I doubt it's an adjustment.  What does the current display say when the voltage stays low?

The voltage will stay at 0.1 when I raise the handle. Then it will jump up to 4 or 5 with handle all the way up. Some of the buzzing noise seems to be coming from led lighted passenger cars trying to come on when voltage is too low. At times, the voltage comes right up to 17 or 18 as normal and I can run trains and all accessories with no problems. For instance, I just turned the z 4000 on and raised the handle and it stayed a 0.1. I then lowered the handle and turned the z 4000 off and then back on. The second time I raised the handle it came right up to 18. Sometimes it will come up to 10 to 14 volts with the handle completely raised. The overload light never comes on.

I'll jump in here and say that some years ago I had one that did similar weird voltage things. It was the pot for that handle which had become intermittent. It is a pretty easy fix and mth stocks the part. I would start there because it beats shipping it back to mth for repairs. If that does not fix it, most any other Z4K problem will have to be done by mth however.

Rod

There have been previous threads about Z4K repairs, just do a search.

Rod

GGG posted:

Sounds like a short, is the red light flashing, what are amps doing?  If you disconnect the Z-4000 and raise voltage does it come up?  G

After trying that, if it acts properly, connect it to a single piece of track that isn't part of the layout and see what happens.  Then put one car with standard (non-LED) lights on the track and see what happens.  These steps should eliminate track and car/engine shorts as being the problem. 

Again, what does the current indicate when you open the throttle?  The buzzing from the passenger cars or anywhere else on the layout ONLY happens when there is considerable current flowing!

Ummh guys, earlier in the thread to OP stated: "I also disconnected the power feed to the TIU and track and the same problem exists. This makes me believe that the issue is in the Z 4000." 

I think he nailed it.

Rod

Uhh... I did miss that.  Obviously, it's an internal issue.  I think it's time to "pop the top" and see if something is loose.

I'm sure it is the potentiometer but it does not matter as MTH has not had the potentiometers in stock for quite some time, I know because I talked to JASON  about this and don't know when they'll be in as they have to find another supplier to make them for MTH!

what you can do is open up the transformer and disconnect the throttle potentiometer and connect to a VOM volt ohm meter and check continuity  they are 10k ohm pots but  make sure you unplug the potentiometers from the circuit board . while having the potentiometers hooked to you potentiometer connect the center meter lead to the ohm meter and the other lead to either of the outside potentiometer while watching the meter while varying the throttle the ohms reading should gradually go from 0 ohms or close to that up to 10k ohms !if you see any erratic reading jumping all over the place or go to infinity no reading at all your potentiometer is definitely defective and you need a new one!

Alan

10 ohms?  Are you sure?  I'd expect those to be a much higher value!

yes I checked with other mth asc techs and Jason from mth

Well, Thanks for all of the replies. I would like to switch out the potentiometer if I can get one. That seems like a likely place to start. For now, I have switched the power wires to the other side of the Z 4000 and that side works perfectly. If anyone knows where I can locate a pot (since MTH may not have them) I would appreciate it. thanks speperak

did you check it out with the volt ohm  meter as I suggested that will confirm your problem, I researched it for MTH  Jason but could not find anyone making the exact same potentiometer I purchased a wire wound one but that would not work as I tried it and had to get a used one from another transformer, plus recently I have heard of some tca clubs member layouts that are having the same issue and have had to take 2  z4000 transformers apart  to make one work potentiometer out of one that was good and  install into the  one that was not working!

Alan

Actually I recall these pots as being 10 K ohms or perhaps 10 meg ohms, not 10 ohms, but I don't have one in front of me here in Arizona. They should be easy enough to replace with a generic substitute from an electronics jobber. That's where I would look first, and I would take the defective one with me. I suggest also disconnect the 3 wire plug that runs from the good one to the upper board, and measure the resistance across the outside two posts just to confirm the actual value.

Rod

Here is a pic of the pot. The shiny round thing with the red/yellow/brown wires attached. Pretty standard stuff. 1/4" shaft. Solder lugs.

I think considering that Z-4000's are current production, and there are thousands of them out there in operation, it's pretty darn sad that MTH can't get their act together and get spare pots bought from somewhere. Not rocket science as they say. 

Rod

I'm still really hard pressed to believe it's a 10 ohm pot, that makes no sense in an electronically controlled transformer.

Here's the Z4000 schematic page for that section.  If that's a 10 ohm pot, I'll eat my hat!  It's connected between 24 volts!  I'm not buying it, 10 ohms would have 2.4 amps going through it!  That is not a 10 ohm pot!

John, see my earlier post above. 

Rod

If it was 10 ohms it would be dissipating close to 60 watts of power. Can you say "Dorito" ?

Rod

Can we say magic smoke?

Alan, for now I am just running off of the other half of the Z 4000 and it is working. The layout is coming down this weekend and I will try to get the Z 4000 working properly during the downtime. I certainly appreciate your suggestions about checking the ohms and will try that once I get things taken apart. thanks speperak

Just had another thought that may help to isolate the problem. If you "pop the hood" you will see where the wire harnesses from the two pots connect to the upper board that contains the voltmeters and ammeters. Simply switching the two connections will reveal if the problem follows the pot, or not. Easy!

Rod

Just in case it helps at all, here is what you will see when/if you open your Z4K up:

Rod 

Rod, thanks for the photos. From what I can see it doesn't look too complicated to swap out the pots (assuming that's the problem). They are relatively inexpensive if I can find one. I will post an update once I have looked further into things. thanks speperak

Looks like all you'd need is a long shaft linear taper pot.

Here's a 10K one, which is my guess for the pot value: 10k long shaft linear taper pot

There are plenty of others.  The only issue might be having to cut the shaft to length.

@speperak posted:

Rod, thanks for the photos. From what I can see it doesn't look too complicated to swap out the pots (assuming that's the problem). They are relatively inexpensive if I can find one. I will post an update once I have looked further into things. thanks speperak

Did you ever complete the repair of your Z-4000?  If so, can you share the information?

Thanks, Steve