I found my sheet with the measurements of the 10K pot in the Z-4000.

I looked around, this TT Electronics P160KNPD-4FC20B10K looks like a good match.

P160KNPD-4FC20B10K Data Sheet

@Rigatoni Express Railroad posted:

I have a Z-4000 that reads 0.6 volts on the left side when handles are all the way down.

While replacing a broken right side handle, I tried to see if there was any adjustment that would allow the reading to go to zero.

Doesn't seem to be any adjustment.

Does the reading indicate a bad pot?  Pots are out of stock at MTH.

Is there an alternate comparable pot to be had?

Any info appreciated.   Joe

First, what is the serial number of your transformer? This determines the build date?

That said, recently, I performed the modification to a newer transformer that also exhibited the voltage leak and adding the capacitors did fix the problem.

That's not an adjustment- that's the typical voltage leak. You could attempt to adjust the pot until blue in the face it would NEVER solve that issue.

2 choices- either load the transformer with something like a light bulb.

Or

Perform the modification to add the capacitors to the MOSFET gate driver.

https://ogrforum.com/topic/z-4000-repair

and

https://ogrforum.com/...-a-z4000-transformer

@Vernon Barry posted:

You have what is known as voltage leakage. There actually is a simple kit that adds capacitors to the input of the gate drivers of the FETs and corrects the issue. However, since you are located where MTH techs and support could be a costly problem (I've read a lot of your posts and problems)  you are looking for external help. Forum post https://ogrforum.com/topic/z-4000-repair

I did my own and here is a picture

Here is an edited diagram

OK, so say you cannot or do not want to modify the transformer and I fully understand and support that.

What you do not want is a fixed value resistor. Just understand why here. Ohm's Law and basic math doing power conversion to heat. If you put a fixed value resistor it cooks off more heat energy the higher you raise the voltage. Somewhere between being a burn risk and maybe being a fire risk, this is not how to do it. Yes, most basic power resistors do change value as they heat up, but normally this is not enough to prevent damage or excessive heat dissipation.

What you need is a self regulating resistor. Guess what? They exist!!! It's called an incandescent light bulb. The logic here is, the filament is one resistance (low cold resistance) starting out. This would effectively short out the leakage voltage. However, once you start raising the voltage, the filament heats up (hot resistance value) and will then increase resistance thus actually attempting to maintain a lesser current that what the cold resistance would suggest. This gives the short we want to shunt the voltage leak, and yet that same lower value cold resistance automagically rises to a more reasonable level as soon as the filament rises in temp and begins throwing off heat and light. This is the trick why a properly designed light bulb doesn't just burn out instantly.

A typical example would be to use an automotive 14V lamp. A brake lamp would be the most current however, might kick off significant heat depending on how high of a voltage you typically run in conventional. So something somewhere between oh say a turn signal lamp bulb or other bulb might be far easier to source and more correctly not melt something or become a fire hazard or burn hazard. Again, really you just need a decent 12-18V rated bulb that draws enough power to fix the leak, and not so much power it's getting hot (burn risk) or melting something.

Thanks to both of you, John and Vernon, for your quick and helpful replies.    Joe

I just was trying to nip this in the bud before you went down a path of changing out a pot only to find that did not solve the problem.

Yes, while the Z4000 uses an analog pot for the handle inputs, it's still a microprocessor controlled digital transformer. There is a minimum starting voltage and it's way higher than 0.6V more like 5V. It jumps from 0V setting to 5V  when using the Z4000 remote and by handle on mine, I could not start below 9V when completely unloaded using the handles. Again, handle fully down, then slowly moving up, it stays 0 (reading 0.1V on my displays) right to 9-10V as the handle s moved further up. And there is plenty of "dead band" in the handle between 0 and first notch of power.

Also, the transformer will not boot up properly at power on and show the red LED warning indicator if the handles are not fully registered as being down at power on. If you had that problem, then OK, we start investigating the pot and gear timing relationship, but no, not for a 0.6V voltage leak when set to zero.

0.6V is normal and I've seen plenty do that much. It was the early versions that might leak as much as 1.6V or more that really needed the fix.

Again, I would just add some load- as simple as a light bulb to knock that down if you are having a problem. Otherwise, the mod will also fix it, but much more involved to open the transformer and solder in those tiny caps in the correct location.

Thanks Vernon. Looks like its best to just live with it. Shouldn't be a problem.   Joe

The voltage leakage problem on the 0398 transformers can be lessoned by adding a lighted lockon or lighted cars to the layout.  Otherwise, the capacitor mod is the next step in repair.  The trains will run fine with that low leakage output.