# Replacing ZW Tranformer Carbon Rollers



## Nathan Plemons (Jun 24, 2011)

Hello all,

I have a 275 watt ZW transformer that works fairly well. When I dug it out of storage I noticed that the cord was in terrible shape. I replaced the cord but while I was inside the transformer I found that the carbon rollers on the two main handles are worn completely flat on one side. Repair parts are cheap so I ordered a set of 4 carbon rollers and a set of 4 rivets.

That's all well and good except that I have no idea how the mechanism comes apart! I was hoping to be able to replace the rollers without having to completely dis-assemble the transformer but it doesn't look like that's gonna happen. I can find the exploded diagram, although it shows me the parts it doesn't really show a step by step dis-assembly guide. Does anybody have any suggestions?

Thanks in advance!


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## gunrunnerjohn (Nov 10, 2010)

OK, first off, DON'T take anything apart! You can do this job with just the top cover off. Taking it all apart is a PITA.

Next, DO NOT TRY TO BEND THE HOLDERS! They are brittle and will break.

You can crush the old rollers with some needle-nose pliers. Next, cut the existing rivet using either some fine wire cutters, or if they're too solid like many of mine have been, use an X-acto saw.

I take the lazy man's way for the installation, I put the new roller on the rivet, then just crush the end of the rivet to hold it into place. *Servoguy* suggests soldering the rivet on at least one side for better continuity, probably not a bad idea. I haven't done this, but again there's that lazy streak... 

Finally, if the inner ones look good, leave them alone, don't fix stuff that ain't broke. 


Lastly, that comes after finally, here's the maintenance manual for your transformer: http://pictures.olsenstoy.com/searchcd31.htm?itm=671

If you have the ZW(R), there's a different manual: http://pictures.olsenstoy.com/searchcd31.htm?itm=672


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## tjcruiser (Jan 10, 2010)

Nathan,

No experience from me here (though great tips from John, above).

However ... please post some pics of the surgery, so that others can see / learn about this.

Many thanks,

TJ


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## Nathan Plemons (Jun 24, 2011)

Inner rollers were in fine shape so as you suggested I didn't bother them. I had attempted to clip the head off of the rivet using a set of diagonal cutters without much luck, I hadn't thought about breaking the carbon roller. I cut one off and was able to easily cut the rivet with my cutters. I was then able to put it back together with the new roller and rivets. I squeezed it with a pair of pliers but managed to squeeze it so tight it didn't roll, so I had to carefully pry the holder back apart with a screwdriver to get it to spin. I eventually got the right balance and it works like a champ. The other side went the same way.

I guess that was the easy part.... next I need to figure out the whistle.... I only have one whistling tender and it needs a new motor. It does work but there is so much slop in the motor bearings that you actually hear the motor turning more than you hear the whistle. The whistle technically works but only when the train is sitting idle. Without the whistle tender if I hit the whistle controls I can see the loco light get brighter and it speeds up. This makes me think the whistle rectifier is working ok and I just need to fix the tender.


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## gunrunnerjohn (Nov 10, 2010)

Actually, what you're seeing is the power boost provided when the shunt resistor is across the whistle rectifier, not necessarily the rectifier. There are two contacts for the whistle, the first puts a shot of DC about 3-4 volts out to pick the horn relay, then the second shunts the rectifier with a fairly low value resistor to boost the AC voltage and leave about 1/2 to 1 volt of DC under load.

Try this. 

Put a load on the transformer, I set it to 12 volts and use an auto headlight as a load, 35 watts is sufficient, that's what my old headlight is. 

Connect a voltmeter across the load and set it to DC. 

You should be measuring almost zero volts.

With the load on the 12 volt A or D output (you can test both independently), push the whistle button very slightly until you get a DC reading. It should be several volts. Push it farther, the light should get brighter and the DC reading should drop, probably below a volt.

If you don't get those results, you likely need a new rectifier. I'd retrofit a silicon diode rather than using the old Selenium disk, though I see that those are still available.


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## Nathan Plemons (Jun 24, 2011)

> Actually, what you're seeing is the power boost provided when the shunt resistor is across the whistle rectifier, not necessarily the rectifier.


Facepalm! I read about that and then totally ignored it. I was thinking voltage increase because DC would flatten out the sine wave and thus increase the light. I forgot all about the voltage boost that it's supposed to do because of the additional motor load. I'm at work now, I'll check it out as soon as I get off and see what I can find.


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## gunrunnerjohn (Nov 10, 2010)

Let us know what the symptoms are and what readings you get with the tests. That will tell us how well the transformer is doing and if you need a whistle rectifier fix.


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## Nathan Plemons (Jun 24, 2011)

Ok, I found my spare headlight bulb (everybody has one right?) I cranked the voltage on the DU side up to an indicated 12 volts. I put my meter on it in AC mode and it measured 11.8 volts without the bulb, not too bad on the accuracy department for an old transformer with a minimum of maintenance. I put the bulb on the track and kicked the meter over to DC mode. Sure enough I get 0 volts. As I tip into the whistle I can get the meter to read ~3.8 volts and I can hold it there. As I push the whistle switch further it drops under 1 volt, .5 or .2, can't remember exactly.

I did the exact same test on the AU side and got an indicated 12.0 volts dead on in AC mode. I got 4 volts DC with the whistle switch and then it falls off again to .5 or .2 when I push it all the way.

In both cases with the meter in AC mode, I see a ~5v increase when I hit the whistle. I guess this means the transformer is good and doing exactly what it is supposed to. 

Now as far as my whistle.... If the locomotive is non-existent, in neutral, or just BARELY trying to creep, the whistle works. It sounds lousy due to the noise of the motor, but it does work. If the train is moving at any kind of speed at all the whistle does absolutely nothing. Ideas?


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## gunrunnerjohn (Nov 10, 2010)

Sounds like the transformer is putting out the correct stuff, I'm guessing the horn relay on your tender is a likely suspect. I'd first check the pickups and wiring to see if all of that is solid, that's the easy and cheap stuff.  I'd also try the whistle by itself with say 8-9 volts on it, maybe you need to clean the commutator of it's motor and perhaps lube the bearings?


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## servoguy (Jul 10, 2010)

Nathan,
Did you bend the arms that carry the rollers so that the rollers are perpendicular to the transformer windings? This will make the rollers track properly. Also, I believe it would be a good idea to oil the rollers and the shaft that the rollers run on. The oil will not interfere with the operation of the rollers or electrical conductivity. I use 5W-20 motor oil because it doesn't evaporate very fast. Light oils and greases will be gone in a few months or years.

The copper oxide rectifier in the whistle control can be inop, and the loco will still speed up when you operate the whistle control. Best way to test is with a meter. Put the meter on DC and operate the whistle control. You should have a volt or two of DC when the control is in the first position, and less in the second position.

BB


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## servoguy (Jul 10, 2010)

Did you oil both bearings of the whistle motor? There is a bearing behind the impeller that you can't see. These motors tend to be noisy.

BB


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## tjcruiser (Jan 10, 2010)

Joining the discussion late, but I had posted some comments about the mechanics of whistle controllers a while back ...

http://www.modeltrainforum.com/showpost.php?p=47795&postcount=9

TJ


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## gunrunnerjohn (Nov 10, 2010)

Bruce, did you read the whole thread? He tested the transformer and found it works properly under load. FWIW, you won't get good DC readings unless you load the transformer.


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## servoguy (Jul 10, 2010)

John, I seem to remember I have tested a transformer w/o a load on it, but I don't remember for sure. I don't know any reason why a load would make much difference. It certainly wouldn't hurt to put a load on the transformer.

BB


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## gunrunnerjohn (Nov 10, 2010)

The DC will drop to absolute zero when the resistor is switched in, think about it.

I just did the test on a KW, the first step got 6.5 VDC, when the resistor switched in, it went to .037 VDC, in other words, zero.


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## Nathan Plemons (Jun 24, 2011)

Ok so I got the chance to play with it some today. I got the whistle working great as long as it is not moving. I put my train running on a loop and played with the tender on a siding. The tender doesn't care at all if the train is running or not. I had thought that maybe it was a voltage thing thus with the engine running it would give me trouble if the tender was not moving but it doesn't care. The only variable that seems to matter is the motion of the tender. I think I am just not getting good contact through the trucks when the tender is moving.

I can take the tender stationary and blow the whistle continously. As soon as I push it along the track it will stop, only picking up again when the tender coasts to a stop. Something is changing when the tender moves and the only thing I can think of would be in the trucks. I tried cleaning the rollers and wheels with rubbing alcohol and even a wire wheel on a dremel tool but it had no effect. I think maybe the spring loaded pickups are just really weak and its not maintainin sufficient pressure when in motion.

Thoughts?


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## gunrunnerjohn (Nov 10, 2010)

I'd agree, you probably have poor contact, either the rollers or the trucks grounding to the frame of the tender. You can try to remedy the frame ground by running a wire soldered to the truck up and attaching it to the frame of the tender. For the rollers, you need to make sure they're clean and have good contact. If the springs are weak, maybe they're not making good contact when they're in motion.


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## servoguy (Jul 10, 2010)

Have you cleaned the track with a ScotchBrite pad? I have never seen springs for the pickups that were so weak the pickups wouldn't work. There must be contact between the tender frame and the frame of each of the trucks and between the axles and the truck frame. Does the tender have metal trucks or plastic trucks? The fact that the whistle stops working when you move the tender makes me suspect dirty track and or dirty wheels. Are the wheels clean and shiny? 
BB


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## servoguy (Jul 10, 2010)

John, 
I ran a test on one of my KWs, and it doesn't take much load to produce some DC with the whistle switch in the 2nd position, and as you correctly state, the larger the load, the higher the DC voltage in the 2nd position. So theory and practice converge once again. 
BB


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## Nathan Plemons (Jun 24, 2011)

servoguy said:


> Have you cleaned the track with a ScotchBrite pad? I have never seen springs for the pickups that were so weak the pickups wouldn't work. There must be contact between the tender frame and the frame of each of the trucks and between the axles and the truck frame. Does the tender have metal trucks or plastic trucks? The fact that the whistle stops working when you move the tender makes me suspect dirty track and or dirty wheels. Are the wheels clean and shiny?
> BB


I doubt it is a track problem as the section I was testing on was brand new. It may yet be a wheel cleanliness issue though. Will get home late tonight and play more.


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