MTH Z 500 Transformer has constant 18 Volt output.

Controller triacs have failed shorted, or the other controller circuitry has failed such that the triacs are gated On continuously. The result is that the wall wart AC output is passed through. 

Are the triacs replaceable or should I toss this thing? 

I have seen this many times, there is a single diode on the board that needs to be replaced.  The MTH part number is BB-0000057.

I've had the diode and the triac both fail on different units.  Fix is the same, replace the failed component.

I know what a Diode is but I am still not sure what a triac is. Shouldn't I be able to get a suitable diode at my local electronic store? I hate to pay 10.00 to ship a diode. Thanks for the input guys.

Is a triac the thing you turn the power up and down with?

The triac looks like this.

I thought that was a voltage regulator! DO these things have any sort of rating and am I right about the triac?

You have to replace the triac with the same part or at least a compatible part.  They have a host of specifications, voltage, current, gate sensitivity, etc.

 Tiacs are usually a common part. Basically a large transitor. If you can match the numbers, or look in a crossrefrence guide for a match you can replace them.

RRaddict2 posted:

I thought that was a voltage regulator! DO these things have any sort of rating and am I right about the triac?

They are most commonly used in voltage regulation. Yes, the specs vary greatly.

What rating of a diode do I need?

You should be able to open the Z-controller via 4 Phillips screws.  Takes just a minute.

Once open, I figure it will look like this -  a Z-750 controller but it ought to be similar.  Front and back:

It's not clear to me if you absolutely must remove the aluminum heat-sink plate to access the 3-pin triac (circled in red).  But if so, that requires unsoldering the 3 wires going to the adjustment potentiometer (red rectangle).

Then, as suggested, read off the lettering on the triac and order a replacement.  A triac of this ilk should be, say, $1-2.  You'll pay more for the shipping unless you find it on eBay and wait a couple weeks for it to come from Asia.  Unless someone comes forward with the exact part #, just post whatever lettering you find and one of us will extract the relevant numbers to tell you exactly what to order.

As for the diodes, perhaps someone can identify exactly which diode goes bad.  I count about a dozen diodes on the circuit board.  It appears there are only 2 types of diodes - 1N4002 and 1N4148.  These part numbers are labeled on the board.  These a ~5 cent parts.  Again, you'll pay more for shipping than for the part and both these parts are on eBay where they are a couple pennies each though you'll need to pony up 99 cents to get a "lifetime" supply since you apparently need only 1.

So to answer you question, I'd say "yes" it's worth your time to take it apart, identify the triac part number, order a replacement, and attempt a DIY repair before giving it to your buddy.

I must have an earlier version as mine doesn't look like yours. I have a lot less components and two triacs as pictured. Gunrunner has pointed me in the right direction to get these so a huge thanks to him and everyone here. After I replace them I will post an update.

Or a later version! ** Your board shows surface-mounted components (vs. through-hole components on my photo) which usually comes later.  Can you post a photo of the other side of the board?  I wonder if you'll see another pair of those devices on the other side; for example, the MTH TIU variable channel uses such a multi-transistor design instead of a triac. 

In any event, if you already ordered parts, for the record what did you get?

** Note.  It appears the current version of Z controllers labeled ZCONTROLLER  are universal to the 50, 75, or 100 Watt brick transformers.  As opposed to earlier versions labeled Z-XXX which imply a mating to the brick of corresponding wattage.  I suspect it's the earlier controllers that use the single-triac design while the later version is what you have and use an alternative design.

bbsfdl60 posted:

I have seen this many times, there is a single diode on the board that needs to be replaced.  The MTH part number is BB-0000057.

 As for the diode, I do not see this part in my Z-750 controller so perhaps applies to the newer ZController.

The MTH site suggests the generic part number is 1.5KE51CA which is a TVS or surge-suppression diode - widely available for 50 cents or so.

This thing cannot be repaired, as I don't know how they did it but the two triacs are part of the PCB and cannot be removed except for cutting or grinding them off.  I did just that but I think I damaged it to badly to repair I went to low and grounded off some of the silver on the PCB on one side and the other side I will have to mount it on top of what I have grounded down. If this is just to dissipate heat then I could solder some foil to the part I messed up. I will let you know in a couple of days when I replace the parts what happens. Luckily I am in a separate garage that is away form the house so I won't burn it down.  I will also post a pic of the other side when I get home from work.

The contro0ller is like $35, just buy a new one

It may be 35.00 where you are but no less than 50.00 here before tax so its off to fleabay.

RRaddict2 posted:

This thing cannot be repaired, as I don't know how they did it but the two triacs are part of the PCB and cannot be removed except for cutting or grinding them off.

Those components should be remove-able albeit a PITA.  I believe those are so-called DPAK surface-mount packages like this:

First de-solder/lift the two legs from their pads.  Then place your iron tip along the length of the tab and wait say 5-10 sec, it will melt the solder joint on the back of the package and the body will lift off the board.  Obviously the large "silver" area of the board acts as a heat sink stealing the heat from the iron making the job more difficult.  Your board might be salvage-able though I'm thinking some kind of solder-able thin copper foil might be involved instead of non-solder-able aluminum foil.

Yes, I'd like to see a photo of the other side of the board.

And, for the record, what part numbers did you order?

Stan is right, they do come off, you just have to use a high enough wattage soldering iron to be able to melt the solder on the tab and the heatsink.  My 70W Hakko has taken them off identical looking boards.  It helps a bunch to use a little solder on the iron to give better heat transfer to the board.

FWIW, you can also select a TO-220 triac with similar specifications and solder it to what's left, it's tab is longer and may cover the area you ripped up.

Or you may find the identical device available in your choice of package so just order the TO-220 case instead of the DPAK case.  It appears to me the board was designed to accept either.  There appear to be 3 holes for soldering the 3 legs, and a larger mounting hole for the tab - like a #4 screw.  Depends on how mangled the area is.  Heatsink compound/grease might be in the cards.  You need good heat transfer from the package to the "silver" area to keep the device operating cool.

I changed the triacs and it still doesn't work. I will just have to head over to fleabay.  Thanks for everything to everyone on this post.

Did you have chance to photo the other side of the board?  Or let us know what/where parts you ordered?

Just trying to help the next guy with tangible documentation/information who stumbles across this thread in a search...

I will post a pic of the other side. Gunrunner hooked me up with Digi-Key for the triacs.  They are part number IRFZ48NSTRLPBF, they cost 1.55 each. I don't think it can be a very big problem but if I knew what I was doing I could fix it.  I sent MTH an email asking if I could purchase a new board but I have not heard back from them.  I checked the triacs with a meter and on one side when I turn the know the voltage goes up and down but on the opposite side nothing happens. 

I could use a photo of location of diode on z controller circuit board that is known to fail mine has 2 triacs.

If you can't meter them, replace them both.  From the look of the PCB, I can't imagine one is more prone to failure than the other, looks like they are each handling half the waveform.

Does anyone know what causes the Z1000 to ‘blow’, and give out a constant 18 volts?

     After two years of happily powering Williams and MTH locos, fifteen minutes with my Lionchief mikado caused my Z1000 to go constant. Am l just unlucky, or do Lionchief locos create some electrical interference that upsets Z1000s? (the brick did not overload).

      Thanks,

          Geoff.

The top suspect is the triac (or FET) that passes the voltage, don't remember the exact part on the Z-1000, but it's possible to fix them.

I have had this happen 2 x and repaired them both times .   Their are to plates on the backside of the board and are connected by a resistor type looking thing that connects the 2 plates.  I am not a electronics repair person by any stretch of imagination I did see a photo on this  forum and the item has 5KE47 CA   and below it 9924E   the helpful person at the electronic store found these for me.  Note this is only on a Z 1000     750 and 500 are different.     Yes it went full voltage and this item repaired it for me.

Thanks for your swift replies! I looked inside my Z1000,  and hmmmm. Soldering is not a strongpoint of mine, so, rather than completely ruin a partially working Z1000, l will leave it as it is. I had a previously unused Z controller from an MTH 2-8-0 set. I now use this to power my normal locos, and keep the Z1000 to run the Lion Chief. It’s only a matter of unplugging three wires to change them over. But, does anyone know if the Z1000 failing was just coincidence, or is their some kind of feedback from Lion Chief locos that upsets MTH controllers?

    Thanks,

       Geoff.

I'm sure it was only coincidence, I can't imagine anything that the LC locomotive would do to force such a failure.

@Geoff H. posted:

Thanks for your swift replies! I looked inside my Z1000,  and hmmmm. Soldering is not a strongpoint of mine, so, rather than completely ruin a partially working Z1000, l will leave it as it is.

...

What do you mean by leave it as it is?  I don't understand the value/application of a "partially working" Z1000 Controller that puts out a constant voltage?

I've always wondered how hobbyists that don't want to solder or mess with electronic components decide what to do in these situations.  It seems there's a price point ...maybe $50 (?) where the hassles of shipping costs and/or traveling to a LHS with qualified repair capabilities relegates such items to the landfill?

90 percent of the failures in a Z-Controller is a failed (shorted) TVS.  You can clip one lead and see if voltage control is restored.  If so, replace the TVS.  A spike in voltage usually takes them out.  It's the Diode shaped device bridging the two silver pads at the bottom of GunnrunnerJohn's photo.

Sounds like the failures we see with the TIU, many of those are the TVS as well.

Thanks again for the information, and advice. I’ll take another look. If l can’t repair it myself, l’ll mail it to someone who can.

       Thanks,

            Geoff.

@Jon G posted:

90 percent of the failures in a Z-Controller is a failed TVS.  You can clip one lead and see if voltage control is restored.  If so, replace the TVS.  A spike in voltage usually takes the out.  It's the Diode shaped device bridging the two silver pads at the bottom of GunnrunnerJohn's photo.

@Roy O posted:

I have had this happen 2 x and repaired them both times .   Their are to plates on the backside of the board and are connected by a resistor type looking thing that connects the 2 plates.  I am not a electronics repair person by any stretch of imagination I did see a photo on this  forum and the item has 5KE47 CA   and below it 9924E   the helpful person at the electronic store found these for me.  Note this is only on a Z 1000    750 and 500 are different.    Yes it went full voltage and this item repaired it for me.

I'm not providing any new information, just summarizing to help the next guy who stumbles across this next year as the Z-500 thread title may be a mis-direction.

So for the Z-1000 Controller, if you get full-voltage out of the controller, disconnect (e.g., clip one lead) the diode.  No soldering required to do this!

If this restores operation then replace the diode.  Soldering required.  Probably want to confirm the labeling on the diode.  Earlier in the thread the MTH part number BB-0000057 was suggested; the MTH site identifies this as the generic 1.5KE51CA diode, widely available - 66-cents qty 1 at DigiKey.  Above Roy O reports his Z-1000 controller had a 1.5KE47CA diode which is a very similar part (slightly different voltage) but also widely available - also 66 cents qty 1 at Digikey.  You'll pay much more in shipping.

If disconnecting the diode does NOT restore operation, then the repair will be more challenging likely requiring replacement of one or two transistor-like devices with serious soldering involved!  And that would be a good time to simply replace the diode.

This O Gauge forum has been a great help to me. Lets refer to the Railking Z 1000 controller at this time.. When mine went full voltage I was shown the possible problem.  I unsoldered the little culprit, tested it like I do all other diodes and showed faulty as current flowed both ways. As I talked to the person at the electronic store he asked how I tested the diode and he responded that it was normal. He found this item, that he identified from my removed part and said voltage was different but should work and it did work,  So the question I have If in fact it is a diode why does it test faulty?  If is not a diode what in the blank blank is it called and how can it be tested removed?  As I previously stated I am not a electronics brain by any stretch!  I want go give special thanks to GG as he has bailed me out more than once, also many other people on this forum. Special thanks to all from a grateful old man.    God Bless   Roy O