you can't find the TVS because the Z750 was a different design of the controller.

Point being- the full stuck on behavior is likely a failed TRIAC, but it's behind the board on the heastink so you have to remove the screws and the heatsink.

Q2015L5

Catch 22 is, they may be long out of production. Hopefully you can find a few.

Thanks Vernon, I knew you or Gunrunner John would come through for me.

I thought it may be the TRIAC, as this was also one of the "suspects" when I had the trouble with the Z1000 board.

The only problem (beside it not being available) is I have to de-solder the control pot to release its legs off the bottom board, to separate the boards to get to the TRIAC.

Let the fun begin!!!!

I'll get back with the results of my attempt to fix these little suckers.

Thank you Vernon.

Peter........Buco Australia.

Vernon:    And now for the update as promised.

Well, as you thought, I did have some trouble finding that particular Triac, but in the end I persevered and found some at Element 14, a component supplier here in Australia (I think they sourced them out of England).

I pulled the board apart to get to the Triac, and carefully replaced it with one of the new Triacs. Put everything back together carefully, and I now have variable power coming out of this Z750!!!!!!

Only problem is.......at full throttle the Z750 is maxed out at 10V, where-as the power brick is supplying 18V to the controller.  I would have expected at least 17V at the track end.

And the other thing is......I need to have a "load" inline to get the 750 to register zero when in the "off" position - hence the lighted lock-on in my test photos.

I have not tried to use this controller to run any of my PS1 loco's yet, as I have BCR's in them, and I need to be sure they are being charged properly at the start-up phase to protect the boards in the shut-down mode.

I am coming to hate these inferior Z500 and Z750 controllers, and wonder just why MTH ever bothered with them.

Worst comes to worst......I will pull the boards out of the two Z750's, and replace them with spare Z1000 board's I have in spare parts. 

Peter........Buco Australia.

Your result is normal. What you might not have known- the Z750 system, instead of 18V bricks, some had 21V bricks (edit- maybe even 24V bricks?).  https://ogrforum.com/topic/mth...ller-puzzle-question

As such, the matching Z750 controller from such a system- the circuit is modified to then reduce the output max voltage to roughly 18V max with 21V input.

So when you put one of those controllers with an 18V input, you get a lower max ouput.

Again, the Z750s were unique and different- and well maybe not ideal when you mix and match.

@Vernon Barry posted:

Your result is normal. What you might not have known- the Z750 system, instead of 18V bricks, some had 21V bricks.

As such, the matching Z750 controller from such a system- the circuit is modified to then reduce the output max voltage to roughly 18V max with 21V input.

So when you put one of those controllers with an 18V input, you get a lower max ouput.

Great information....I knew the 750 gave 21V, and did not have a aux tap, BUT did not know that their controller was different than the 1000 brick controller (which does output 18V and have the 14V tap!)

Now, to figure out which controller one has? Wonder if it is marked on the unit - or some other way to identify?

Your information could also impact the answer to another question I posted: can you use a Z controller with an older Lionel transformer. It might depend on which Z controller!

Good info Vernon, thanks. Greg

Hi Buco glad you got it repaired yourself , also did you know you can purchase the whole board new from mthpartsandsale.com and has a better design and less failure part number is CONTROL BOARD COMPLETE / Z CONTROLLER / Z-500 / Z-750 / Z-1000 AD5200002!

only costs @40.00 from mth parts and sales.com

Thanks for that info Vernon....I really appreciate it, and for the link to the earlier discussion on the habits of these Z 750 controllers. I will try another power source that puts out 22V, and just see what the results are.

Thanks also for the info on the replacement boards Alan (Alan Mancus).....I already have two of these boards in my transformer spare parts bin that I am threating to use if this Z 750 doesn't start playing nice!!!

At the risk of repeating myself........what was MTH thinking when they manufactured these crappy controllers??

It flies in the face of the other stuff they manufacture such as the Z 1000 and the Z 4000.

I'll be back with further test results when the blood pressure settles.

Peter.....Buco Australia.

@Buco posted:

Thanks for that info Vernon....I really appreciate it, and for the link to the earlier discussion on the habits of these Z 750 controllers. I will try another power source that puts out 22V, and just see what the results are.

Thanks also for the info on the replacement boards Alan (Alan Mancus).....I already have two of these boards in my transformer spare parts bin that I am threating to use if this Z 750 doesn't start playing nice!!!

At the risk of repeating myself........what was MTH thinking when they manufactured these crappy controllers??

It flies in the face of the other stuff they manufacture such as the Z 1000 and the Z 4000.

I'll be back with further test results when the blood pressure settles.

Peter.....Buco Australia.

Probably the same things Lionel was when they made the CW-80......

These were made for starter sets as far as I know Peter. I'm going with planned obsolescence as the reason. At least they still have the parts for sale.

Bob

Thanks for the words of advice Bob (RSJB18).......mental note to self......NEVER BUY A Z-750 CONTROLLER EVER AGAIN!!!!!

Vernon: I found the original box the transformer and controller came in, along with the transformer "brick", which was still in the box.

You were right about the output of these early Z-750 "bricks"......this one is rated at 24V!!

Bottom line:  Even using the MTH 24V output "brick", the best I can get out of the Z-750 Controller, at full tilt, is 14 volts to the track!!

This controller is going back in its box, never to see the light of day again while it resides here in Australia.

Thank you Vernon for all of your assistance in helping me to get this "THING" up and running again, but in the end, it is a dismal failure, as far as I am concerned.

Peter......Buco Australia.

@Buco posted:

Thanks for the words of advice Bob (RSJB18).......mental note to self......NEVER BUY A Z-750 CONTROLLER EVER AGAIN!!!!!

Vernon: I found the original box the transformer and controller came in, along with the transformer "brick", which was still in the box.

You were right about the output of these early Z-750 "bricks"......this one is rated at 24V!!

Bottom line:  Even using the MTH 24V output "brick", the best I can get out of the Z-750 Controller, at full tilt, is 14 volts to the track!!

This controller is going back in its box, never to see the light of day again while it resides here in Australia.

Thank you Vernon for all of your assistance in helping me to get this "THING" up and running again, but in the end, it is a dismal failure, as far as I am concerned.

Peter......Buco Australia.

Pete- bad part for me is i bought a Z1000 from Trainz. When it arrived, I popped the box open quick, all the parts were there.

When I set it up, it didn't have aux power terminals like the 1000 does...that's when I realized I had a 750 in a 1000 box.

Too late for Trainz to make it right so now I own a 750....at least I know the failure points.

At least it's a 21v model.

Bob

Another "HAPPY" Z-750 owner.......sorry Bob, I can't stop laughing.

I thought things like that only happen to me.

Have a Merry Christmas and a happy New Year Bob.

Peter.....Buco Australia.

All I can add is that

Misery loves company.....

Weeeeeeeeeeeelllllllllllll......if one has several bricks, it is easy to tell which is which. If one has the controllers, is it best to just use the 1000 controller and consider the 750 controller a paper weight?

Or don't run trains with it, and just use it to control lights in houses and other accessories - then just toss it when it finally dies? Since it puts out low voltage, it is probably no good for trains.

Just a couple of thoughts, I have both types. Thanks for taking the time guys, to post all the info on these.

Much appreciated, Greg

@Buco posted:

Another "HAPPY" Z-750 owner.......sorry Bob, I can't stop laughing.

I thought things like that only happen to me.

Have a Merry Christmas and a happy New Year Bob.

Peter.....Buco Australia.

Yea...that's what happens when you have to smuggle the train boxes past the CEO and stash them in the basement before she catches on.

Merry Christmas and Happy New Year to you and Sue as well.

Bob

Hokie 71.......I can't stop laughing at your comment....so true!!

Bob....I know that exact scenario, especially when my delivery comes from Switzerland.

There is a lot of fast talking on my part, and "the dust" usually settles after an hour or so.....usually.

Such is life with a wife....twice as bad without one.

Peter.....Buco Australia. 

Ok so I have a z750 transformer however it came with the IR remote not the 750 controller. Maybe the 21v out put transformer was to be paired with the IR controller or vice versa with the 24v transformer (bought my secondhand) (seller may have been full of it and just put these together) I run a prewar 262e with electronic reversing unit and it runs fantastic, smooth as silk no buzzing noise from the motor and I replaced barrel reversing unit so again no noise. Plan on installing rail sounds, sound card in the tender.

Yeh Michael @Michael Roth:

I don't think there is anything wrong with the actual transformer bricks, be them 18V, 22V, or 24V. The problem lays with that dumb Z-750 controller.

I don't have a Z-500 controller, but I am thinking it's going to be as bad as its bigger brother.

Either way, I won't be wasting anymore time on them!!!  It's a Z-1000 controller or a Z-4000 transformer for me.

Peter.......Buco Australia.