SD40-2 speed control

Did you try a Factory Reset on the locomotive?

I'd next check the tach encoder and strip.  If it's missing stripes, it'll run faster.  Maybe the spacing is wrong or the tach stripes are damaged.

If the tach tape on one has been replaced, it could be the wrong tape.  Might be worth opening both shells and comparing.  Also check cleanliness of the tape.

How much off is the speed?

John………I will do a factory reset

RJR……….

John…….

……………. Would the clearance from flywheel to reader matter? Speed is off enough so I        

             can't run as consist.

Clem

The spacing of the encoder and the number of strips are all important in determining the speed control.

Gap should be 0.75 - 1.25 mm.

I did a factory reset, that didn't help

Checked the gap and its .050

I noticed the tach reader was not all the way down in its bracket, pushed it all the down so it does not go above or below the striped tape. That helped a lot,  but it is still the fastest of the fleet. I can probably live with this.

What is the best way to widen the gap?

Clem

I figure .050" to be 1.27mm.  You don't want to widen the gap; a slight narrowing might be in order.  Can you alter the bracket seating a bit?

Again, whatis the speed difference?

The sensors do go bad, so if the tape is good, and has the same stripe count as the other similar models, I'd first try RJR's suggestion and drop it to about .040".  If that doesn't work, I suggest that it might be time to replace the tach sensor.

 I'm finding that some tach tapes need to be changed to get the speeds exact. Even from the factory, for some reasons, different engines are coming with the speeds not correct. If you have a spare set of tach tapes, try another one on top of the factory painted flywheel.

 I've got about five engines now that I've had to correct the speed on (out of a ton of them!). The first twenty engines I had bought, all were perfect. Maybe it's a percentage thing? All the tach readers are working correctly. Maybe the files are corrupt?

 I should mention for MTH, that I've bought these engines second hand and I imagine that's the reason they were whole-saled off to me.

 The stripes are fine but the engine is usually too fast. One G scale engine I have is too slow and I have not fixed or been inside that one yet.

It's easy to count the stripes on an engine with proper speed and compare that to the one that is going too fast.  Obviously, for the same model, it should have the same number of stripes.  Also, you can use a marker and repair any light or damaged stripes to insure an accurate reading.  If the tape isn't damaged, and it has the correct number of stripes, I can't imagine how replacing it could help.  OTOH, if it doesn't have the correct number of stripes, that WILL cause a speed difference.

Clem,

Are the stripes on a tape that's affixed to the flywheel or are they painted on?

If they're painted on, the paint may be too porous for the tach reader to register correctly. In this case, covering the painted stripes with a tape may resolve the issue.

Wasn't there some talk awhile ago that a software update or PS3 would include provision for slight speed adjustments?

 I've seen where the speed is just wrong, period. Usually when it happens it's too big to run in consist.

I used to ask why and now I've seen it!! So I fix it!!!

U guys tell me why it happens. New tape with corrected # of stripes = mmmmm good.

It pays to read everything posted here and keep an open mind.

I would suspect that would be a fairly big deal, and also change the nice scale MPH feature of PS/2 & PS/3.  Since all the speed timing is off the tach, I'm not sure how they'd easily do that.

Thank you Gentlemen

John- RJR- Barry- Joe

I set the gap at .030 , and it was still a little off, then I noticed again after I adjusted the gap to .030 that the reader was a tiny bit higher than the flywheel so I filed down the green board that the tach reader is made of and seated all the way down in the holder on the motor so it did not stick out above or below the flywheel. And that did it.. its now a perfect match. ran one lap (3 scale miles) and no change in spacing with two others of the same. I did not want to take another locomotive apart so I don't know the stripe count on the other units. When I get this one back together I will take one apart that is making noise. The stripes appear to be painted on and looked really good with a little shine to it, 24 stripes.

Once again Thank you 

Clem k

U the man!

I gave up on mine. The spacing didn't seem to change the speed. Good to know it worked here though.

 Can the processor's algorithm get corrupted?

Joe, it's not so much the spacing as the number of stripes. 

I assume that the program as loaded onto a loco can get corrupted, since programs on computers do.  Uploading a program from one of the other locos of same moldel # and downloading it to this loco might be worth a try.

Clem, just read you last post.  Glad issue is solved.  You're welcome.

Joe…….. a lot of the correction was done adjusting the tach stripe reader vertically

Clem

It's not only the number of stripes on the flywheel, but also the number of stripes that the tach reader actually sees.   The two can be different.

 I haven't noticed that type of change when playing with the spacing or aiming, myself. I will go back and take a closer look. I was amazed at how well the reader worked in some custom G scale installs I've done. Seemed like the reader's spacing just had to be in the ballpark. All the tach tapes were custom made by me so maybe the spacing was more critical than I thought?

 There's no way to tell if the readers missing the stripes? I can only adjust them and see if there's a positive reaction.

 I have an engine that I got that the board's speeds are fast. I've even swapped out the boards, sound files, tach reader, tapes, etc. The higher speed follows the board's?????

If it follows the board, I'd say it's possible the op-amp on the board or it's associated circuit may have an issue.

 I now have another G scale MTH engine that I got at least second hand that's way too slow (15%??). She runs very smooth and no noises or binding. I'll be interested in learning what she's doing. This will be the second G scale that is off in speed. The other named in the post above, is too fast?

 Seems like it's just too easy to swap out the tape. If something else is wrong the tach tape swap won't cure it, right? Maybe I just get lucky sometimes?

Are you sure the gear ratio just isn't right for the tach tape?

both are stock MTH G scale engines with stock sound files.

I have a couple of others that are off too. I should mention that it's a very small percentage of the total # of engines, and they were bought as rejects.

 I just like to tinker!

remember this one?

https://ogrforum.ogaugerr.com/topic/ps3-tach-gap

They still could have screwed up.   Key would be finding another identical locomotive and comparing the speeds.

 I have a fleet that I run to match my speeds with. I like to run long trains with helper engines in consist.

 I also run in G scale with several other brands that have been custom upgraded to PS2.

(I have several MTH G scale identical engines and others)

If you have identical engines, have you checked to see if the tach tapes are identical on them?

 The G scale Dash 8s are (look to be) painted flywheels. I will have to go back in and check. I didn't think they hand painted each flywheel? You would think that they'd be correct. But hey! I'd believe anything.

The other issue is the tach reader face can pick up dirt and require cleaning.  G