Start Voltage not changing a thing... (Attempt at Speed matching)

[Mark W]

Evening all. 
I have a Kato SD40-2 (one of the originals) with a hard wired (and recently replaced) decoder who's brand I've forgotten and not visible anywhere on the decoder.  I'm sure it's either Digitrax or TCS, leaning slightly toward TCS.
I'm attempting to speed match (using Tony's method) to a Kato/Atlas SD9 (again an old mech, also hard wired).  The SD9 has a DZ123 and seems to respond to CV adjustments ok.

The SD40-2 however, seems to receive the update command as apparent by the locomotive 'jerk', however I've gone nearly the full range of settings 0-250 for the Start Voltage, but regardless, on speed step one, it moves exactly the same, whether 0 or 250. 
Granted, the speed and movement is actually perfect for SS1, that does me no good for speed matching because the SD9 is geared a bit higher. 

I've never set any speed tables, or anything fancy, I even did a factory decoder reset, but nothing. 

Any thoughts?

(All using MRC Prodigy Express via Mainline Program)

[peteski]

With most DCC systems you should be able to read back CV values (on the programming track or on the main).  Have you actually tried to do that to see if the CV actually retains the value written to it?  Also read back CV8 to determine the manufacturer's ID and cross-reference it in http://www.nmra.org/standards/DCC/mfgnumbers.html.

[ednadolski]

For some decoders, you might have to switch off BEMF and/or speed tables in order for the Start Voltage CV to take effect.

Ed

[Mark W]

Unfortunately the MRC Prodigy Express is pretty much the most stripped down you can get as far as features in a DCC System.  No CV read-back.
All other CV's I change have a noticeable effect, so I'm certain the system is at least capable of writing the value to the decoder. 

I also set BEMF to off (tried both CV61 if the decoder is TCS and 57 if the decoder is Digitrax).  When I set 61=0, the I no longer had movement on SS1 (I think pretty solid evidence the decoder is TCS).  Now it takes speed step 18-21 before the loco moves.  However still, changing the start voltage has no effect. 

[ednadolski]

I also set BEMF to off (tried both CV61 if the decoder is TCS and 57 if the decoder is Digitrax).  When I set 61=0, the I no longer had movement on SS1 (I think pretty solid evidence the decoder is TCS).  Now it takes speed step 18-21 before the loco moves.  However still, changing the start voltage has no effect.

I think if there is no good way even to tell what decoder it is, you may unfortunately be shooting in the dark.  It sometimes can be enough of a chore to match speeds even when you know what is supposed to work.  It sounds like you might even have a buggy or defective unit.  Replacing the decoder may seem like a drag, but in the end you could end up saving yourself more in time and frustration.

Ed

[John]

I would try this

http://www.members.optusnet.com.au/nswmn/not_respond.htm

http://www.digitrax.com/tsd/KB675/resetting-a-mobile-decoder-to-factory-settings/

[peteski]

I would pop the shell and try to identify the decoder before trying to reset it.

[jdcolombo]

Agree w/Peteski.  Pop the shell and ID the decoder.  Then we may be able to help more.

I assume you are actually programming CV2 (start voltage).  I ask, because sometimes it is easy to dial up the wrong CV number.  Does the SD40 respond to changes in CV 5 and CV6?  If not, you may have somehow "locked" the decoder settings, or you may have CV29 set incorrectly (e.g., for a custom speed table).  If it does respond to changes in CV5 and 6, then I've got no clue.

John C.

[djconway]

Two quick questions - what color is the shrink wrap on the decoder?  Digitrax has been using an orange shrink wrap on their decoders since at least 1996.
Is the decoder set to support Min, med, max or Speed tables, check the setting on CV29. 

[peteski]

Two quick questions - what color is the shrink wrap on the decoder?

Um, we have been trying to physically ID the decoder since the initial post.    Maybe asking one more time will be the charm.  I like the way you asked to look at the decoder in a roundabout way, asking for the shrink wrap color.    Good point. TCS decoders usually use green shrink wrap.

[Bendtracker1]

Not sure why Mark hasn't gotten back to this thread, but a week or so after his initial post, he brought the unit in question over, along with a second unit.
It turned out to be a TCS decoder, but I don't remember for sure which model the chip was, a M1 or a M4.

We worked on it for a while, never did find out why it wasn't working properly.  But we did get it closer than he had it.

End result we got it speed matched to his other unit.

[peteski]

Thanks for providing closure to this thread Allen.

[Bendtracker1]

Sure!