Funny decoder behaviour... **update**

[irishthump]

Guys, a curious little problem...

I recently fitted a Gaugemaster DCC25 to a Bachmann S4 switcher but noticed some erratic behaviour.
On 28 speed steps which is what I use on all my locos the S4 moves smoothly on step 1. (After I adjusted SV)
Accelerates fine up until speed step 6 or 7 when the motor seems to labour a little and actually slows until I reach speed step 12 or so when it reaches what seems be it's correct speed.

Now I know that Bachmann US outline locos don't have the best mechanisms but I replaced the DCC25 with a bog standard Hornby R8249 and this issue disappears. The loco was a little noisy but was the same with the DCC25.
BTW, this also happend with a Heljan Class 26 but at the time I put it down to the high current draw that Heljan's are known for.

It's not really a huge issue, I can use the DCC25 in anouther loco, I'm just curious as to what causes it. Could it be a BEMF thing? I no it's not adjustable on either of those 2 decoders but that's all I can think of.

Any ideas...

[Sunnysa]

Have you removed all the capacitors in offending loco/s?

 

 cheers

 

  Ian

[irishthump]

Guys,

 

I've finally got bottom of this issue! This was happening with all 3 of the DCC25's that I own, regardless of make an model of loco they were fitted too. I finally got round to checking

the CV which controls at which speed step BEMF cuts off and low and behold it was set to 25 on all 3 decoders. Step 25 on 255 speed steps equates to 7 or 8 on 28 speed steps so this all seems to make sense! I have no recollection of programming this CV at any stage and I have reset the decoders several times so I'm assuming it's a default setting.

 

Anyway, problem solved, and if anybody else is encountering this issue this might be something to look at.