Step in speed progression

[Sly401]

So far I have fitted 4 HM7000 decoders, one of which continues to give  me trouble.

Problem -
Loco  moves off smoothly until it  reaches a certain speed , then it suddenly slows down to something like half its (pre hitch) speed if the control is set high then it accelerates smoothly all the way to the speed set.
When decelerating it is smooth until it  hits a particular speed ( I would say it is the same as when accelerating ) then it jumps up to around double its (pre hitch) speed.
I can drive it smoothly and consistently if I keep the speed below the hitch point  ( around speed step 60) but of course its all low speed stuff.
If  I drive it though the hitch its  top speed seems slower than I would  have thought
Consistent  hitch whether using App or NCE powercab DCC
I observe an increase in amps on the NCE whenever it passes through the hitch


Things I have tried,
re-install profile
install a different profile
reset CV's
Speed steps 28, 128, custom speed step table
Motor tune (auto)
Tried various  emf  and PWM settings
Tried different  start mid and High settings
Fitted a different  motor to the  loco  no difference
Checked the idler gear  not split, and motion smooth

I had thought that this was something to do with shunting mode or brake function  but  not so sure  now.

This loco  has the chip hard wired, does that invalidate the  warranty ?

Any ideas to try ?

Thanks Paul G
 

[Britannia Builder]

This is a strange problem, but given all the things that you have tried it does seem to be a faulty decoder. It appears that when it reaches a certain output voltage some alternate path opens up to drain some of the current.

I don't think that wiring the decoder directly would invalidate the warranty - I should return the decoder to Hornby.

Regards, John

[96RAF]

I would examine the complex speed table CV values to see if there is an anomaly in speed step progression, especially at the 'hitch' point.

Normally chopping the plug off will mean the warranty is void as Hornby cannot plug it into their system to check it out. You can but try George on the direct email address and see what he says.