ABC section causes loco to emit strange noise

[DanielP]

Hi,

I've just added a ABC section to the end of a siding by means of the Lenz BM1 module. The section is about 1 length of flexi track and the braking works as expected across a range of decoders and locos.

The strange part is that a Bachmann 47 with a Zimo MX638D decoder emits a strange low-level whiney noise as soon as it enters the braking section and the noise stops as soon as it leaves. It performs fine, slows and stops, although the stopping point isn't 100% reliable. The noise is present with the loco just sitting idle in the section. If the BM1 is bypassed then the noise stops immediately. Wondering if there are any suggestions on how to stop the noise? 

Thanks in advance.

[Ron Ron Ron]

Do you have the same decoder fitted in any other locos's ?

 

[DanielP]

No, I have a mixture of decoders but I don't have another MX638D. The closest I have is a factory fitted Zimo MX645P22 which doesn't exhibit the issue.

[SamThomas]

Regarding the stopping distance not being consistance - doe the MX638D have the "constant stopping distance" feature & is this activated ?

[DanielP]

Yes, in terms of the accuracy I might just have too high expectations. It's accurate at slower approach speeds and the stopping distance is only 75cm. 

Edited January 22, 2022 by DanielP
spelling

[SamThomas]

It was just a thought, but I have no experience of setting up Zimo Constant Braking Distance. However, I do with Lenz & have found that once set up thr stopping is to within a millemeter every time.

Maybe the top speed is set a little high ?

 

Still does not explain the noise - I'd be inclined to try another decoder.

[Ron Ron Ron]

As Sam says, try another decoder in the same loco.

That'll determine if it's an issue with the decoder, the loco, or with the loco and decoder combined.

[DanielP]

I have left all of the original capacitors and inductors in the loco, would it be worth removing these?

[SamThomas]

Definatly remove of bypass them completly.

 

Apart from the fact they are not needed for DCC historically they have been known to cause many issues.

[DanielP]

Removed the capacitors and inductors which didn't make it any better or worse.

Fitted a new Lenz Silver21+ decoder and the noise has gone.

[SamThomas]

A strange one indeed & although I'm not a member of the "Zimo Rules Club" I'm surprised you had issue with the Zimo.

 

Main thing is that it's sorted.

[DanielP]

I'm now wondering if it would be unfair to try and return the Zimo to the retailer as it only fails in one specific way and maybe only in my specific setup. I think I'll probably just keep until my next 21pin loco arrives and see what happens then.