Switching to DCC control from bluetooth not always working - any ideas?

[Bob-354040]

I now have 5 locos fitted with HM7000 decoders+powerpacks and working via bluetooth on my NCE Powerpro DCC system. Very pleased with them and the sounds. All works fine on bluetooth. However I seem to be getting a recurring problem when I have come to restart somedays, whereby if a loco was left as DCC enabled and I switch to Bluetooth on the app and run like this for a while, I can switch back to DCC on the app but the loco then does not respond to the NCE system. I have to switch it back to bluetooth to get control again. This has happened a few times now and the only way I can find is to shut down the app completely, turn off all power and start again. Then the DCC works via the NCE powerpro. Any thoughts please?

[WilliamDavid]

Could be noise from the power source corrupting the cvs, resetting correcting them.

Fitting a rc snubber might help.

[Fishmanoz]

First sighting of snubbers on HM | DCC and potentially TT:120!

For those not heard of them before - particularly on larger layouts (bus in excess of 10m in length) hence more likely in OO or O, stray reactance (capacitance and/or inductance) on the DCC bus can lead to very high voltage spikes occurring under short circuit conditions. These can be big enough to damage decoders. Best practice advice (see DCC Useful Links and then Mark Gurries who is the recognised NMRA expert) is to put twists in the bus pair and fit a snubber. The snubber is simply a higher power resistor and a capacitor in series soldered across the bus and is a low (frequency) pass filter which stops short and hence high frequency spikes.

Hence WD’s suggestion.

Easy enough to check - check CVs at the start of a BLE session, then again just before trying to switch to DCC operation and failing, then again on changing back to BLE. If there is no change, this is not the problem.

That said, there is no harm in fitting a snubber and, one day, it might stop a damaging spike.