Bachmann basic "DCC Onboard" decoders fail to respond?

[duncanrinaldo]

Hello,
With 50 locos to put decoders in, they are not all going to get the Cadillac treatment...so I thought I could use the 6 Bachmann SD40s with DCC onboard just as they are.  Well, I would like to alter some CVs but I can't access them!

(I have the page from http://www.bachmanntrains.com/home-usa/newez/1_Amp_Decoder_Instr.pdf regarding the CVs for the basic DCC onboard decoders. And I know that the bit numbers are not right in the example on the PDF and have to be considered 0 to 7 instead of 1 to

.....but when I put any one of my Bachmann DCC onboard decoders on the programming track to program in service mode with my Digitrax Zephyr, I just get the "dnd" error which means no decoder is recognized.

Yet the programming track works with other decoders and the the locos in question all work with address of 03 and other factory defaults.

What gives? Any tips on getting access to the CVs on these basic DCC onboard decoders?

Thanks to anyone with experiece who cares to answer.

[the Bach-man]

Dear Duncan,
You will need a 1000 ohm resistor across the rails of your programming track to use a Digitrax system.
Have fun!
the Bach-man

[Jim Banner]

Only the Zephyr has this problem.  You can either use the 1000 ohm resistor trick, which will allow your Zephyr to read back from a Lenz type decoder (and thus allow it to program in its normal mode) or you can use "blast mode" programing which is a write only type programming that does not require any read back.