Just had a few German prototype Marklin short wheelbase locos DCC-d with Doehler and Haass nano decoders. These locos have 800uF of buffer built-in feeding the decoder. One of the locos came dead on arrival and I had to reset the decoder to factory defaults. The loco now runs very well and crawls with zero jerkiness, but there is a slight flicker to headlights in the direction of travel. Everything is fine when the loco is standing still and the flicker in motion appears random. I also cannot read the manufacturer CV anymore, which I could just prior to the reset. My other similar loco has zero flicker and I can read back CVs using my NCE powercab. Do you think my decoder is shot in the offending loco... with 800uF of buffer, there should be zero flicker, right? Would like others more well-versed in the ways of DCC to chime in with tips before I have to open up the loco. Sadly, the installer tragically passed away recently and cannot be approached for help or clarification. Thanks in advance. Ajay
Hi Ajay, I have had problems reading back CV's recently, and discovered that even though I cannot read back CV's, I could write them. In my case it was a TCS M2 decoder on a Rokuhan shorty with a resistor in series with the motor to slow the speed down. What I found is I can reset that decoder fine, and program any CV's, but it was a slow process because the readback was not detected. So what I propose, is that if you have one that can read back CV's, write down on paper, the CV's for everything you need from the decoder you can read, and write those values into the other decoder one at a time, and see if it works. It probably will work fine afterwards. I have observed a normal cv readback is usually accompanied by small motor jerks, and if those jerks are too small, (because in your case the 800uF is absorbing the jerks by charging the capcitors, and in my case because the motor has a resistor preventing sudden motor jumps) that the command station is not seeing the confirmation of CV's being written) So before opening it up, give it a try manually imputting the CV's to match the good one. -Robert
I'm not Familiar with Doehler and Haass decoders, but i do know some decoders have to be programmed before connecting a Keep-a-Live. With that said you may need to disconnect the 800uF capacitor in-order to read or reprogram the decoder.
Thanks for your responses. I'm going to first try Robert's idea of trying to re-write CVs based on my other similar loco... then I'm going to reluctantly try opening the loco up and see if it is a contact issue. Regarding programming CVs, I have another loco with a D&H decoder (different model of decoder) with stay-alive capacitors that I have successfully changed CVs on. I'm hoping I don't have to disconnect the stay alive capacitor bank prior to writing CVs. We will see. Will keep y'all posted... Thanks, Ajay
