TCS service mode issues All right, calling a spade a spade here. (sorry I am from the 50's) This page is focused on the WowSound decoders, since it is my theory they used the audio menu heavily during development and kind of wrote off the service mode performance and reliability. This subject has earned a page on the TCS site as an FAQ, right off if this is a common problem, it is a TCS problem, not something else, in general. my experience is that reading CVs is from unreliable to impossible, depending on the decoder. I have both NCE and Zimo systems, very good systems. When I do the same operation over and over, with identical voltage and current and I get different results, the issue is the decoder. I have noticed that it may be possible that you have to wait a bit between reads. The fact that not all CV operations are ACK'd is also disturbing. Programming track powerThe first thing TCS says is maybe you don't have enough power to your programming track in service mode. OK, I buy that, a common issue with early sound decoders (yes TCS is comparatively new to the sound decoder market). BUT WHAT POWER? My Zimo system has adjustable voltage and current for the programming track. I will experiment Motor not connectedThey basically indicate that the motor provides the ACK, and tell you to be sure to have it connected. Reading it, they make the statement that the decoder will always get the programming command even if you don't get an ACK. Have to call bullshit on this, from personal testing. If you do not get an ACK, keep reading the CV until you have convinced yourself that the number you put in is actually there. Here's the reason I use a bad word:"What this means, is that a command station or dedicated decoder programmer will always send programming commands, regardless of whether or not a decoder provides an acknowledgement. On the flip side, this also means that a decoder will also always accept and ac[t] upon any programming instruction(s) received, regardless of its ability to provide an effective acknowledgment."Come on guys, producing an ACK is simple, you have powered tracks and a motor which ACKS by pulsing the motor load to the tracks. Another way to blame the DCC system not the decoder. There are other suggestions about that you really are not in service mode, etc. the common mistakes people make. I will endeavor to try to characterize the voltage and current this decoder needs, and also do this with other decoders, but this is flakey with the wowsound decoders, period.