Note that, for several years now, all of the major suppliers of decoders have included a capacitor or 'keep-alive' component to get the locomotive over trackage where continuity is poor between the track elements or where the locomotive's pick-up tires lose contact with the perfectly well powered rails. This includes all Paragon 4 releases to date.
QSI decoders are an early form of decoder of which I still have all but two examples....of perhaps ten that I purchased between January 2005 and the end of 2010-12 when QSI released the last of their models, the Titan (my memory says that the Titan was the last release, perhaps I'm wrong...). They were odd in their indexing which required multiple steps to programme individual sounds. But, their sounds were pretty decent, even by today's standards, and their motor control still stands up reasonably well. Years earlier, QSI had a court challenge from Mike's Train House (MTH, now about six years out of the HO market). MTH felt that QSI had infringed on fine motor control patents and took QSI to court. MTH lost. Meanwhile, the courts prohibited, or injuncted, QSI from using their own fine motor control until the matter was settled. Shortly after the case was determined, and again NOT in MTH's favour, SQI offered a plug-in module for all their decoders to correct the defect in motor control which their software had controlled. They charged $20 plus posting, if I recall. I corrected three of my decoders that way.
BLI's Paragon decoders are generally very good, especially their vastly improved P4s. I read of many lamentations over the P3 variants released from maybe 2013/14 until about three years ago now, so I declined to purchase any of those releases.
Finally, I found this person's site and contracted him to repair a Paragon (first version) NYC Niagara 4-8-4 whose QSI had quit. He is a good communicator, easy to deal with, quick turnaround, and did a good solid repair of my unit. I highly recommend his service if you ever wish to convert an problematic BLI (only) locomotive to P4 (which is what I did since it included the keep-alive component). Prices are reasonable, considering. His name, BTW, is Seneca Pearson...I think I have his last name spelled correctly, might be Pierson. Give him a shout!
