Weird QSI Sound Decoder


A friend contacted me Friday about weird actions with a recently acquired ebay purchase.  It was an Intermountain U18B with Factory QSI decoder.  I was not able to help him via text message so he brought it to me on Saturday.  When placed on the track with direction set for forward the sound started up, but when increased to speed step 1 the decoder shorted out and shut down my Power Cab.  Returning to speed step 0 cleared the short.  When reverse was selected and speed step 1, the engine took off at a fairly rapid speed and there was no controlling it with speed control or emergency stop. The only way was to remove power and it returned to normal idle sounds.  I attempted to enable analog mode to see if it would run on DC and changed CV29.  The change took effect, but there was no sound or movement.  I performed the three stop QSI reset to default and everything returned to the same way it had been before I changed CV 29.  I do not recall what was in CV 29 after the reset, but all I did was change it to 35, I think. It was no speed tables, normal direction, Analog enabled, 28/128 speed steps, I don't remember if there was something else, but that should not have caused a complete shutdown. I also brought it up in Decoder Pro and could not find anything that could explain this behavior, especially since it as reset to factory settings, and it did give the verbal reset response.  I could not think of anything else to try.  We discussed replacing the decoder, but decided the best option was return it to the seller.

Oh when reading the decoder it said it was Version 7, which Decoder Pro confirmed.  I have 4 or five engines with QSI decoders and they did weird things somethimes, but nothing like this.  I have replaced all of the chips with the Version 7, and they seem to run reliably.

Just curious if anyone can explain what was going on other than a failed decoder.



kelly dorf

That sounds very much like a bad FET in the motor control. That can most likely be repaired by QSI.
Email me at QSindustries224@...