The "Dither" Factor IN A TCS decoder for the Kato UP FEF #844

 THE Kato FEF UP # 844 uses a K6D4 drop-in decoder. With this decoder you can't manually control the BEMF feature which causes the steam locomotive to start too fast and lunge out of control at times during operations. To correct this, the BEMF must be set to zero. (CV 61=0). The factory setting is to leave the BEMF on. (CV 61=1).

You then must adjust  CV's 56 and 57 to actually obtain very slow speeds. This is very similar to the feature of CV 61 (BEMF) in Digitrax decoders. CV 56 and CV 57 must manually be adjusted in the Digitrax decoders to slow down the speed of the locomotive.

In the TCS decoder for the UP FEF #844, initially set CV 56 to 3 and CV 57 to 25. You then can adjust CV 56 and CV 57 in increments to obtain the desired speed results that you are looking for. It is all a mater of trial and error.

You can also set CV 57 to 0 to turn off the "dither effect" to see how the locomotive works with this CV turned off.

The excerpt below is from the TCS Website.

"Dither is digital pulse power. It is similar to "pulse power" that is used on DC power packs. It helps overcome the "stiction" of locomotive mechanics. With CV56 you control the frequency of the pulses and with CV57 you control the amplitude of the pulses. It provides better and smoother low-speed performance. Dither is especially helpful on locomotives that have high starting friction. There are two parameters that control the operation of Dither in TCS Decoders. Program the frequency of the additional pulse by putting a value in CV56. A value of 1 will give the highest frequency of additional pulses per second. We recommend starting with a value of 3 in CV56 which is the factory default. Values of 1 thru 255 are valid. Most locomotives will work best with a value of 3 in CV56. Typical values are between 1 and 10. CV57 controls the amplitude of Dither pulses. We recommend starting with a value of 25 in CV57. Then adjust CV57 up or down 5 at a time and test operation until you you find the value that works best for your loco. Valid values are from 1 to 255. (1 being the lowest amplitude pulse and 255 being the highest.) Most locomotives being manufactured today will work very nicely with a value between 15 and 35 in CV57. There are some older locomotive models that could benefit from a higher value of Dither amplitude in CV57. For some older locomotives that are particularly sticky a value of 75 to 90 might be necessary to help smooth the slow speed response. When CV57 has a value of 0, Dither is disabled. When CV57 has a value greater then zero it is active. It is active through the whole speed range and in all speed step modes (14,28,128). It is active with user loadable speed table, Vstart, Vmid, Vhigh. Try experimenting with Dither to achieve better low-speed operation. The effect will narrow the window between what point the locomotive starts to move and at what point it will stay running. There are two parameters that control the operation of Dither in TCS Decoders. Program the frequency of the additional pulse by putting a value in CV56. A value of 1 will give the highest frequency of additional pulses per second. We recommend starting with a value of 3 in CV56 which is the factory default. Values of 1 thru 255 are valid. Most locomotives will work best with a value of 3 in CV56. Typical values are between 1 and 10. CV57 controls the amplitude of Dither pulses. We recommend starting with a value of 25 in CV57. Then adjust CV57 up or down 5 at a time and test operation until you you find the value that works best for your loco. Valid values are from 1 to 255. (1 being the lowest amplitude pulse and 255 being the highest.) Most locomotives being manufactured today will work very nicely with a value between 15 and 35 in CV57. There are some older locomotive models that could benefit from a higher value of Dither amplitude in CV57. For some older locomotives that are particularly sticky a value of 75 to 90 might be necessary to help smooth the slow speed response. When CV57 has a value of 0, Dither is disabled. When CV57 has a value greater then zero it is active. It is active through the whole speed range and in all speed step modes (14,28,128). It is active with user loadable speed table, Vstart, Vmid, Vhigh. Try experimenting with Dither to achieve better low-speed operation. The effect will narrow the window between what point the locomotive starts to move and at what point it will stay running".