JSpencer Posted March 31, 2016 Share Posted March 31, 2016 Hi I obtained a DCC sound fitted Bachmann class 20. It has a 21 pin loksound chip. I think its a 3.5 but cannot confirm. As brought, it moved off like a scolded cat. But I soon put some values in CVs 3 to 6 that gave it realistic acerleration and excellent low speed control. The problem occurs when I want to start running the loco just above slow speed (say above 15mph on the controller). For some reason rather than accelerating just until it reaches the speed I set, it carries on until it's running flat out. The Diesel engine sound also increases until it's flat out as well. Any advice on what needs to be set in the CV settings please? Link to post Share on other sites More sharing options...
dasatcopthorne Posted March 31, 2016 Share Posted March 31, 2016 Never heard of this before. How many speed steps are you using on the throttle? Dave Link to post Share on other sites More sharing options...
JSpencer Posted March 31, 2016 Author Share Posted March 31, 2016 This is handled by the PC software. It seems to suggest for this chip it is 255 as the software recognises the chip make and type. However When I tried to set the CV high V value anything above 64, the chip would not recognize it! Link to post Share on other sites More sharing options...
dasatcopthorne Posted March 31, 2016 Share Posted March 31, 2016 Sounds like you have a Loksound v3.5 chip. Max on CV 5 is 64 so set the max speed you want the loco to travel at by bringing down CVS to whatever level it needs to be at for this. Then set CV6 to half of CVS. Now go back and set CVs 3 and 4 to the acceleration rate you like. 4 is usually half 3 but you may like it lower. Dave Link to post Share on other sites More sharing options...
JSpencer Posted April 1, 2016 Author Share Posted April 1, 2016 Thanks, I will try that (I think I did try that, but does not hurt to try again) but find it curious that once I move the controller above a certain speed, she carry's on gradually accelerating until at full pelt. Link to post Share on other sites More sharing options...
RAF96 Posted April 1, 2016 Share Posted April 1, 2016 May be worth checking if DC running is enabled (part of CV29) as any signal distortion can be seen by some chips as DC and off she goes flat out. Link to post Share on other sites More sharing options...
JSpencer Posted April 1, 2016 Author Share Posted April 1, 2016 May be worth checking if DC running is enabled (part of CV29) as any signal distortion can be seen by some chips as DC and off she goes flat out. DC is disabled. I confirmed this as she won't run on DC. Could it be the PC software thinking the loco has 255 speed steps instead of 64? How does a DCC system send a signal for speed ? Link to post Share on other sites More sharing options...
Nigelcliffe Posted April 1, 2016 Share Posted April 1, 2016 DC is disabled. I confirmed this as she won't run on DC. Could it be the PC software thinking the loco has 255 speed steps instead of 64? How does a DCC system send a signal for speed ? Go back and check the values set in CV2 (min), CV5 (max) and CV6 (mid). If "mid" is set too high, its quite likely that a loco will reach top speed very early. Also check CV29 for which speed curve is being used (simple or complex). There are only three types of DCC speed instruction, 14 step (pretty much obsolete), 28 step, and 128 step. If the decoder is set to 28/128, then it doesn't matter whether the command station sends 28 or 128, the decoder will recognise either. 255 steps are an internal matter for the computer software. When the instructions reach the track, they are either 28 or 128 steps (or 14 if things were set to that). The resolution of the speed min/max/mid values (range 0-63 in a LokSound V3.5) has no effect on this, its purely the resolution the chip uses internally. - Nigel Link to post Share on other sites More sharing options...
RMweb Gold tarifa Posted April 1, 2016 RMweb Gold Share Posted April 1, 2016 Have you tried a reset CV8=8. Link to post Share on other sites More sharing options...
Nigelcliffe Posted April 1, 2016 Share Posted April 1, 2016 Have you tried a reset CV8=8. A very unwise thing to try on a LokSound V3.5 when the nature of the sound project is unknown. Older LokSound V3.5 projects will reset to "factory" which is probably not the settings needed for the sound project. Resetting all the CV's to sensible values for the sound project will be a long tedious affair when the correct values are unknown. If it is known to be a newer LokSound V3.5 project which resets cleanly, or a different decoder, then a reset might be sensible. - Nigel Link to post Share on other sites More sharing options...
JSpencer Posted April 5, 2016 Author Share Posted April 5, 2016 Well I finally got round to doing CV8 = 8 and it still gently accelerates itself to full speed once above 10 mph. Something very odd about this loco. Link to post Share on other sites More sharing options...
10000 Posted April 8, 2016 Share Posted April 8, 2016 My experience with Bachmann diesels are with non sound but here are some observations The 3 Function (ESU) Bachmann decoder does not support speed tables so only CV5 can be used to control speed. With a 0 -63 setting it is not precise enough for accurate top speed setting. BEMF needs to be turned off with many Bachmann to achieve actual top speed (many run slower than scale top speed when turned on). It can also cause unstable/erratic running with Bachmann locos. Link to post Share on other sites More sharing options...
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