First of all pay close attention to the specific error message received. Many controls have different designations for the causes of different faults. You can like find a detailed description of the fault in a manual which can narrow your search.
Relating to feedback specifically
Problem: You get a fault immediately upon moving an axis, regardless to position or to speed, or you cannot reference an axis.
Things to investigate.
1) I recommend always starting with the cable in a situation like this. It will likely be your least expensive fix. This can simply be done by running a cable on the outside of the machine and seeing if you are able to move/referece an axis. If you can than you can either reroute the cable through the existing path or create a new cable path that would achieve better resistance to electrical noise.
2) If the cable does not fix your issue you likely have 1 of 2 issues.
a) a faulty readerhead: replace the readerhead or consult a service company that has the proper test equipment.
b) paticularly in the case of a scale not referencing. Many incremental linear scales have a reference mark selector via a shadow plate, magnet, or other method. Check both the location of the selector and the Dog or switch, and in the particular case of a magnet, make sure it has not corroded and lost its magnetism.
3) If you have verified that the above conditions are met and satifactory then there is likely something mechanical and would check for binding or slipping of a coupling.
Problem: You get period faults from the encoders that you can not trace to a particular location or procedure.
Repeat the above procedure:
Things to investigate.
1) I recommend always starting with the cable in a situation like this. It will likely be your least expensive fix. This can simply be done by running a cable on the outside of the machine and seeing if your errors are corrected . If they are than you can either reroute the cable through the existing path or create a new cable path that would achieve better resistance to electrical noise.
2) If the cable does not fix your issue you likely have 1 of 2 issues.
a) a dirty linear scale: carefully follow manufacturers rules for cleaning or send to your preferred repair company.
b)a faulty readerhead: replace the readerhead or consult a service company that has the proper test equipment.
3) If you have verified that the above conditions are met and satifactory then there is likely something mechanical and would check for binding or slipping of a coupling.
Problem: If you get very repeatable faults in the same location regardless to speed or load.
Things to investigate.
1) Cable first... Inspect encoder to see if linear encoder is scratched or dirty in the problem spots. If there is visible damage to the measuring standard than you will likely need to replace the scale. If you can clean the standard then try that prior to replacing.
2) If the Linear encoder is functioning properly than you very likely have a mechanical problem. Linear encoders are pretty "dumb" they really either work or they don't. If the measuring standard remains uncomprimised the electronics of an encoder are note likely to manufacture condition to throw a fault repeatedly for no reason what so ever.
What about drift? How big of a scratch do you need before it effects the positioning
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