Having had an intermittently working chain counter for the past two years (it could not record properly the chain going down, but was OK on the chain going up), I share my two cents which worked in my case: I dismounted and opened the unit in the cockpit and sprayed it with « WD40 contact ». It worked like a charm since then. The same recipe worked on our Hydra 2000, which was acting and stopped working at times; I spread the contacts and all the electronic boards and all went back to 100%. Again, sure it doesn’t apply in all cases, but it worked in ours!

Guillaume 
Carpathia III, SM2K #293