Powersolve 33 volt chargers are repaired by M.R. Electronics. They are usually fitted to Bison 50 or Bison 80 stairlifts and a few others. After a period of time they fail in such a way as they start to provide erratic (pulsing) output, or the output voltage starts to drop below 33 volts. Don't throw them away as we can repair this item at a cost of £15