In this episode Shahriar repair a Fluke PM6685R Rubidium Frequency Counter. The instrument shows highly unstable results and produces high-pitch noise when powered on. The high-frequency noises point to a problem with the DC-DC converter circuit in the power supply module. A close examination points to degraded capacitors. After all capacitors have been replaced, the noise issue is resolved. The instrument’s performance is then verified and calibrated against an external Rubidium reference. The agreement between the units is better than 10ppb.