Sounds like the cylinder servo is out of sync.
RF55 is simply the UHF Channel Number set on the video.
If the video is connected via aerial cable to the TV, then you would tune a spare channel 'position' on the TV (eg. '0', '8' or '9' are commonly used), to this UHF Number. Alter the setting using your CH buttons on the handset or CH up/down buttons on the VCR.
Note. Channel Position is the Programme Position you chose on yout TV. UHF Channel Number equates to the UHF frequency between 21 and 68).
UHF frequency numbers generally range from 21 to 68. This allows you to tune the output of the video, away from any adjacent transmission frequencys, which could cause interference on from the video to the TV picture.
On your video I would initially try using CH21 or CH68 for the video output. If unsucessful just try other CH positions until interference goes, or switch to RF-- (ie. RF modulator off), and connect to TV with Scart Lead only and use TV on the TV's AV setting.
Cobweb, January 2005