"Clean" video head displaying signal interference?
 

Dear DigitalFAQ Members,

I recently found a low-use JVC HR-S6900U S-VHS at a good price and the signal quality surprised me very positively. The image output is generally clean, but the video has some white lines in some frames that caught my attention. After an attempt to clean the video head, the frequency of the white lines has decreased, but the problem persists.
Please, I ask for your help as this problem has been bothering me a lot and I don't know what to do. What puzzles me is that the cause of the problem shouldn't be the video head, as the previous owner said he didn't use the device much.
If possible, I ask for simple instructions as I could not find any professional in my city who would accept to carry out the VCR maintenance, the entire procedure must be done by myself and I’m new to all this.

Thanks in advance!