In sci.electronics.repair Jerry G. wrote:
This can be a defective RF stage in the tuner, or an AGC fault. The
tuner, when defective is changed as a module. You would be best off to
order the service manual and follow it through, or give out the set for
proper service. Take care for serious safety issues when working in TV
sets.

This particular model tuner by the way, was made by Temic.

---
Met vriendelijke groet,

Maarten Bakker.