Hi, I'm having also the same problem.
After using the little tutorial "how to dismantle the thing", I was able to determine that it was the board with lights buttons that was faulty (I witnessed also that the lights went from 20 to 0 when it finally broked)
-> When I remvove the connector from that board, the rest of the buttons work perfectly (-,Menu,select,+).
-> As I dont have the tools I'm not able to determine wich button is faulty... -> Next step !
Just a few words in french in order to be able to find this topic.
Problème réparation de réveil HF3485 Philips : Les boutons ne fonctionnent plus. Le problème venait vraisemblablement d'un des boutons de la carte dédiée aux boutons lumière/volume et commutateur. une fois cette carte débranchée, le reste marche...