Hi.
Does anyone knows a place in London or UK, where I could get some old audio equipment fixed ??
Or maybe anyone on here knows electronics ??
Thanks
Try DK in Mitcham
http://www.dkavs.co.uk
They have a long established branch near me in Horley which I've used a few times over the years. They repair all types of electronic equipment.
If it's a genuine Walkman, try a Sony Centre or a genuine Sony repair centre (check the Sony website). It's been a long time since I was a student working in a Sony Centre, but we used to take in a few older pieces of kit for repairs.