ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi all, first post here so please be gentle.
I have been repairing hifi since before I left school (40+years) and, over the years have successfully repaired thousands of systems, including the occasional B&O.
So last month when a friend asked if I could have a look at his BS9000 Mk II, I agreed to see why it wouldn't play CD's. It showed all the symptoms of a sick laser pick-up so I took it back to my workshop to have a proper look. I did all I could to clean the lens in situ but to no avail.
Well this is like no ordinary player and I did a fair bit of dismantling before I discovered how to get the pickup assembly out - most of it unnecessary I now know!
Long story short, I ordered a replacement pickup which arrived a couple of weeks later; fitted it and.... nothing! The 'sledge' moved across to position 6, stopped and the lights went out. Now dead. A few checks revealed a o/c 100mA fuse on the transformer primary. A tentative try with an ammeter showed 250mA being drawn - hence the dead fuse! But why? Had I dropped a screw somewhere? Unlikely, as I am generally very careful and I had all screws accounted for. A quick search on here returned this thread and indeed, all 4 mosfet's are s/c. Panic over for now, at least I know why it's dead.
SO my question is.. what causes these to go? I am nervous about just popping in new ones until I know what is likely to have caused their demise.
Suggestions gratefully received, TIA.