Hi everyone,
I need to get in touch with someone who's familiar with Yamaha's
active sub model YST-SW800. Well, this unit features a switchmode
powersupply among with a high power class D output stage.
It came into my repairshop with blown switching transistors in the
primary (2SC4140). Replaced those and powered it up to find a high
pitched self-oscillating sound coming out of the unit. Don't know if
the sound comes from the smps or the speaker itself. Didn't dare to
run it for more than 2-3 seconds in case I blow the switch.transistors
again.
So I'm looking for any advice regarding what could be the cause of the
smps damage, like service bulletins or upgrades, or any explanation
why the unit oscillates like it does.
Any advice is warmly appreciated,
best regards
Stefan