A large customer of mine went through two techs before sending this 9090DB to me in hopes of getting a faster and cheaper repair. The last two techs used fake parts and improper service techniques so now it's in my shop anyway...and with more damage a bigger bill than if he'd just had it done right the first time!
Worse still, the fault shown could have even caused a fire.
All sorts of parts are being counterfeit these days but few are targeted for fakery quite like discontinued audio power transistors due to their high value and scarcity.
ALWAYS buy from manufacturer authorized distributors and if the original is out of production and is only available from a grey market like eBay or Alibaba, use a modern substitute that you can purchase from an authorized distributor. The vast majority of audio transistors have a modern equivalent that offers equivalent or superior performance so why risk your reputation and the safety of your customers with fakes?
FAMOUS AUTHORIZED DISTRIBUTORS:
https://www.bdent.com/
https://www.mouser.com/
https://www.digikey.com/
https://www.alliedelec.com/
https://www.arrow.com/
https://www.newark.com/
https://www.avnet.com/
https://www.futureelectronics.com/
This is a huge problem for the electronics industry as a whole; please see the links below for more information.
"Semiconductor Counterfeiting is a Global Problem"
https://www.eetimes.com/author.asp?section_id=40&doc_id=1332064
https://en.wikipedia.org/wiki/Counterfeit_electronic_components
"Winning the Battle Against Counterfeit Semiconductor - SIA Anti-Counterfeiting Task Force"
https://www.semiconductors.org/wp-content/uploads/2018/01/SIA-Anti-Counterfeiting-Whitepaper.pdf
"Counterfeit Semiconductors: The Risk is Real."
https://www.youtube.com/watch?v=d_dxbXrcXac
"Warning Regarding Counterfeit Goods"
https://toshiba.semicon-storage.com/us/design-support/warning-regarding-counterfeit-goods.html
"Elliot Sound Products - Counterfeit Semiconductors"
https://sound-au.com/counterfeit.htm