Hi all. I've got a Marantz SR4023 (stereo receiver) on the bench in protection mode. PS section. regulators, relays, diodes, resistors - all check out. I haven't found a single suspicious, burnt or discolored component, so I've started to debug the L and R channels amps and the protection circuit. I have removed the transistors for out-of-circuit testing and found weird hfe behavior with these KTC3200GR transistors. The first one, from the left channel measured 40, the second I've pulled out measured 85, and so did the 3rd (more than twice as much than the first). To my surprise, the parallel transistors on the other channel's amp circuit, had nearly the same hfe. It's almost as if the transistors were matched cross channel. The protection circuit has a couple of these too (Q512, Q612). These measured hfe was 435 !!!. Again, the same KTC3200GR trannies appear to be matched, but nearly 10 times hfe as the first two in the amp section.
I'm baffled. Is this normal?
What can substitute KTC3200GR that can be had with Mouser/DK/newark?
TIA.
I'm baffled. Is this normal?
What can substitute KTC3200GR that can be had with Mouser/DK/newark?
TIA.
Hello! Can be replaced with 2SC2240, KSC1845. The 2SC2240 is exactly the same, but due to age it is difficult to find genuine, while the KSC1845 is a modern replacement.
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Thank you @madel88.
FWIW I've found a bunch of KTC3200GR's on a scrap main PCB of a Harman Kardon AVR-140 carcass. They all had hfe around 430. I guess the trannies I've pulled out off the Marantz had all failed - other than two. I've replaced the failing transistors and it's out of protection mode now. I biased it as per the SM and it appears to be working fine.
Thanks for reading.
BTW, I've figured out the KSC1845 compatibility because HK used a couple 2SC1845 in the center channel instead of KTC3200GR like on the rest of the channels, so I've looked up a modern replacement and bingo!. Other than a 50MHZ transition frequency vs. the original 100MHZ, they appear compatible.
FWIW I've found a bunch of KTC3200GR's on a scrap main PCB of a Harman Kardon AVR-140 carcass. They all had hfe around 430. I guess the trannies I've pulled out off the Marantz had all failed - other than two. I've replaced the failing transistors and it's out of protection mode now. I biased it as per the SM and it appears to be working fine.
Thanks for reading.
BTW, I've figured out the KSC1845 compatibility because HK used a couple 2SC1845 in the center channel instead of KTC3200GR like on the rest of the channels, so I've looked up a modern replacement and bingo!. Other than a 50MHZ transition frequency vs. the original 100MHZ, they appear compatible.