saabracer23
Super Member
I have a CR-1020 that made a wooshing noise and popping in one channel. I had just gotten it and only played it for maybe 5 minutes before turning it off and digging in. I’ve read the popping issue could be due to bad solder joints which I checked everywhere. I found the issue on one of the daughter boards in the preamp, pre module D
Transistor TR572. I traced a distorted waveform through the preamp section until I found where it began.
I could see that this board was worked on before as the transistor that was bad was an NTE part and one both board D and E there is a trace repair at the very top. The trace repair is in the exact same spot on both boards which I find odd.
Since I found the issue in went in for a full restore. All electrolytics changed, power supply rebuilt with new resistors, new bias trimmers, new thermal compound and insulators for the outputs, and reflowed pretty much the entire power supply section.
Anyways, the bad transistor measured on my Peak Atlas meter as a darlington instead of a silicon. I figured the NTE was a darlington.
I relplaced all 8 transistors on boards D and E so they were matching. The originals were 2SC1775 and 2SA872. I placed KSC1845 and KSA992.
After placing the new transistors the popping and wooshing was completely gone. I started burning it in to make sure all was good. It sounded amazing, for about 20 minutes. What a bummer. It started making really loud popping noises and out of both speakers now. I mean violent pops, they were scaring me lol. I thought maybe bad solder and started tapping everywhere and it didn’t help. On a whim I pulled both of the pre module boards D and E. (D and E are identical)
Sure enough, both of the number 2 transistors (TR572 on both boards) From each board have been damaged. They are now measuring as darlington transistors on my device, they’re KSC1845s.
What could be damaging these transistors?
Dan
Transistor TR572. I traced a distorted waveform through the preamp section until I found where it began.
I could see that this board was worked on before as the transistor that was bad was an NTE part and one both board D and E there is a trace repair at the very top. The trace repair is in the exact same spot on both boards which I find odd.
Since I found the issue in went in for a full restore. All electrolytics changed, power supply rebuilt with new resistors, new bias trimmers, new thermal compound and insulators for the outputs, and reflowed pretty much the entire power supply section.
Anyways, the bad transistor measured on my Peak Atlas meter as a darlington instead of a silicon. I figured the NTE was a darlington.
I relplaced all 8 transistors on boards D and E so they were matching. The originals were 2SC1775 and 2SA872. I placed KSC1845 and KSA992.
After placing the new transistors the popping and wooshing was completely gone. I started burning it in to make sure all was good. It sounded amazing, for about 20 minutes. What a bummer. It started making really loud popping noises and out of both speakers now. I mean violent pops, they were scaring me lol. I thought maybe bad solder and started tapping everywhere and it didn’t help. On a whim I pulled both of the pre module boards D and E. (D and E are identical)
Sure enough, both of the number 2 transistors (TR572 on both boards) From each board have been damaged. They are now measuring as darlington transistors on my device, they’re KSC1845s.
What could be damaging these transistors?
Dan
