Dolly
New Member
Hello, this is my first post here. I am not an electronics expert but love to learn. I seek some advice.
I have a Marantz 2250b receiver. I've had it for almost ten years. It's been a wonderful-sounding receiver (in tandem with small 1980s TOA studio reference monitor speakers [rated 120w] and a 1970 Pioneer PL-12D-II turntable, in a very small house).
Up until recently, I've only brought the receiver in once for repairs four years ago, after the left channel went out. The speaker relay and a couple of capacitors were replaced, and the main power switch repaired.
Recently I started to hear intermittent crackling from the left channel. It often would go away after some time. Then one day, I heard loud popping/crackling noises from the left channel, and the receiver completely shut down after a big pop. No lights would come on when the power button was pushed.
I brought the deck to a technician, who discovered a blown 12v5a fuse and two shorted output transistors (2sc1343 and 2sa753). While in there, he also replaced 3 panel lights and the stereo indicator light.
I brought the receiver home, and fired it up. Again after some time, noise came from the left, and then no sound. However, this time the panel lights stayed lit, but no sound came out. I immediately turned off the switch and unplugged.
I called the technician. He said it could be my speakers that caused this problem. I agreed to bring them in along with the receiver.
This time, the technician found the receiver in "protect mode." He again found a shorted output transistor 2sc1343.
My speakers tested just fine. They were rated appropriately for the power of this receiver and had no issues that the technician could find.
He determined that the cause of the shorting output transistors was heat build-up at the heat sink, "due to stripped mounting hardware screw holes" that caused the screws to become loose on the output transistors on the heatsinks (all due to the advanced age of the receiver). So he "used larger hold-down screws" to re-mount ALL the transistors, made "bias and dc offset adjustments, tested all modes and functions."
This time, I brought the receiver home and ran it for 4 hours. At first I heard a little bit of minor crackling from the left, but it stopped. The system sounded great -- for awhile.
But a few hours later, I heard crackles and a loud pop from the left. The sound stopped, display lights went out, and then I saw smoke coming from the rear left of the receiver!! What a stench! Immediately I unplugged it, unhooked everything and took it outside to the garage.
After giving it a couple of days to rest, I decided to open up the deck and look inside where the smoke had come. The output transistor in the rear left heatsink was missing a mounting screw! And also there was a screw missing from the bracket holding down the heatsink on that same side. I was really surprised to see all this.
Again, I called the technician. And he tried to tell me it was my speakers that caused the problem again! What?? I told him the speakers were fine -- he tested them last time and they still function. The issue was that there was a *missing screw* on the output transistor 2sa753. He couldn't argue with what I saw. I took photos, I told him. There probably are some other things that burned up when this happened, but I couldn't see anything obvious when I looked inside. He agreed to repair the receiver again under repair warranty.
But I don't plan to bring it back to him after this.
Have any of you experts heard of overheating output transistors being caused by the screws working loose on the heatsinks? Or could this be caused by something else that he didn't find? Is it even possible for speakers to cause this kind of problem? I am happy to answer any questions if anything I've reported is unclear or needs more detail. Thank you for taking the time to read and respond.
I have a Marantz 2250b receiver. I've had it for almost ten years. It's been a wonderful-sounding receiver (in tandem with small 1980s TOA studio reference monitor speakers [rated 120w] and a 1970 Pioneer PL-12D-II turntable, in a very small house).
Up until recently, I've only brought the receiver in once for repairs four years ago, after the left channel went out. The speaker relay and a couple of capacitors were replaced, and the main power switch repaired.
Recently I started to hear intermittent crackling from the left channel. It often would go away after some time. Then one day, I heard loud popping/crackling noises from the left channel, and the receiver completely shut down after a big pop. No lights would come on when the power button was pushed.
I brought the deck to a technician, who discovered a blown 12v5a fuse and two shorted output transistors (2sc1343 and 2sa753). While in there, he also replaced 3 panel lights and the stereo indicator light.
I brought the receiver home, and fired it up. Again after some time, noise came from the left, and then no sound. However, this time the panel lights stayed lit, but no sound came out. I immediately turned off the switch and unplugged.
I called the technician. He said it could be my speakers that caused this problem. I agreed to bring them in along with the receiver.
This time, the technician found the receiver in "protect mode." He again found a shorted output transistor 2sc1343.
My speakers tested just fine. They were rated appropriately for the power of this receiver and had no issues that the technician could find.
He determined that the cause of the shorting output transistors was heat build-up at the heat sink, "due to stripped mounting hardware screw holes" that caused the screws to become loose on the output transistors on the heatsinks (all due to the advanced age of the receiver). So he "used larger hold-down screws" to re-mount ALL the transistors, made "bias and dc offset adjustments, tested all modes and functions."
This time, I brought the receiver home and ran it for 4 hours. At first I heard a little bit of minor crackling from the left, but it stopped. The system sounded great -- for awhile.
But a few hours later, I heard crackles and a loud pop from the left. The sound stopped, display lights went out, and then I saw smoke coming from the rear left of the receiver!! What a stench! Immediately I unplugged it, unhooked everything and took it outside to the garage.
After giving it a couple of days to rest, I decided to open up the deck and look inside where the smoke had come. The output transistor in the rear left heatsink was missing a mounting screw! And also there was a screw missing from the bracket holding down the heatsink on that same side. I was really surprised to see all this.
Again, I called the technician. And he tried to tell me it was my speakers that caused the problem again! What?? I told him the speakers were fine -- he tested them last time and they still function. The issue was that there was a *missing screw* on the output transistor 2sa753. He couldn't argue with what I saw. I took photos, I told him. There probably are some other things that burned up when this happened, but I couldn't see anything obvious when I looked inside. He agreed to repair the receiver again under repair warranty.
But I don't plan to bring it back to him after this.
Have any of you experts heard of overheating output transistors being caused by the screws working loose on the heatsinks? Or could this be caused by something else that he didn't find? Is it even possible for speakers to cause this kind of problem? I am happy to answer any questions if anything I've reported is unclear or needs more detail. Thank you for taking the time to read and respond.
