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Hi Group,
I have a Technics AVG Control Stereo Receiver SA-EX800 that after 5 - 10 minutes goes into "Overload" and shuts down, I have to power it off, turn volume down and turn it back on.
I just spent $170- on a new power supply, transformer and integrated circuits to control both, but that didn't stop the problem.
I can't turn the volume up more than about 1/4 % (of it's total amount of volume) or this "Overload" shows on the unit's screen.
I called the repair center and spoke with the Tech who worked on the unit, and he suggested perhaps bad speaker wireing [to the back of the receiver going into the speakers].
Last night I totally rewired the Receiver to Speakers (2) with new, solid coper core telephone wire, but that didn't change anything.
The Tech also said it could be a bad speaker (?).
I wired one speaker at a time, played a CD and listened to the speaker from 1 foot away, and heard no 'bad speaker or blow speakers', so I don't think it's a speaker problem.
- Both speakers sound clear with no distortion or other noise.
Would anyone have any idea what this problem could be???
I really can't play CD's this way, it's just useless.
I was going to say that it may be something with the speakers.
In a situation like this I would do some troubleshooting, some of this may be possible, some not.
Leave it on without playing anything and see if still overloads, if it doesn't, try headphones or different speakers to see if the problem is in the receiver or is caused by the speakers. It sounds to me like it's something in the amplifier section that you did not replace.
I assume it did not do this when it was new and you are using the same speakers?
First thing I’d check would be that the speaker impedance wasn’t too low. For instance some solid state amps aren’t comfortable with loads of 4 ohms and under. If more than one set of speakers are used a low impedance load might happen or even if using one set, depending on the speakers.
An "overload" warning is part of self-protection circuitry. The old way was with some variation of a thermistor detecting excessive heat, another is to check the output for signs of a short. There could be some sort of clipping warning going on as well. If you can turn the receiver (radio) signal up without the warning, but it happens on the CD, you may need an isolation transformer or resistance to lower levels. Speaker impedance is another good call. Low impedance may seem like a short to the system. Another possibility is the protection circuit itself is failing. One other thing to check is that everything connected to the mains is properly grounded and the wall socket properly wired and not reverse polarity. Don't rule out a call to the manufacturer. Sometimes there actually is an engineer in a back room.
I have had the exact same problem on mine. The issue was cracked solder joints at the base of the power transistors where they go into the motherboard. The heat sinks were not good enough to keep the heat away from the leads and the heating up/cooling down of using the stereo over and over eventually cracked those solder fillets. I can temporarily fix the issue by simply reflowing the solder joints but it will happen again eventually. What I did to solve the issue was to melt solder wick into that junction laying it along the surface of the lead and bending it at an L shape at the base, then adding extra solder along the wicks length both on the transistor lead and on the path on the mother board. Basically forming a little piece of solder wick into the shape of an L and reinforcing this solder junction. This extra surface area keeps that solder fillet from cracking again. Worked great. I still had issues with crackling when the unit was vibrated or bounced. This is caused by the long gold finger pins and sockets that fit the vertical boards to the mother board. To fix that simply solder all those junctions. Those types of pins are notorious for intermittent connections and soldering them will give you a solid connection.
I have had the exact same problem on mine. The issue was cracked solder joints at the base of the power transistors where they go into the motherboard. The heat sinks were not good enough to keep the heat away from the leads and the heating up/cooling down of using the stereo over and over eventually cracked those solder fillets. I can temporarily fix the issue by simply reflowing the solder joints but it will happen again eventually. What I did to solve the issue was to melt solder wick into that junction laying it along the surface of the lead and bending it at an L shape at the base, then adding extra solder along the wicks length both on the transistor lead and on the path on the mother board. Basically forming a little piece of solder wick into the shape of an L and reinforcing this solder junction. This extra surface area keeps that solder fillet from cracking again. Worked great. I still had issues with crackling when the unit was vibrated or bounced. This is caused by the long gold finger pins and sockets that fit the vertical boards to the mother board. To fix that simply solder all those junctions. Those types of pins are notorious for intermittent connections and soldering them will give you a solid connection.
I agree, it’s often cold solder joints/cracked joints, borderline iffy capacitors, or sometimes something with the speaker wire. I’ve had problems with all 3 over the years and it’s model-dependent.
"The heat sinks were not good enough to keep the heat away from the leads and the heating up/cooling down of using the stereo over and over eventually cracked those solder fillets."
That's an extremely common design 'problem', I think they do it on purpose.
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