N
N_Cook
- Jan 1, 1970
- 0
Just out of warranty - distortion on one channel and crackles. Positive
going excursions only on that channel, expecting blown o/p transistors but
all now check out ok. They are all buried under the heatsink , so needs
taking apart to monitor.
Expecting bad solder, RoHS, as solder joints looking like 20 yearold leaded
solder joints.
No bad solder found - bad layout design. The end of a low power +B wire link
ends exactly under a 3.3K 1/4W resistor laying right over it, so touching
the bend of the wire. Nothing visibly wrong when received but maybe
overheating of a 470R R19 resistor at a TO92 Q7 emitter. Expecting bad
solder I started tapping things and phut this insignificant 3.3K , R5 at the
collector of a TO92 Q1 burns up. I'm assuming its 3.3K as that was remnant
measurement and corresponding channel B is 3.3K. Both these separated
resistors are electrically connected in the low power section of the amp and
I was the final straw.
According to the owner the amp had been overdriven for too long , outdoors,
but no sign of that but perhaps enough general heat to flex something.
So for these amps bend any resistor away from the ends of any wire links.
going excursions only on that channel, expecting blown o/p transistors but
all now check out ok. They are all buried under the heatsink , so needs
taking apart to monitor.
Expecting bad solder, RoHS, as solder joints looking like 20 yearold leaded
solder joints.
No bad solder found - bad layout design. The end of a low power +B wire link
ends exactly under a 3.3K 1/4W resistor laying right over it, so touching
the bend of the wire. Nothing visibly wrong when received but maybe
overheating of a 470R R19 resistor at a TO92 Q7 emitter. Expecting bad
solder I started tapping things and phut this insignificant 3.3K , R5 at the
collector of a TO92 Q1 burns up. I'm assuming its 3.3K as that was remnant
measurement and corresponding channel B is 3.3K. Both these separated
resistors are electrically connected in the low power section of the amp and
I was the final straw.
According to the owner the amp had been overdriven for too long , outdoors,
but no sign of that but perhaps enough general heat to flex something.
So for these amps bend any resistor away from the ends of any wire links.
