N
N_Cook
Guest
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.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
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.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/