I bought this subwoofer for 60€ as used but in perfectly working condition.
I opened it up to check the insides and found several capacitors that had already started going bad: ESR was high and capacitance has dropped bellow 20% tolerance. I am mainly talking about the ones being near the 2 transistors in the photos.
The 2 complementary NPN and PNP transistors are slightly discolored from heat and the area on the PCB indicates that they get quite warm. But they tested good and the sub is working, so I didn't replace them. I tried to bend them to make sure they are not cooking the new caps.
The transistors are D2531 and B1642. The sub woofer is based on the STK404-120 hybrid power amplifier and C4570HA operation amplifier. It relies on the TA7317PG for its protection and the bridge rectifier is RBV-402.
The old caps were Jamicon SK 85C. So this is how these Yamaha subs are so cheap for their specs and sound quality. They save on the caps by not using Japanese capacitors and even worse using 85C caps even in places where they are expected to get a lot of heat and not enough airflow.
I decided to do a full recap. I mainly used Rubycon YXF, Nichicon HE and Panasonic FR. Unfortunately I was out of stock for 47uF value and had to use 85C caps there. But that area of the PCB is not near parts generating heat.
I also plan to replace the 2 6800uF primary caps with 2x 10.000uF ones hoping this will enhance the dynamic response of the sub woofer.
Some pics attached before the recap.
I opened it up to check the insides and found several capacitors that had already started going bad: ESR was high and capacitance has dropped bellow 20% tolerance. I am mainly talking about the ones being near the 2 transistors in the photos.
The 2 complementary NPN and PNP transistors are slightly discolored from heat and the area on the PCB indicates that they get quite warm. But they tested good and the sub is working, so I didn't replace them. I tried to bend them to make sure they are not cooking the new caps.
The transistors are D2531 and B1642. The sub woofer is based on the STK404-120 hybrid power amplifier and C4570HA operation amplifier. It relies on the TA7317PG for its protection and the bridge rectifier is RBV-402.
The old caps were Jamicon SK 85C. So this is how these Yamaha subs are so cheap for their specs and sound quality. They save on the caps by not using Japanese capacitors and even worse using 85C caps even in places where they are expected to get a lot of heat and not enough airflow.
I decided to do a full recap. I mainly used Rubycon YXF, Nichicon HE and Panasonic FR. Unfortunately I was out of stock for 47uF value and had to use 85C caps there. But that area of the PCB is not near parts generating heat.
I also plan to replace the 2 6800uF primary caps with 2x 10.000uF ones hoping this will enhance the dynamic response of the sub woofer.
Some pics attached before the recap.
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