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I have a pioneer sx-950 with no sound output. All lights work

Customer Question

I have a pioneer sx-950 with no sound output. All lights work am am/fm signal work. I bought a power amp board with heat sink and I still have the same problem. I replaced protection board transistors and capacitors and I still have the same problem. When I turn it on I use a 12v power supply to engage the relay and when I turn up the volume I can barely hear the fm station through the headphones. When I put a 3-way speaker to it the woofer juts out like when you use a 9v battery to check speaker polarity. The only place i can think of is the power supply board. Has anyone gone through this before? Thank you for your help. Brian
Submitted: 6 years ago.
Category: Consumer Electronics
Expert:  Livep9 replied 6 years ago.

HeyCustomer

 

I ll be happy to assist today and thank you for using just answer. The first thing that i would do is look at the pc board from the top and the bottom looking for any lose transistors ,cap,and jumpers also check out the soldering on the pc board.

 

Ok if everthing checks good check the capacitors in the powersupply make sure they are not blowed up , also you have a 10µf capacitor connected through the diode to the base of the D669A. That and the 1N4004 form a simple half-wave rectifier. The idea here is that, on power down, AC is lost at the transformer, so the 10µf cap discharges very quickly. This pulls down the base of the D669A and opens up the relay contacts pronto. Because of the (sorta) large ripple current across the 10µf cap, it is a prime candidate for replacement.

 

But again i would keep my eyes on the power supply capacitors.

 

 

Thank You.

Customer: replied 6 years ago.
Hi, I don't have a 10uf cap on the board. The 1N4004 is not on the board. I have a wz-140 500mw 14v and wz-130 500mw 13v zeners. The odd thing is that the receiver was working great two years ago. When I looked on the service manual parts list c12 should be a 1000uf 35v instead it has installed a 2200uf 35v cap. On c14 has a 47uf 25v cap when the parts manual says 220uf 10v cap. I'm not a pro tech by any means but I'm puzzled to the 47uf being on the board which looks original and my service manual says 220uf on c14. Thanks, Brian
Customer: replied 6 years ago.
Relist: I still need help.
Hi Smithy. can you help me with this problem? To add to the problem, I replaced three 2SC945 transistors on the protection circuit board. One of them was shorted and the other two were ok but replaced because I had two more. I checked the power supply board and everything seems to check out ok. I pulled all resistors transistors and diodes off circuit and they seem ok. The only thing is the capacitors but I can't believe that they would be the culprit of sending the speakers 15dcv to where the woofer juts out like testing the polarity of the speaker with a 9v battery. I bought a amp board with the heat sink and output transistors out of a working unit and I get the same symtom.The only thing left is the flat amp board and the tone board. Thanks Smithy. XXXXX XXXXX

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