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Old 7th February 2012, 07:20 PM   #1
diyAudio Member
Join Date: Feb 2012
Location: Oslo, Norway
Default Sony STR-V45L (need help hacking amp board)

Hello everyone!
I'd be glad if some of you could help. I'll try to explain this right on topic:

On the table I have this old Sony reciever/2-channel 180W amp. Everything in the box is removed except the transformer, power amp board and the power/speaker channel switch/ headphone boards. I think I've found the right and left input wires, but no sound when power on (no wonder).

If possible, I want to locate all the in- and outputs on the amp board so that I can use it with a tone control.
(Eventually, I'll need some additional wiring to interact with the cut wires. This might be tricky ofcourse, because of the complex PCB.)

Thanks in advance.

Here's the complete manual with diagrams: str-v45l.pdf

Last edited by Tommiduck; 7th February 2012 at 07:58 PM. Reason: regarding the manual
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Old 7th February 2012, 10:10 PM   #2
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Join Date: Nov 2004
Location: Germany
How did the poor receiver get into that state, I wonder?

I suppose the power amp is still wired up the the output terminals? When turning the unit on, the protection relay should click after a few seconds - does this happen? If it doesn't, you'll have to do some troubleshooting there - a defective power amp would be the most likely cause (check DC offset on both channels, maybe at L701/751 or wherever else), followed by problems with the protection circuitry / relay driver.

The power amp can burn up for relatively trivial reasons like bad contact in the bias adjust pot and resulting increased quiescent current.
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Old 7th February 2012, 11:27 PM   #3
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Join Date: Feb 2012
Location: Oslo, Norway
I've ripped it apart some time ago because i needed some parts.

Yes, the outputs are still connected. It used to click when i turned it on, but it does'nt now. I also remember something smoking up around the area of Q801 while some of the grounding on the front panel was not attached. Then I also got some kind of oscillating noise when turning the volume pot. I'm not sure when, or what went wrong.

Could be the smoke or the cut wires, and probably both. I'll check back later.

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Old 8th February 2012, 11:24 AM   #4
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Join Date: Feb 2012
Location: Oslo, Norway
All the resistors read fine on my multimeter. The protection relay turned on and i got some sound in the right speaker, but it quickly turned itself off.
Seems like a real puzzle.

Maybe it's possible to access the basic functions of the amplifiers by direct soldering on the PCB, and then add new switches etc.?
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