Pioneer SA-408, output distortion - diyAudio
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Old 29th March 2012, 01:14 PM   #1
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Default Pioneer SA-408, output distortion

I opened up my Pioneer SA-408 amp since it was dusty and vacuumed it. I paid extra attention to volume and balance controls since they had a tendency to set off a "scratching" sound when I touched them.



Now the right channel (on both A and B) is distorted and it sounds like the speaker is blown. I've obviously tried switching speakers and it is indeed the amp.



Now I am afraid I might have ruined my "new" amp. I've checked thoroughly and everything looks good. I see no torn connections or anything. I need help diagnosing this.
Here is a schematic for the amp that I found via google (but the quality is lacking): http://i.imgur.com/jXhyx.png


If it helps, I'll post pictures of the insides of the amp.
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Old 31st March 2012, 11:19 PM   #2
tony75 is offline tony75  Australia
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Join Date: Mar 2012
Location: Sydney
Hello

I am in the middle of doing a complete overhaul of one of these. It had quite a bit of hum and some scratchiness which I have now fixed.
For the schematic you should sign up to HiFi Engine, they have a good PDF of the schematic which upon blowing it up everything is quite easy to read.
In your case where I would start is to get some contact cleaner and clean the controls, all the controls, the volume, balance, function selector and all the others. It is a little tough to get to the innards of the volume control from the top, some disassembly may be required. Most likely the noise will be from some some rubbish blown into the controls.
Start with these steps and see how you go.
Depending on how you go I can guide you through some extra steps with this amp.
Cheers
Tony
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Old 30th April 2012, 05:15 PM   #3
Lemtree is offline Lemtree  South Africa
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Join Date: Apr 2012
Location: Port Elizabeth
Hi Tony

I have just picked up a SA-408 for next to nothing but with some issues. I would like to fix it myself but have no experience and I live in South Africa which posses some interesting complications.

I tried plugging it all in and I get a very bad hum on the right channel and I only get sound coming through the speakers once I turn the volume knob right up. At one point it just starts blaring and the sound is distorted.

The hum is constant on the right speaker on both channel A and B no matter what I do.

I opened the amp and found the BC307A transistor on the far left (when looking at the face) is actually split in two and the 2w 0.22 resistor has been replaced with a mesh of small resistors all soldered together.

I figure there is probably more wrong that I can not see but I wanted to order these two components so I could replace them hoping it sorted all my problems out.

The plot thickens however, MCM who I believe are the only suppliers of the RGC22.22 resistor do not ship to Africa

I am going to try and see if I can get BC307A transistor locally, it seems these are general purpose transistors?

After my long explanation, what I would like to know is whether it makes sense that these two components are the cause of all my problems or if itís probable I will have to source more components?

Regards,
Quentin
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