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JVC JA-S77 - Noise Issues

JMiP

JMiP

AK Subscriber
Subscriber
I have a JVC JA-S77 integrated amp that sounds wonderful except for a few issues. When I have no music playing, I turn up the volume to see if there is any static or noise of any kind coming from any of the input channels. Dead silent on the Tuner and AUX channels, but Phono 1 is noisy and Phono 2 is really noisy. By "noisy," I mean staticky, like a radio player that doesn't have a station tuned in. However, I have to get the volume knob a bit past the 12:00 position before the noise becomes present. Is this normal? Also, the music does not sound distorted to my ears, even at somewhat loudish volumes.

Also, when the amp is set to the AUX channel, the left speaker eventually gets so staticky that I can hardly hear the music. This happens at seemingly random times after the amp has been playing for a while and it seems to happen only in the AUX channel. Now, I *know* this is not normal.

I swear that I can hear the right speaker a tiny bit better than the left speaker when listening to music (Tuner, AUX, or Phono), but that could be my ears playing a trick on me.

Known history of this amp: I bought it from a fellow AKer who replaced the capacitors (and I think the resistors as well). I replaced the relay switch because the left side would always eventually stop working and the seller guided me through that troubleshooting process. Would the issues with the AUX channel be related to this? Or is this just a coincidence? Maybe I did a less than satisfactory job with my soldering in of the new relay switch?
 
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Hello JMiP. Found the SM here on HiFIEngine.com https://www.hifiengine.com/manual_library/jvc/ja-s77.shtml Looking at the schematic found the 2SC458 transistors that go bad by being noisy. Check out this thread on the worst transistors http://audiokarma.org/forums/index....ilure-prone-whatever-and-replacements.731653/ The 458s are used in 2 places. Also maybe the switches need cleaned (DeOxit treatment). Hope this helps. Will check back to see how it goes. Well check the soldering while you are in there.
 
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Thanks NAD80. I was able to locate those two transistors in the service manual that you linked to. It looks like it's just a matter of desoldering the old ones and soldering in the replacements, making sure that the new ones go in the same way as the existing ones.

Any idea of the function of those two transmitters on the board?

Also, looking at the instructions for testing/adjusting the main amp center voltage and the main amp idling current, any bits of advice there? I was able to test the voltage a while ago since I didn't need to hook my meter to anything on the board, I could just put them on the speaker terminals in the back. However, for the idling current, I was able to find the area of where to connect the meter, and was able to find the adjustment pots, but I couldn't figure out how/exactly where to connect the meter. Also wasn't sure where the positive and negative cables from the meter go as there isn't real clear indicator in the service manual.
 
A fellow AKer is sending me some KSC1845FTA transistors. He says that they are a good replacement. When I get them in, I'll try to carve out some time to make the swap.
 
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