How 'almost immediately' ? If its OK for a couple of seconds then you have a fair chance of getting somewhere with freezer spray. That is a golden window of opportunity if so because its non invasive and it gets results. The same applies if the noise varies a little in character or amplitude as it sits there running.
If the noise is constant from the instant of switch on then its much much tougher.
Have a tap around with a plastic pen etc around the transistors.
Output transistors are the least likely suspects but you have an ace card, there are parallel pairs in each channel. That means you can remove one pair at a time and the amp will still run normally. Very very unlikely they are an issue though.
The drivers and pre drivers ! Your best chance here is just to initially swap them over channel to channel and see if the fault clears (because of heat as I mentioned earlier) or swaps channels.
The pre drivers are X421 and 423, drivers are X425 and 427 and the outputs X429, 431, 433 and 435
Look for any transistors that run hot. They would be suspects along with any components such as caps that were immediately adjacent to them.
If the noise is constant from the instant of switch on then its much much tougher.
Have a tap around with a plastic pen etc around the transistors.
Output transistors are the least likely suspects but you have an ace card, there are parallel pairs in each channel. That means you can remove one pair at a time and the amp will still run normally. Very very unlikely they are an issue though.
The drivers and pre drivers ! Your best chance here is just to initially swap them over channel to channel and see if the fault clears (because of heat as I mentioned earlier) or swaps channels.
The pre drivers are X421 and 423, drivers are X425 and 427 and the outputs X429, 431, 433 and 435
Look for any transistors that run hot. They would be suspects along with any components such as caps that were immediately adjacent to them.
Attachments
Hi Molly,
The noise does vary. It's actually two types. On is static-popping, no rhythm to it, the other is a kind of whine sound similar to a needle being dragged across an album on a TT an it too varies in pitch.
Here's a video I took when the sound started to happen. At this point there was more of this audible sound, not as much static-popping. Also, this was after the amp was on for 10-15 minutes. Now, there's more static and less of the sound.
A-X9Ampbadsound_zpsec8a2fda.mp4 Video by GD70 | Photobucket
Here's also the link to my thread on Audiokarma and some comments as to what to look for. Maybe combined forces will help and the next tech.
http://www.audiokarma.org/forums/showthread.php?t=598247
Glenn
The noise does vary. It's actually two types. On is static-popping, no rhythm to it, the other is a kind of whine sound similar to a needle being dragged across an album on a TT an it too varies in pitch.
Here's a video I took when the sound started to happen. At this point there was more of this audible sound, not as much static-popping. Also, this was after the amp was on for 10-15 minutes. Now, there's more static and less of the sound.
A-X9Ampbadsound_zpsec8a2fda.mp4 Video by GD70 | Photobucket
Here's also the link to my thread on Audiokarma and some comments as to what to look for. Maybe combined forces will help and the next tech.
http://www.audiokarma.org/forums/showthread.php?t=598247
Glenn
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That is some weird noise. It could be a semiconductor or a cap.
I honestly think your best hope with this is to attack it with freezer. That's something you can do yourself. Any good component will not be affected at all be the freezer, anything suspect would almost certainly change/alter the noise the instant it was chilled.
I honestly think your best hope with this is to attack it with freezer. That's something you can do yourself. Any good component will not be affected at all be the freezer, anything suspect would almost certainly change/alter the noise the instant it was chilled.
Thanks Mooly!
I'll pick some up and see what happens.
My friends brother use to maintain The band Santanna's equipment. When he heard that sound, he also said it could be a bad cap.
I'll pick the amp up this weekend and see if I can get any other info from him.
Thanks again!
Glenn
A bit of luck, I hope. A fellow Audiokarma member recommended a great tech about an hour from me and he will be passing my town and pick up the amp tomorrow! From what I've e been told he's very good and reasonable! Maybe a bit of light at the end of the tunnel, and he is also a JVC amp owner!
I'll keep the updates coming.
I'll keep the updates coming.
The new tech has the amp. When I told him what the previous diagnosis was, he said that's incorrect. If the power transistors were bad, it would not come out of protection. Since it is working, he suspects some bad transistors. He'll let me know later this week what's causing the problem. Fingers crossed!
I'd go along with that. Power transistors tend to fail in an all or nothing way... it wont be the outputs at fault. The smaller drivers can go intermittent though. My only nagging doubt on that if that is the case then its pretty consistent and not going worse to the point of total failure. So transistor or cap... it could be either. My instincts say transistor, but the evidence is pointing me more to a leaky/noisy cap.
Hi Mooly,
It's interesting all the different possibilities which can make it so frustrating. This tech has all kinds of test equipment and I have no doubt he will find the issue. Regarding the SK150a (GR), he said, oh yeah, if got plenty of those! I guess when you've been repairing gear for 40 years, you have an amazing stock pile of parts!
I'll post an update when he tells me what the problem is.
Glenn
Fixed and sounding great!
One small transistor on the output board! The tech also replaced two caps, though they were not causing the noise.
Here's the invoice of the work done. It's sounding excellent, running much cooler as well. After 3 straight days powered on, it was just warm, not hot like it use to be.
Thanks for all your gents!
Glenn
One small transistor on the output board! The tech also replaced two caps, though they were not causing the noise.
Here's the invoice of the work done. It's sounding excellent, running much cooler as well. After 3 straight days powered on, it was just warm, not hot like it use to be.
Thanks for all your gents!
Glenn
I know, amazing one little thing can cause such a problem. The tech had noticed an area on the board that looked like it had gotten quite hot. He used the cold spray method as you suggested to narrow down the problem.
Next I'll bring him my JVC M-7050 Power amp and PL-10 pre amps as they have some issues as well. The first tech fixed some problems, I thought, but it's still not right. The 7050 is a beast!
Glenn
Next I'll bring him my JVC M-7050 Power amp and PL-10 pre amps as they have some issues as well. The first tech fixed some problems, I thought, but it's still not right. The 7050 is a beast!
Glenn
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