Vintage jvc ax-4 amplifier
cedric_06
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Hello, I have been the happy owner of a JVC A-X4 amplifier for a few years now (5 years) connected to my computer constantly for a minimum of 8 hours a day, and it's starting to show signs of fatigue. Let me explain: when I turn it on, nothing happens, but after a certain period of time, the amp seems to kick in with a loud thump in my speakers that almost disassemblies them, then it crackles, and as a result, I have to disable the equalizer in order for the sound to go back to normal. However, this bothers me because disabling the equalizer makes the sound linear, and I prefer to personalize the music I listen to.
Anyway, I hope I was clear enough and that you can help me.
Thank you.
Anyway, I hope I was clear enough and that you can help me.
Thank you.
7 réponses
Hi,
In your opinion, could it be a problem with the equalizer controls?
Do you turn it on with the equalizers disabled?
When you say nothing happens, is that before the relay clicks?
Have you opened it?
Cleaned the controls?
I would recommend DeoxIT Faderlube F-5 to clean/lubricate the faders (slider potentiometers)
But the problem might not stop there.
The first thing I do when I receive a device that’s a bit old is a complete cleaning.
When I say complete, I mean complete.
The only thing that doesn’t end up being rinsed thoroughly after cleaning with certain products is the transformer.
Do you have a multimeter?
Photos of the inside would be welcome.
PS: Service Manual (EN)
In your opinion, could it be a problem with the equalizer controls?
Do you turn it on with the equalizers disabled?
When you say nothing happens, is that before the relay clicks?
Have you opened it?
Cleaned the controls?
I would recommend DeoxIT Faderlube F-5 to clean/lubricate the faders (slider potentiometers)
But the problem might not stop there.
The first thing I do when I receive a device that’s a bit old is a complete cleaning.
When I say complete, I mean complete.
The only thing that doesn’t end up being rinsed thoroughly after cleaning with certain products is the transformer.
Do you have a multimeter?
Photos of the inside would be welcome.
PS: Service Manual (EN)
Yes, there's a click that happens as if there's a bad connection, then the sound comes back but it's crackling, so I have to disable the equalizer. But otherwise, without the equalizer, it doesn't cut out even with prolonged high volume. No, I don't have a multimeter, and it was full of dust which I cleaned off with a brush, but under the dust, I noticed a suspicious stain on a rectangular component (it's not a transistor), and there are no swollen or exploded capacitors. As for the photos, I'll try to get them done as soon as possible.
The click is normal. It's the delay relay at startup that prevents a "thump" in the speakers, if something isn't running (smoothly) that could damage them. For example... destroying the speakers, but I don't think they would be at much risk the first time.
Now for the failure, we should look elsewhere, but I don't think I can help you. I don't know anything about electronics.
Now for the failure, we should look elsewhere, but I don't think I can help you. I don't know anything about electronics.
The equalizer circuit is in perfect condition, everything is very clean, no corrosion on the solder joints except for this stain that looks sticky on this 8-pin component in a line. The component is green and it says "super A" on it.
For the switches, you would be better off using DeoxIT D-5
It is also used in rotary potentiometers, before lubrication with Faderlube.
You can clean the solder side with acetone and a toothbrush, finishing with window cleaner and water.
Window cleaner and water may be sufficient for the side of the components, just a quick rinse.
Yes, a brush helps.
It is also used in rotary potentiometers, before lubrication with Faderlube.
You can clean the solder side with acetone and a toothbrush, finishing with window cleaner and water.
Window cleaner and water may be sufficient for the side of the components, just a quick rinse.
Yes, a brush helps.
Hello, still no photos but I have new information to give you, probably important:
the two large electrolytic capacitors in the middle have leaked
is it serious?
their references are 56v8700µF
I didn't see them directly because they leaked from underneath and on top, they're fine, not even bulging.
the two large electrolytic capacitors in the middle have leaked
is it serious?
their references are 56v8700µF
I didn't see them directly because they leaked from underneath and on top, they're fine, not even bulging.
Check for any corroded components
Some manufacturers (in the 80s) used glue that has been found to become corrosive after X years.
https://www.audiokarma.org/forums/index.php?threads/au-717-deadly-glue.63404/
Some manufacturers (in the 80s) used glue that has been found to become corrosive after X years.
https://www.audiokarma.org/forums/index.php?threads/au-717-deadly-glue.63404/
Hi,
No, it could damage them in the short or long term.
CAIG Laboratories, Inc. has a whole range of "DeoxIT" products specifically for that.
DeoxIT D5, DeoxIT D100 (deoxidizing cleaners)
DeoxIT Fader (Faderlube) F5, F100 (cleaning/lubricating)
DeoxIT Gold ... (protectors)
DeoxIT Shield ... (protectors)
...
No, it could damage them in the short or long term.
CAIG Laboratories, Inc. has a whole range of "DeoxIT" products specifically for that.
DeoxIT D5, DeoxIT D100 (deoxidizing cleaners)
DeoxIT Fader (Faderlube) F5, F100 (cleaning/lubricating)
DeoxIT Gold ... (protectors)
DeoxIT Shield ... (protectors)
...