Marantz SR7500 Buzz/hum

[moosefuel]

Hi everyone, I acquired a Marantz SR7500 for not too expensive, I'm told that they are great sounding amps and have analog circuits for some inputs. Pretty cool.

Once mine turns on, it has a noticeable buzz which increases when I turn the volume knob. It doesn't seem to matter which input I set it to, although the timbre of the buzz changes a little between the different inputs. I have nothing plugged in at the moment, just the speakers. The buzz is present in the headphone output, too.

I'm not too bad with a soldering iron, so I opened up the amp. I can identify the different boards somewhat, but I don't really have any idea which is causing the buzz or what to do about it. I don't see any obviously bad capacitors, and I don't want to just start messing with stuff without any idea of what's causing it. Has anyone solved a similar problem? What should I try?

Yes I've tried plugging it in to another outlet, and another house for that matter.

Thanks!

 

[TLS Guy]

Hi everyone, I acquired a Marantz SR7500 for not too expensive, I'm told that they are great sounding amps and have analog circuits for some inputs. Pretty cool.

Once mine turns on, it has a noticeable buzz which increases when I turn the volume knob. It doesn't seem to matter which input I set it to, although the timbre of the buzz changes a little between the different inputs. I have nothing plugged in at the moment, just the speakers. The buzz is present in the headphone output, too.

I'm not too bad with a soldering iron, so I opened up the amp. I can identify the different boards somewhat, but I don't really have any idea which is causing the buzz or what to do about it. I don't see any obviously bad capacitors, and I don't want to just start messing with stuff without any idea of what's causing it. Has anyone solved a similar problem? What should I try?

Yes I've tried plugging it in to another outlet, and another house for that matter.

Thanks!

You have bought a dud most likely. If it hums with only speakers and AC connected the unit is likely a recycling job. I just had and AVP do exactly that and then it had a spectacular failure that could have done a lot of damage. You are not going to service that receiver. Components are now mounted by robot surface with hot air soldering.

That is a 20 year old receiver and so there will be no parts. My AVP was only five years old, but Marantz had no parts available so it was marked for death.

Buying an AVR that old was very unwise.

 

[moosefuel]

Buying an AVR that old was very unwise.

It's too bad they don't make these to last. I have other computers/car/etc. which are 30+ years old and still work fine. Granted, I've done maintenance over the years.

It's not the worst decision I've ever made, but if I can't get any better answers, I think you're right, it's off to the recycler.

 

[j_garcia]

7500 is semi-old, but was a good unit. I had m 8300 for over 10 years before it started to have some minor issues, but it still worked. I have the same AVP currently that TLS had before, and the warranty is up soon, so I could be looking before long also.

 

[TLS Guy]

It's too bad they don't make these to last. I have other computers/car/etc. which are 30+ years old and still work fine. Granted, I've done maintenance over the years.

It's not the worst decision I've ever made, but if I can't get any better answers, I think you're right, it's off to the recycler.

I think the biggest issue is the huge part count, which increases the risk of failure. These units rise in complexity year by year. They use standard components. If they used auto grade, let alone aircraft grade the costs would go through the roof. I dio have two AVPS in daily use that have been in regular use for ten years. I think it is fair to say that it is reasonable to consider these units on borrowed time after 14 to 15 years.

So, it is not like it used to be. I have units up to 60 years old in regular use, and working fine. But these are simpler analog units.

So, I would look for something newer or even new.

 

[Eppie]

The complexity of these AVRs make them very difficult to service. It could be as simple as a cold solder joint somewhere but tracing the noise is the challenge. You need either a very sensitive audio probe or an oscilloscope to trace the audio path backwards. If the buzz increases with the volume control, that indicates that the problem is not in the amp section but in the pre-amp or in the digital processing sections. If you don't have the diagnostic equipment then the members are correct and it is likely destined for recycling.

 

[moosefuel]

destined for recycling.

Sad to hear, but thank you. I'll have one last look at it and then get rid of it. Only thing worse than wasting $50 on it would be to waste all my time and $50.

 

[j_garcia]

The complexity of these AVRs make them very difficult to service. It could be as simple as a cold solder joint somewhere but tracing the noise is the challenge. You need either a very sensitive audio probe or an oscilloscope to trace the audio path backwards. If the buzz increases with the volume control, that indicates that the problem is not in the amp section but in the pre-amp or in the digital processing sections. If you don't have the diagnostic equipment then the members are correct and it is likely destined for recycling.

At which point a service center would replace the entire board. A friend started buying certain laptops with bad motherboards like this that he is familiar with off ebay and he has been reflowing solder on the boards. That seems to result in a large percentage of them starting to work again, but it is just a matter of time until something else fails IMO.

 

[moosefuel]

reflowing solder on the boards.

Actually that's a really good idea. I've heard of some electronics working for years after being baked in an oven at the right temperature. I might give it a try.

 

[j_garcia]

For $50, is worth a shot if you're going to boat anchor it anyway.

 

[lovinthehd]

Buying a 20 year old avr that's mostly analog probably not a bad bet, but still taking your chances with age. That you bought it because it is said to be by some of the great unwashed that is "great sounding" is not a good buying basis.

 

[moosefuel]

some of the great unwashed that is "great sounding" is not a good buying basis.

Thank you for pointing out the obvious

 

[lovinthehd]

Thank you for pointing out the obvious

Then why ask here if you already have a good handle on it?

 

[TLS Guy]

Actually that's a really good idea. I've heard of some electronics working for years after being baked in an oven at the right temperature. I might give it a try.

Have a CO2 fire extinguisher handy. I think heating that in a oven and then switching it on, is unwise and unsafe. The worst outcome is that it might work initially and then burn your house down. I have looked into this, and it occasionally gets devices running for a brief period of time.

I looked at eBay prices and these units go for rock bottom junk prices in the $100 to $150 range. In my view they are not worth the shipping. That unit has no HDMI connectivity so as a video device it is virtually useless in this day and age. You would need a TV with analog video inputs to even set it up.

Carefully buying vintage selected audio devices can have merit, if you know what you are doing, but not AV devices. My advice is clear, dump that boat anchor.