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What is this noise? Hum, Hiss or something else?


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My vintage Accuphase integrated amp starting to develop weird noise on phono (MM & MC) section (all other inputs are okay) which drives me nuts.

I do not think that it is hiss or hum but constant rapid tapping noise (like shoot machine gun).

 

Here is the sound clip that I recorded using my phone.

https://voca.ro/1fBTrNAX6N0n

 

This is only on left channel and right channel is fine.

 

Does anyone know what this noise is called? And what is the common cause of this?

 

Thank you.....

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Power supply looks common for MM L&R channels. No electrolytics in MM audio path. Try the freeze spray on the dual FET, the 9 pin (SIP) opamp and the 2 transistors. Post some pix of component side

You could poke around with a wooden or a plastic stick while the power is on with speaker connected and listen for any pops to insulate any bad connections/solder joints. Keep your fingers out of

Those electrolytic caps in there look like ones that would vent from the bottom rather than the top, and It's usually top venting caps that will show bulging if they do.   Edit: I think.

No idea, and I agree It's weird! never heard anything like that before 🤔

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Sounds like maybe transistor breakdown, possibly even capacitor breakdown, or even a bad solder joint. Try applying hot air from a hair dryer, or cool air from a low flow of compressed air, or both alternately to try and localise the component causing the problem.

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2 minutes ago, bob_m_54 said:

Sounds like maybe transistor breakdown, possibly even capacitor breakdown, or even a bad solder joint. Try applying hot air from a hair dryer, or cool air from a low flow of compressed air, or both alternately to try and localise the component causing the problem.

 

Thank you for suggestion. I never heard about applying hot air onto components or PCB board to diagnose problem. I guess that it is to find cold solder joint?

 

Where do you suggest applying hot air onto? And, what do we look for when we applying hot air from hair dryer?

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12 minutes ago, Spider27 said:

 

Thank you for suggestion. I never heard about applying hot air onto components or PCB board to diagnose problem. I guess that it is to find cold solder joint?

 

Where do you suggest applying hot air onto? And, what do we look for when we applying hot air from hair dryer?

It works on components too.. some components become more heat sensitive as they get older and are nearing failure. So you give it a bit of shock treatment, by alternating hot and cold to see which components may be suffering this way. But you need to try and localise the heating and cool, which isn't easy to do without proper gear. You can get cans of freeze spray that can be very effective for this. Just using a tiny short squirt on each component at a time. But freeze spray is pretty expensive.

 

As for solder joints, what it does is expand and contract the metal, which causes the intermittency to happen. Tapping with a non-conductive object, on the component can also find faulty joints.

 

A cold solder joint just means a solder joint where the solder didn't melt properly so it could flow and wett the joint properly. Cold joint, dry joint fractured joint are all very similar, but different causes.

 

If the equipment is mains powered, DON'T DO THIS UNLESS YOU ARE PROFICIENT IN WORKING WITH ELECTRICAL EQUIPMENT WITH THE POWER ON..................... If you touch the wrong thing with your pinky, you could end up dead.  

Edited by bob_m_54
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What I used to mainly do was give the equipment a general warm up with a hot air gun on low, in different areas of the circuit board, then spot cool different components with a low flow of compressed air through a plastic tube, to keep it localised. Freeze spray works better, but too expensive to keep using freeze spray when you are doing it for a living.

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6 minutes ago, bob_m_54 said:

What I used to mainly do was give the equipment a general warm up with a hot air gun on low, in different areas of the circuit board, then spot cool different components with a low flow of compressed air through a plastic tube, to keep it localised. Freeze spray works better, but too expensive to keep using freeze spray when you are doing it for a living.

 

It makes sense because the problem starts happening after 20~30 mins playing which means that it warmed up. Thank you again for the tip and I will seriously consider this option using freeze spray and also be very careful if I do this. 😊

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Just be very very careful... Stay away from the mains powered areas... don't use a lead pencil if you try the tapping method. The graphite in the lead pencil is conductive, so could be dangerous if you inadvertantly probe around mains power...

 

Be careful, I don't want to read about you in the papers..... LOL

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Can buy the freeze spray from jaycar, have a can in the cupboard for this use on rare occasions.

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As it has recently started and is only present after the unit warms up I'm going to suggest a visit to a good tech, unless you are competent with such things yourself. It's highly likely that some soldering and possible component replacement will be needed.

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12 minutes ago, GregWormald said:

As it has recently started and is only present after the unit warms up I'm going to suggest a visit to a good tech, unless you are competent with such things yourself. It's highly likely that some soldering and possible component replacement will be needed.

 

Thank you. Yes, I am on the same picture. I will have a closer look at inside to see if I can fix it myself but if not, then will just take it to local technician.

I learned a hard lesson messing with old amp and made it worse and it eventually costs a lot more than it supposed to be if I took it straight to tech before messing things up. 

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Problem appears to be with the MM stage since both MM&MC affected. Post 2-3 hi res pix of solder side of MM board/area, hopefully dry solder joints will stand out.  Use the freeze spray, probably only 3-5 transistors per MM channel. Allow 20-30 seconds for transistor to recover before moving to next. What model number? Service manual may be available of hifiengine or...

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4 minutes ago, Ihearmusic said:

Sounds like Motorboating to me and and might indicate local B+ decoupling capacitors are on the way out.

Even better, maybe a $1- cap and a bit of diy...

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4 minutes ago, Ihearmusic said:

Sounds like Motorboating to me and and might indicate local B+ decoupling capacitors are on the way out.

 

 

Yes, it might be motorboating. Thank you..

 

Re: local B+ decoupling capacitors, if we have schematics, can we identify which one is B+ decoupling one?

 

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5 minutes ago, mbz said:

Problem appears to be with the MM stage since both MM&MC affected. Post 2-3 hi res pix of solder side of MM board/area, hopefully dry solder joints will stand out.  Use the freeze spray, probably only 3-5 transistors per MM channel. Allow 20-30 seconds for transistor to recover before moving to next. What model number? Service manual may be available of hifiengine or...

 

It is E-203 model and schematics is available and attached here.

hfe_accuphase_e-203_schematic.pdf

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Just now, Spider27 said:

 

 

Yes, it might be motorboating. Thank you..

 

Re: local B+ decoupling capacitors, if we have schematics, can we identify which one is B+ decoupling one?

 

Yes, we should be able to highlight them. You might find  that some of the caps will be bulging a bit, that is a good indication of them on the way out. With vintage gear it is very beneficial to replace all caps. 

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2 minutes ago, Spider27 said:

 

It is E-203 model and schematics is available and attached here.

hfe_accuphase_e-203_schematic.pdf 1.09 MB · 1 download

Thanks

13 minutes ago, Spider27 said:

 

 

Yes, it might be motorboating. Thank you..

 

Re: local B+ decoupling capacitors, if we have schematics, can we identify which one is B+ decoupling one?

 

C27, C28 for starters. ( I am guessing a bit as I normally do tube stuff)

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Power supply looks common for MM L&R channels. No electrolytics in MM audio path. Try the freeze spray on the dual FET, the 9 pin (SIP) opamp and the 2 transistors. Post some pix of component side to check for stressed caps.

image.png.0172dbbc580472bfca68236fbe247204.png

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16 hours ago, Ihearmusic said:

Sounds like Motorboating to me and and might indicate local B+ decoupling capacitors are on the way out.

Had a thought about that too.. but it's a bit too irregular in the way it manifests.. Motorboating usually sounds, well a bit like a motorboat.. LOL where the pops are regular... this sounds more like either transistor breakdown, or a very fine fracture in a solder joint.

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2 hours ago, bob_m_54 said:

Had a thought about that too.. but it's a bit too irregular in the way it manifests.. Motorboating usually sounds, well a bit like a motorboat.. LOL where the pops are regular... this sounds more like either transistor breakdown, or a very fine fracture in a solder joint.

 

Yep, I actually sent the sound file to a technician and he says the same thing. It is irregular pattern so might not be motorboating but it sounds like noise caused by interference from wireless electronic devices around the area. In my room, my phone is 1.5m away and no router or modem so it must be something else. And, the noise starts appearing after amp is warmed up (20~30 mins after).

 

 

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Here is the inside shot of the main board. I checked visually and no bulging caps or anything out of ordinary. I might check underneath to see if there is any dry joint.

 

 

IMG_8874.jpg

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I thought about that, but in one channel only sounds odd.

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Those electrolytic caps in there look like ones that would vent from the bottom rather than the top, and It's usually top venting caps that will show bulging if they do.

 

Edit: I think.

Not too sure on the smaller electrolytic ones at the rear of the board..

Edited by muon*
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On 23/06/2021 at 2:47 PM, bob_m_54 said:

DON'T DO THIS UNLESS YOU ARE PROFICIENT IN WORKING WITH ELECTRICAL EQUIPMENT WITH THE POWER ON

The single most important thing said on this thread.

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Thanks for the pix, I don't see anything sinister (bulging caps, signs of heat stress, charred components...). A pix of the solder side may be helpful, is the base plate removeable? Check solder connections around heat sink mounted transistors. Been some instances in vintage yamaha where such transistors partly "unsolder" themselves due to the extra heat.

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On 24/06/2021 at 7:20 PM, mbz said:

Thanks for the pix, I don't see anything sinister (bulging caps, signs of heat stress, charred components...). A pix of the solder side may be helpful, is the base plate removeable? Check solder connections around heat sink mounted transistors. Been some instances in vintage yamaha where such transistors partly "unsolder" themselves due to the extra heat.

 

Here is the back side of the main board.

 

 

 

Solder Side.jpeg

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You could poke around with a wooden or a plastic stick while the power is on with speaker connected and listen for any pops to insulate any bad connections/solder joints.

Keep your fingers out of the unit of course while power is plugged in.

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Posted (edited)

I found 3~4 suspicious solder joints so gave fresh solder on those and put it back.

 

Here are a few additional things that I found.

 

+ After re-solder a few joints, the noise on left channel appear after 45~60 mins instead of 25~30 mins. 

And, noise appear a bit less frequent but still there.

 

+ Occasionally, left channel on Phono input gets less output than right channel.

 

+ When I check the main caps on the board using ESR meter, they seem all within range but one or two are noticeably less value (may be too good). 1000 uf 35v cap suppose to be less than 0.07 but found that 0.01 value on one or two caps among C27~C30.   I should take a measure by taking caps completely out but just checked when they are still in the board.

Edited by Spider27
typo
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6 minutes ago, Ihearmusic said:

You could poke around with a wooden or a plastic stick while the power is on with speaker connected and listen for any pops to insulate any bad connections/solder joints.

Keep your fingers out of the unit of course while power is plugged in.

 

Great tip. Thank you. I forgot to do that when I checked solder joints earlier today. Will using wooden chopstick to gently tap to see if it helps.

 

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Solder side pic resolution is not great, maybe focus on MM stage only, ie,

image.png.153be376cb6deda17cb26bbc140eefc1.png

 

Also, you could search "dry solder joints" will give you some pix to get an idea of what to look for. I'd be suspicious of any annualized rings (or part of) in the MM stage.

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17 hours ago, Spider27 said:

I found 3~4 suspicious solder joints so gave fresh solder on those and put it back.

 

Here are a few additional things that I found.

 

+ After re-solder a few joints, the noise on left channel appear after 45~60 mins instead of 25~30 mins. 

And, noise appear a bit less frequent but still there.

 

+ Occasionally, left channel on Phono input gets less output than right channel.

 

+ When I check the main caps on the board using ESR meter, they seem all within range but one or two are noticeably less value (may be too good). 1000 uf 35v cap suppose to be less than 0.07 but found that 0.01 value on one or two caps among C27~C30.   I should take a measure by taking caps completely out but just checked when they are still in the board.

A lower ESR (Effective Series Resistance) is better.. High ESR means the cap is drying out and not working properly.

 

Some of the electro caps in your pic look like they have a bit of outer plastic film shrinkage. This is a good indicator of caps that have been in a hot environment for a long time, and therefore could be suffering from electrolyte drying out. Which would show as a higher ESR. No need to take caps out to measure ESR..

 

Pay special attention to the solder joints in areas where the board looks a bit darker due to overheating. Any joints that look frosty, or where the component lead shows corrosion down through the joint are suspect. Poor joints may not be visible just using your eye, and may still be difficult to see using a magnifying glass.

 

One thing I did notice, but doubt it is related to your problem.. The mark on the top of Q29 in your pic. Is that a crack, or is it just a shadow from the mould seam (ridge)?

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On 23/06/2021 at 7:53 PM, mbz said:

Power supply looks common for MM L&R channels. No electrolytics in MM audio path. Try the freeze spray on the dual FET, the 9 pin (SIP) opamp and the 2 transistors. Post some pix of component side to check for stressed caps.

 

 

Dumb question.. May I ask where is this dual FET highlighted with arrow? I found the rest of highlighted one but could not locate this one somehow. Thank you...

 

 

image.png.0172dbbc580472bfca68236fbe247204.png

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Hard to replicate the issue once I take the amp out of rack and remove the bottom cover. 

 

I was playing 4 hours straight and the issue does not come up once I put the amp upside down and remove the bottom cover. (The reason for upside down is because all of main PCBs are mounted downwards unlike other amps - well known configuration for Accuphase). I believe that better ventilation prevent it happening.

 

Once I put the bottom cover on and play 30mins to 1 hour hard then it appears again but when I take the bottom cover off, then it soon disappear so very hard to diagnose with freeze spray or tapping with wooden sticks. 😳

 

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Have you tried with bottom cover on and amp upside down?

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2 hours ago, mbz said:

Have you tried with bottom cover on and amp upside down?

 

Yep, I am putting the cover on so I can get the replicate the issue. As soon as I lift the cover then it slowly goes away and appear it random but much less frequently so I put the cover back on again waiting for the issue comes back and repeat the process.

 

I applied freeze spray just a bit on those highlighted components.     Two caps (C27, C28) and 9 pin opamp do not make any changes.

 

Dual FET (Q21) and Two Transistors (Q23 & Q25) do make some difference when I apply Freeze spray. Not exactly sure which one or ones are heat sensitive because it goes away soon after I remove the cover.

 

I noticed that Q23 & Q25 are mounted on small square heatsink without any thermal paste. Would it help if I apply tiny bit of thermal paste between heatsink and transistors? Or it would not make any difference?

 

 

 

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23 hours ago, Spider27 said:

Hard to replicate the issue once I take the amp out of rack and remove the bottom cover. 

 

I was playing 4 hours straight and the issue does not come up once I put the amp upside down and remove the bottom cover. (The reason for upside down is because all of main PCBs are mounted downwards unlike other amps - well known configuration for Accuphase). I believe that better ventilation prevent it happening.

 

Once I put the bottom cover on and play 30mins to 1 hour hard then it appears again but when I take the bottom cover off, then it soon disappear so very hard to diagnose with freeze spray or tapping with wooden sticks. 😳

 

That's why you use hot air from a hair dryer, or hot air gun, to induce the problem more quickly. Once you have the area hot enough to induce the fault, then spot spray the different components, and see if there is any change. if there is a noticeable change, those components are suspect.

 

What I would do firstly though, is using your insulated chopstick (I used to use a plastic chopstick myself LOL), tap all the components in the area, one by one, and see if there is any noise from them. That would point to a bad solder joint as the problem.

 

If that doesn't work, then try the heating/cooling method, which will show up bad components and bad solder joints.

 

Did you see my comment about the transistor Q29 in my previous post? It's not the cause of your problem, if it is confined to one channel, as it's part of the 22V P/S circuit, but it just looks a  bit suspect in the picture.

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1 hour ago, bob_m_54 said:

That's why you use hot air from a hair dryer, or hot air gun, to induce the problem more quickly. Once you have the area hot enough to induce the fault, then spot spray the different components, and see if there is any change. if there is a noticeable change, those components are suspect.

 

What I would do firstly though, is using your insulated chopstick (I used to use a plastic chopstick myself LOL), tap all the components in the area, one by one, and see if there is any noise from them. That would point to a bad solder joint as the problem.

 

If that doesn't work, then try the heating/cooling method, which will show up bad components and bad solder joints.

 

Did you see my comment about the transistor Q29 in my previous post? It's not the cause of your problem, if it is confined to one channel, as it's part of the 22V P/S circuit, but it just looks a  bit suspect in the picture.

 

Thank you and great idea using hot air gun.   

 

I did chopstick test on all of components on the main board yesterday and no noise from any of them.

Yes, Q29 is fine when I check the solder joint and also did chopstick test.

 

I will do further testing and report if there is any noticeable findings. 😊

 

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