Hi.
I have an old HI-FI system for more than 10 years and its cooling
fan(40X40X10/12v/2 wires/2 rolling bearing)didn't have a noticeable noise before
I even didn't know that it exist.
During the past year the fan made too much noise.
When i turn the hi-fi on,the fan is off,after couple of minutes it starts
to spin,but quietly,but as the minutes passes,the noises gradually
get louder and stay louder,while very annoying.
The volume of the speakers are just medium.
I bought a new fan(hydraulic one),as i assumed that the bearing are worn,but
the new fan makes even worse noises.
Maybe i need to buy a better fan than i bought,but my questions are:
Can it be other failure in the pcb components/sensors?as the fan is turn-on and gradually
rise up to the highest spin,permanent,while i only use medium volume?
There isn't any dust on the pcb,the fan is connected well to the chassis.

Thanks.

 

Small cooling fans often have a noise rating.
You want one with a low dB value.

What type of fan is it?

 

Is that size 40x40x10? If so what units?
Is it possible to use a PC enclosure venting fan, they run exceedingly quiet.

 

Small cooling fans often have a noise rating.
You want one with a low dB value.

What type of fan is it?

Is that size 40x40x10? If so what units?
Is it possible to use a PC enclosure venting fan, they run exceedingly quiet.

As i mentioned in my post:
The old one is 40X40X10/12v/2 wires/with 2 rolling bearing.
But my concern is not the fan as it is not a problem to replace it
with low dB one.
My question was:if a kind of a failure in the pcb component can cause the fan to behave like that.
As i mention before,the behavior is like that:
When i turn-on the hi-fi ,the fan is off,after couple of minutes it starts
to spin quietly,but as the minutes passes,the noises gradually
get louder and stay louder,while the volume of the speakers are just at medium level.When i turn-off the hi-fi,the fan is keeping make a loud noises,like it is spin at maximum and it doesn't shut-off until i pulls out the plug from the socket.

 

As i mentioned in my post:
The old one is 40X40X10/12v/2 wires/with 2 rolling bearing.

40 What??

 

As i mentioned in my post:
The old one is 40X40X10/12v/2 wires/with 2 rolling bearing.
But my concern is not the fan as it is not a problem to replace it
with low dB one.
My question was:if a kind of a failure in the pcb component can cause the fan to behave like that.
As i mention before,the behavior is like that:
When i turn-on the hi-fi ,the fan is off,after couple of minutes it starts
to spin quietly,but as the minutes passes,the noises gradually
get louder and stay louder,while the volume of the speakers are just at medium level.When i turn-off the hi-fi,the fan is keeping make a loud noises,like it is spin at maximum and it doesn't shut-off until i pulls out the plug from the socket.

The heat related speed control circuit seems to be fine judging from your description of events. The hi-fi warms up and circuit sends fan power to cool, heat continues to rise, etc ...

Cheap junk fans with cheap junk bearings are usually the culprit. Replace with a better brand.
https://www.mouser.com/c/thermal-management/fans-blowers/fans/dc-fans/?q=fan 40x40x10&bearing type=Ball&depth=10 mm&noise=14 dBA~~16.5 dBA|~20 dBA|~21 dBA~~21.5 dBA|~25 dBA&operating supply voltage=12 VDC&width=40 mm&instock=y&rp=thermal-management/fans-blowers/fans/dc-fans|~Noise

 

Though this may not be a useful contribution, I recall an incident with a friend and a rented moving truck. It was summer and the truck had AC. But when you ran the AC fan the fan motor bushing noise was horrible. He ended up not hearing a police siren. He got ticketed. In his defense he had the rental company sign an affidavit saying that the AC "BELT" was slipping. He was forgiven because he could not hear the siren. However, there are people who mistake one noise for another. In the case of a 10 year old fan I'd favor believing it's old dry bushings. Bushings are not the same as bearings. Nevertheless, if the fan is noisy see if you can purchase the same thing. After all, it was quiet for 10 years. A new fan will likely be good for that long at least.

As for exactly what kind of noise it is - I doubt it's anything electronic. Most likely the noise of the fan itself. Even fan blades can be noisy. Have you ever seen fan blades with what look like saw teeth on the trailing edge? That's to reduce the noise of turbulent air. If you look at modern jet aircraft you see the same sawtooth on the output of the jet engine. Again, that's to reduce noise. The local Air Force does NOT have those teeth and HECK! Do they ROAR over my house. One particular rocket jockey loves going low and hot. He comes so fast and is gone so quickly I don't have time to grab my camera and run out and capture him. One of these days I'll be in the right place and catch him. When I do - it will go on YouTube and y'all will get a link to the video. I gotta say it's impressive as all get-go.

 

The heat related speed control circuit seems to be fine judging from your description of events. The hi-fi warms up and circuit sends fan power to cool, heat continues to rise, etc ...

Cheap junk fans with cheap junk bearings are usually the culprit. Replace with a better brand.
https://www.mouser.com/c/thermal-management/fans-blowers/fans/dc-fans/?q=fan 40x40x10&bearing type=Ball&depth=10 mm&noise=14 dBA~~16.5 dBA|~20 dBA|~21 dBA~~21.5 dBA|~25 dBA&operating supply voltage=12 VDC&width=40 mm&instock=y&rp=thermal-management/fans-blowers/fans/dc-fans|~Noise

But why when i turn-off the hi-fi,the fan keeps spinning at the highest rpm and doesn't stop or at least decrease its rpm for hours,unless i pulls out the plug from the socket?doesn't it indicate some kind of a fault?

40 What??

40mmX40mmX10mm

Though this may not be a useful contribution, I recall an incident with a friend and a rented moving truck. It was summer and the truck had AC. But when you ran the AC fan the fan motor bushing noise was horrible. He ended up not hearing a police siren. He got ticketed. In his defense he had the rental company sign an affidavit saying that the AC "BELT" was slipping. He was forgiven because he could not hear the siren. However, there are people who mistake one noise for another. In the case of a 10 year old fan I'd favor believing it's old dry bushings. Bushings are not the same as bearings. Nevertheless, if the fan is noisy see if you can purchase the same thing. After all, it was quiet for 10 years. A new fan will likely be good for that long at least.

As for exactly what kind of noise it is - I doubt it's anything electronic. Most likely the noise of the fan itself. Even fan blades can be noisy. Have you ever seen fan blades with what look like saw teeth on the trailing edge? That's to reduce the noise of turbulent air. If you look at modern jet aircraft you see the same sawtooth on the output of the jet engine. Again, that's to reduce noise. The local Air Force does NOT have those teeth and HECK! Do they ROAR over my house. One particular rocket jockey loves going low and hot. He comes so fast and is gone so quickly I don't have time to grab my camera and run out and capture him. One of these days I'll be in the right place and catch him. When I do - it will go on YouTube and y'all will get a link to the video. I gotta say it's impressive as all get-go.

I had opened the old one,it has 2 bearing(it is not sleeve type)and the noise is from the fan,but it is annoying only when it rise to the highest spin.
Again my concern is not the fan,as it is not a problem to replace it.My concern is to find out if there is any failure in the pcb component that making the fan to act at the behavior that i described before.

 

My concern is to find out if there is any failure in the pcb component that making the fan to act at the behavior that i described before.

I doubt it. Can't say for sure, but I really don't think it's anything electronic. One thing you can do to test the fan for noise is power it from a stand alone power source, one that puts out the max voltage the fan is rated for. Run the fan up. See if it still makes noise. If it's 12 volts - you did say it was - get some small jumpers and take the fan out to your car. Tap the fan on to the battery terminals. Spin it up at full speed. If it's noisy then you have your definitive answer

 

That fan was originally designed for 1U rack-mount equipment, and got picked up by the CPU cooler manufacturers. All of the fans I used in that size were screamers, although the 10 mm thick ones were the quietest of the bunch.

How loud is the old fan when connected directly to a 12 V supply, outside of the enclosure? Also, when cold, does it ramp up to full speed slowly, or go straight to max blast?

ak

 

But why when i turn-off the hi-fi,the fan keeps spinning at the highest rpm and doesn't stop or at least decrease its rpm for hours,unless i pulls out the plug from the socket?doesn't it indicate some kind of a fault?

40mmX40mmX10mm

I had opened the old one,it has 2 bearing(it is not sleeve type)and the noise is from the fan,but it is annoying only when it rise to the highest spin.
Again my concern is not the fan,as it is not a problem to replace it.My concern is to find out if there is any failure in the pcb component that making the fan to act at the behavior that i described before.

The fault is your fan. That is the noise source, replace it ASAP.

One possible reason for the current fan behaviour.
The circuit has likely gone into protective cooling mode, always on mode, when it detects poor cooling (slower air flow because of bad bearing that also cause noise) when the power to the fan was increased in response to increasing temperatures with little or no cooling response increase. Just a guess of a possible circuit protection mode that a new fan could fix.

 

Might be an idea to measure the temperature before switching on and then for the next few minutes, as the fan speeds up.
Is the temperature increasing significantly?
If not, its likely to be the fan control circuit causing the fan to run too fast.
If it is, then try to identify what is getting hot.
Then try to work out why its getting hot.....

 

The very first suggestion I offer is to lubricate the bearings of that fan motor. Bearing vibration can cause problems that do not seem related, but are caused by the vibration affecting microphonic components. And ball bearings can certainly lead to vibration when they approach failure.

 

The very first suggestion I offer is to lubricate the bearings of that fan motor. Bearing vibration can cause problems that do not seem related, but are caused by the vibration affecting microphonic components. And ball bearings can certainly lead to vibration when they approach failure.

When those fan bearing are so worn as to cause the type of vibration likely heard here, lubrication (we've all tried it) is a worn out race/bearing space filler, noise damper and abrasive (bearing dust and grease) mixture that will likely accelerate total fan failure.
Per my equipment life extension protocol, any cooling fan(s) past 10 years is automatically replaced in a major power related repair even if it seems good.

 

The very first suggestion I offer is to lubricate the bearings of that fan motor. Bearing vibration can cause problems that do not seem related, but are caused by the vibration affecting microphonic components. And ball bearings can certainly lead to vibration when they approach failure.

In past endeavors to do just this I've found some fans were able to be opened but with much bother. Others just couldn't be opened without damaging them. Using any kind of lubricant on ball bearings is seldom recommended. Lubrication collects dust and impacts it into the bearing races. Eventually the bearing will seize up. I've had sealed motor bearings freeze up before. Popping the dust cover off (which damages it) will allow a solvent to clean the bearings and eventually free them up but they never perform the way they were originally designed to. They're noisier, they don't run smooth, and they just get dirty quicker. Even if you put the dust cover back on.

 

The bearing are very small(5mm) and i don't think it can be opened(without damage it).Btw,i had tried to drop on them drops of low viscosity oil before,but with no improved.
As Tonyr1084 and nsaspook suggested,the bearing/races are probably damaged and it can't be repaired or make them quite again.

That fan was originally designed for 1U rack-mount equipment, and got picked up by the CPU cooler manufacturers. All of the fans I used in that size were screamers, although the 10 mm thick ones were the quietest of the bunch.

How loud is the old fan when connected directly to a 12 V supply, outside of the enclosure? Also, when cold, does it ramp up to full speed slowly, or go straight to max blast?

ak

When cold,it starts spinning after few minutes and ramp up to full speed slowly.When connected directly to 12V supply outside it sound,i think,less loud than when it is inside the hi-fi at full speed.

The fault is your fan. That is the noise source, replace it ASAP.

One possible reason for the current fan behaviour.
The circuit has likely gone into protective cooling mode, always on mode, when it detects poor cooling (slower air flow because of bad bearing that also cause noise) when the power to the fan was increased in response to increasing temperatures with little or no cooling response increase. Just a guess of a possible circuit protection mode that a new fan could fix.

Might be an idea to measure the temperature before switching on and then for the next few minutes, as the fan speeds up.
Is the temperature increasing significantly?
If not, its likely to be the fan control circuit causing the fan to run too fast.
If it is, then try to identify what is getting hot.
Then try to work out why its getting hot.....

According to the measuring temperature suggested and the protective cooling mode action,i thing that i better look for a good quite new fan,replace it and hope for good.
Thanks for everyone for your help.

 

Often it is possible to lubricate bearings without disassembling a fan. But sometimes it is not, in which case replacement is needed. Mostly such small fans are a pressed together assembly, and so may be pulled apart without damage, if it is done correctly.
My suggestion is to replace the fan with a mains powered one of the same dimensions and connect it to run constantly when the equipment is in use. AND, purchase a better quality replacement.

 

Often it is possible to lubricate bearings without disassembling a fan. But sometimes it is not, in which case replacement is needed. Mostly such small fans are a pressed together assembly, and so may be pulled apart without damage, if it is done correctly.
My suggestion is to replace the fan with a mains powered one of the same dimensions and connect it to run constantly when the equipment is in use. AND, purchase a better quality replacement.

MisterBill2,I disassembled the fan with no issue(i have experience with that action).Disassembling the bearing is the problem.It is so small size(5mm),that i can't figure out how to pull-out the seal(in order to reveal the metal spheres)and if you can actually disassemble that because i can't see how.
Beside that,Tonyr1024,suggested that even if it will be opened and lubricate,we can't be sure that it will be quite again(for long)as the bearing/race worn-out.
As you and other suggested,Yes,i should purchase a better quality replacement as the current one is probably the cause to the unusual behavior(which nsaSpook explain the reason),besides the noise issue.
Thanks.

 

No need to open the bearing just to lubricate it. They are not sealed so very well, so a drop or two of oil will penetrate after a few minutes. OR, put the whole bearing, by itself, submerged in a spoon ful of hot lubricating oil and let it cool. As it cools the air inside will shrink and pull in a bit of oil. That is a trick to oil those really small sealed bearings. They are not air-tight.

 

When connected directly to 12V supply outside it sound,i think,less loud than when it is inside the hi-fi at full speed.

Likely the reason why it seems quieter is because it doesn't have something solid to resonate off of. Like a guitar or a piano, strings alone don't make much sound. It's the resonation that occurs in the chamber of the guitar or the sounding board of the piano. Without mass to resonate off of it will sound quieter. When in the Hi-Fi it's louder because the metal frame amplifies (resonates) the sound.

No need to open the bearing just to lubricate it. They are not sealed so very well, so a drop or two of oil will penetrate after a few minutes.

I've had some success cleaning bearings using WD-40. But 40 is not a good lubricant. The WD stands for Water Displacement. Or that's what I've heard. However, with a sealed bearing, even though you can get some lube into the ball set it's hard if not impossible to flush out the junk. You might get something out but the more problematic particles are likely going to never come out. They may move but eventually they will find their way back into the ball races.

(semi quoted) I think that I better look for a good quite new fan, replace it and hope for the best.

You're on the right track.