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Old 25th Sep 2022, 3:10 pm   #1
sourbiscuits
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Default [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Greetings to all the members!

I recently got myself a Uher Report Monitor 4000. However, I am experiencing a very odd situation with it.

When I got the unit, the reels were not spinning at all, but the motor was engaging. Didn't take me long to figure out there was a molten belt. I cleaned all the excess molten belt bits from the device and installed a rubber band just for the sake of testing the unit.

Once I engage the play button, regardless if there is a tape threaded or not, I am getting a rather loud low frequency noise. It sounds like a mechanical noise being picked up. It goes out from the built in speaker and I also tried the TRS 6.3 headphone output. I have not yet tested the rest of the outputs.

The most interesting fact about this is how the PCB is related to this. The PCB is mounted on hinges. If I engage the play button WITH the long yellow belt (rubber band) attached to the motor and I open the PCB up, the signal goes away. If I close the board, the more I close it the stronger the signal becomes. As of this, I also tried the same thing without the belt attached. If I am to remove the belt, the signal is gone regardles if the PCB is opened or closed.

I am sharing a short video test of the above to show what I mean -

https://www.youtube.com/watch?v=9_Oqz8eT-uU

Here is a test recording with all speeds. from fastets to slowest - https://on.soundcloud.com/afSSk

Ever since I found the PCB situation, I was suggested it's the drive wheel rubber being hardened that causes the noise. Today I did the same test with the PCB with the drive wheel removed (bras fly wheel still installed and attached to the motor with a belt). The result was the same. Same noise was coming out.

On the photo below, I have marked the elements I suspect are causing this and when engaged cause the signal to appear and I ruled out the big drive wheel based on the last test.

I am really stuck with figuring this out. Any suggestions on fixing this would be greatly appreciated.
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Old 25th Sep 2022, 4:18 pm   #2
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Hello and welcome to the Forum.

Yes does seem odd indeed.

The noise we discussed in PM (from my old Thread) was definitely different, being mechanical noise (mainly on top speed) largely caused by the rubber bonded drive wheel, this noise did not get picked up by the electronics/did not output on speaker or line outputs.

Really hard to guess what root cause is. Maybe something not quite right with the electronic drive signals to the motor and with the belt fitted this leads to some electrical noise that is being picked up by the PCB when it is close to the motor.

Not easy to do but would suggest scoping the motor drive signals with and without belt fitted and with PCB close to/away from the PCB.

Also with the PCB upright (so no noise) trying moving/flexing the cable loom to see if any similar noise can be generated, am wondering if there could be a damaged cable/cable screen that is being stressed when the PCB is hinged down.

Is the motor firmly in its mounting jacket ?

David

Last edited by DMcMahon; 25th Sep 2022 at 4:24 pm.
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Old 25th Sep 2022, 4:37 pm   #3
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

I am wonderng if the belt is getting charged up (like a van de Graff generator belt) and this is somehow causing noise in the amplifier.

You could try arranging temporary earthing contacts to press against the belt and see if this makes any difference.
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Old 25th Sep 2022, 5:27 pm   #4
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Some of the 40xx models have a little conductive brush that the motor drive belt drives through, presumably to discharge static.

David
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Old 25th Sep 2022, 7:52 pm   #5
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Photo attached showing the brush that the long black drive belt goes through.

Would recommend that a correct rubber drive belt is used for the motor in case the green elastic band is part of the problem.

David
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Old 25th Sep 2022, 10:18 pm   #6
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Welcome! It looks like the resident Uher expert is on the case.

I'd try to narrow it down further. Remove the belt - is the noise still there? If not, then perhaps it's the flywheel bearings. Can you hear any noise with the loudspeaker turned off and no headphones plugged in (is the noise mechanical and audible)?

I haven't got a Report Monitor, but my experience with Report-Ls would suggest that there's enough room inside for some judicious poking about as suggested above.
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Old 26th Sep 2022, 8:57 am   #7
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

First off, thank you very much for your inputs!

So I want to confirm that the motor alone doesn't cause interference in my opinion. I have already tried removing the rubber band and with the motor on, with the PCB opened or closed, the noise isn't there. The motor is well fitted in the socket. I tried the same without the drive wheel. When the belt is attached, the noise is there - that tells me it's not the drive wheel?

So as of the above I believe I covered @DMcMahon suggestions. I will try the cables today, see if that makes any difference.

As for the input of @TonyDuell, I also have a brush in my unit (really wondered what it was for).I believe it was in contact with the rubber band, so I think that creates a grounding point? I will tweak it as well today.

I'll keep you updated of today's progress.
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Old 26th Sep 2022, 10:03 am   #8
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

What about Uncle Bulgaria's question if the noise in question is audible mechanical noise with speaker turned down and no headphones connected ?

David
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Old 26th Sep 2022, 10:55 am   #9
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Ok, so I made sure the belt is in good contact with the brush. At first I thought there's a bit of a difference but the reality was that there wasn't. I didn't see the reply of Uncle Bulgaria when I ledt mine. In response - no noise when the belt is detached. Noise is there when attached and even tried removing the drive wheel. So belt attached and flywheel only also results with the same noise. In all honesty, I don't hear a very distinctive noise from the motor itself. I do have the impression it's the flywheel bearings or an electromagnetic interference. I used a digital eq to view the frequency range and it's appearing in the low end.

Lastly, yes, the rubber band is only temporary. I am planning on buying a new belt set. I just find it highly unlikely that the belt is causing the issues.
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Old 26th Sep 2022, 11:28 am   #10
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Yes agreed that unlikely that noise is due to belt but would be good to get the belt possibilty out of the equation, especially as the noise is not present when belt is removed.

Whether it is the load of the belt on the motor that creates the noise from the motor or whether it is the rotating brass flywheel that generates the noise is very difficult to imagine, I personally would think more motor related.

It certainly is an interesting fault but of course is very frustrating for you.

David
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Old 26th Sep 2022, 11:42 am   #11
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Can you run the belt around a little stick or something while it's attached to the motor, keeping tension on and testing the motor while taking the brass flywheel out of the equation?

It is peculiar. If it's not mechanical then it should occur with the motor on whether the belt is connected or not. I find it an unlikely hypothesis that the belt formulation would cause such a strong electromagnetic field as to couple into the amplifier circuitry.

Is the motor the same as the CR series, where a set of opening and closing contacts clatter on startup? If so, I guess there could be some coupling of that into the audio circuitry from a faulty component when the motor's up to speed.
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Old 26th Sep 2022, 5:23 pm   #12
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

This sounds like an induced noise from the motor windings/cabling getting into the sensitive playback amplifier. If the temporary rubber band is too tight, the motor current will be higher than it should be and that will increase the level of noise induced into the amplifier.

It's probably best to try a set of proper belts and then worry about any noises which remain once they have been fitted.

Paula
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Old 26th Sep 2022, 9:14 pm   #13
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Guys, again I'd like to thank you for all the inputs. Today around midday I actually came to the conclusion that it must in fact be the temporary rubber band I installed for the sake of testing the playback feature..

Here's what I did today: Removed the big (drive) wheel. Then removed the fly (brass) wheel. No noise was coming out of it when I rotated the wheel alone. Smooth as butter. I then attempted to do what чичо (I'm also bulgarian) Bulgaria suggested and just held the flywheel as the rubber belt was attached to the motor. Then I was enlightened... Since I was pulling the band by hand, it was tighter than while it was fitted in. And right before my eyes the band became wobbly. It then struck me. I removed the band from thr roles and I just pulled it with my fingers. If you do that and strike the band it makes a rubber sound.. A rather lower pitched sound any pulled string would do. I can only guess but I am strongly convinced now (contrary to my last post) that it must be the lack of propper belt causing the wobbly noise coming out.

I am ordering a new set of belts and am hoping to get it by Friday this week. I will post an update in the thread. I once again thank you for the help! Your last three responses really confirm my latest discovery.

I'll stay in touch!
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Old 6th Oct 2022, 5:35 pm   #14
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

Guys, thanks again for all the tips! I am very happy and relieved to conclude and solve the thread with the fact it was the rubber band / lack of proper belt causing the irritating noise. I am still waiting for the original belts I ordered from SDS, however, since I returned home with the unit, I remembered today that I had some old belts laying around. I placed one and the output sounds amazing now. Hopefully my ignorance will help others in the future.

Best,

- Kyle
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Old 6th Oct 2022, 5:50 pm   #15
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

I guess I'm too curious (like a cat?) but I would want to know _why_ thr rubber band caused the noise. Too much load on the motor? Getting charged up? Or something else.
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Old 6th Oct 2022, 6:21 pm   #16
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

My logic behind it was the material it's made of. It's much softer and it creates vibrations which the chip seems to catch/hear. When it's pulled it becomes like a spring. Also the type of material seems to give more vibrant wave compared to the one of the belt. I believe the belts are harder. When I placed the belt tonight, I didn't notice it was in contact with the metal pin of the brush. When I powered it on the noise was harshly louder. I detached the belt from the brush. The signal was as pure as it gets.. I am yet to run it through a eq and see what is going on but I can most definitely hear a big difference!
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Old 6th Oct 2022, 9:13 pm   #17
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

That sounds really good news.

David
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Old 6th Oct 2022, 9:24 pm   #18
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

I just did the eq test. I am very pleased. There is still a liiittle bit of low end mud, but I think it's likely due to the lack of lubricant and the belt I'm using is thinner than what it should be. Either way, I am currently satisfied with it and very relieved I got rid of the main rumble! I want to wait until I get the new belts, run some more proper tests and post some better examples.
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Old 10th Oct 2022, 9:48 pm   #19
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

I want to once again confirm the good results. The belts have arrived and I installed them. The EQ test is perfect. The machine works surprisingly well considering it's age. I am very greatful for your patiance and all knowledge you shared. I hope this thread will help others.

- Kyle
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Old 11th Oct 2022, 11:13 am   #20
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Default Re: [HELP NEEDED] UHER Report Monitor 4000 mechanical noise/hum

That is great news Kyle.

When you say EQ test, do you mean Equalisation, Frequency Response or something else ?

David
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