Mini neon light whining power supply fix.

Thread Starter

Bod

Joined Sep 18, 2016
269
I recently got one of these mini neon light thingies:
IMG_0713.jpgThe problem with this is that the little power supply that comes with it creates an incredibly annoying whining noise. I could be totally wrong but I believe that's because it converts dc to ac, with no filtering, then steps it up through a transformer which creates the whine.
Here's some pictures of the little power supply (it uses two AA batteries for power):
IMG_0706.jpgIMG_0712.jpg(Excuse the bodge soldering. When it arrived, before I had even opened it, the battery terminals were poorly soldered and they were lifting the pads, so I had to scrape away some solder mask and solder to the bare copper).

I did some voltage readings at the output - note: my multimeter has been acting up recently, so I've got multiple readings, all at different voltages. These were all measured with the neon lights unplugged.
The first one I got was 200VAC but obviously at very very low current.
The next was 25VAC
And finally, 65VAC - 11VAC when the light were plugged in
(probably time for a new DMM!)

My original idea was to remake the power supply but I don't have accurate current draw readings, I don't have accurate output voltage readings, so it would be quite hard I think.

However, there must be some bodge component(s) that I can put in place to remove the whining.

Here's a little clip of the whining noise:
 

Tonyr1084

Joined Sep 24, 2015
4,383
The whine is probably caused by an AC cycle that is in the audible range of human hearing. That's typically 20 Hz to 20,000 Hz. And there's a black dot on the board which means it probably is where the frequency is controlled. But I don't know that for a fact - so don't run to the bank with that.
my multimeter has been acting up recently
As far as the meter acting up - I had that happen one time. Checking a 12 volt battery I noticed the voltage started to rise into and through 13 volts and 14 volts. After a short while the 12 volt battery was reading over 15 volts. That can't be. There must have been something wrong with the meter. And there was. A dying battery in the meter. When I put a new battery in it the meter returned to reading a normal voltage. You might have a weak or dying battery in your meter.
 

Dodgydave

Joined Jun 22, 2012
9,084
The Black Blob is a microcontroller, looks like a push-pull transformer step up converter,, the whine will be the transformer whistle, you could cover it in wax or varnish to stop it..
 

Thread Starter

Bod

Joined Sep 18, 2016
269
The whine is probably caused by an AC cycle that is in the audible range of human hearing. That's typically 20 Hz to 20,000 Hz. And there's a black dot on the board which means it probably is where the frequency is controlled. But I don't know that for a fact - so don't run to the bank with that.
Would there be a way to fix that?
you could cover it in wax or varnish to stop it..
I have though about covering the transformer but I'm not sure how well that's going to work.
Is there not any filtering I can use get rid of this?
As far as the meter acting up - I had that happen one time. Checking a 12 volt battery I noticed the voltage started to rise into and through 13 volts and 14 volts. After a short while the 12 volt battery was reading over 15 volts. That can't be. There must have been something wrong with the meter. And there was. A dying battery in the meter. When I put a new battery in it the meter returned to reading a normal voltage. You might have a weak or dying battery in your meter.
My battery is definitely getting flat, I just don't have anymore at the moment to put in. I also have a partially blown fuse on the board I need to replace. I'm hoping it's not a case of 'the fuse should have blow but it didn't so its damaged something on the board'. It is a slow blow so that shouldn't be the case.
 

Dodgydave

Joined Jun 22, 2012
9,084
I recently got one of these mini neon light thingies:
View attachment 200992The problem with this is that the little power supply that comes with it creates an incredibly annoying whining noise. I could be totally wrong but I believe that's because it converts dc to ac, with no filtering, then steps it up through a transformer which creates the whine.
Here's some pictures of the little power supply (it uses two AA batteries for power):
View attachment 200993View attachment 200994(Excuse the bodge soldering. When it arrived, before I had even opened it, the battery terminals were poorly soldered and they were lifting the pads, so I had to scrape away some solder mask and solder to the bare copper).

I did some voltage readings at the output - note: my multimeter has been acting up recently, so I've got multiple readings, all at different voltages. These were all measured with the neon lights unplugged.
The first one I got was 200VAC but obviously at very very low current.
The next was 25VAC
And finally, 65VAC - 11VAC when the light were plugged in
(probably time for a new DMM!)

My original idea was to remake the power supply but I don't have accurate current draw readings, I don't have accurate output voltage readings, so it would be quite hard I think.

However, there must be some bodge component(s) that I can put in place to remove the whining.

Here's a little clip of the whining noise:
Can't view this,,,got a,youtube video or mp3??

It will be Line Whistle from the transformer inductor windings.. Like the old line time base in TV sets..
 

Tonyr1084

Joined Sep 24, 2015
4,383
I also have a partially blown fuse on the board
Just me being stupid - but I've never heard of a partially blown fuse. Well, as I think back to when I did failure analysis, I did find a trace partially burned due to static discharge; so maybe. But likely the fuse is going to be good or bad, not partially good or partially bad. And the fuse may have something to do with amperage reading. May be a 0.3A fuse (300 mA) if memory serves.
 

Thread Starter

Bod

Joined Sep 18, 2016
269
Just me being stupid - but I've never heard of a partially blown fuse. Well, as I think back to when I did failure analysis, I did find a trace partially burned due to static discharge; so maybe. But likely the fuse is going to be good or bad, not partially good or partially bad. And the fuse may have something to do with amperage reading. May be a 0.3A fuse (300 mA) if memory serves.
I probably should have explained it more! Since the fuse is a slow blow, it.... blows slowly. So during the time it was blowing, I must have stopped what I was doing, so it put the fuse into 'limbo'. It's halfway there to being fully blown, but also still conducts electricity fine. Here's some images:
IMG_0716.jpgIMG_0715.jpgThey're not the best but hopefully you can see what I mean!
 

Thread Starter

Bod

Joined Sep 18, 2016
269
No just 4 seconds of snooker..
To be fair, it is quite hidden especially since not only was my phone moving, but my power supply was also on.

EDIT: I did my best to match the frequency of the sound using my function generator. I believe the whining is about 9.5kHz since that was what sounded closest.
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
4,383
WOW! That screw looks HUGE. Therefore so must the fuse be. A dime or a quarter would be a better size reference. But not to be picky, if the fuse is still conducting electricity then it's not blown. I've never heard of a fuse having a cumulative damage. It may have gotten hot, which might have changed its characteristics - but in the end the best thing is to replace the fuse with the type that should be there. There's a HUGE difference between a 2 amp fuse and a 2 amp slow blow fuse. The slow blow can do significant damage to sensitive circuitry. The fast blow fuse should protect small sensitive electronics "Fast", whereas the slow blow may be better suited for things that draw a heavy startup current but stabilize quickly. A slow blow fuse is not recommended for that tiny circuit. At least that's my thinking. If someone disagrees - that's fine too.
 

Thread Starter

Bod

Joined Sep 18, 2016
269
OW! That screw looks HUGE. Therefore so must the fuse be. A dime or a quarter would be a better size reference.
I didn't even mean for the screw to be the size reference; it's all I had on hand when I was trying to stop the fuse from rolling around!
The fuse it just the same size a any average fuse. It looks bigger probably because it's zoomed in.
but in the end the best thing is to replace the fuse with the type that should be there. There's a HUGE difference between a 2 amp fuse and a 2 amp slow blow fuse.
The slow blow is actually what came with the DMM. I have some glass slow blows but they aren't the correct blow time (or amperage), so I need to get some more.
I will try with a new battery first though.
The slow blow can do significant damage to sensitive circuitry. The fast blow fuse should protect small sensitive electronics "Fast", whereas the slow blow may be better suited for things that draw a heavy startup current but stabilize quickly.
If I recall correctly, this (sort of) blown fuse is across COM and the uAmA terminals on my DMM. I guess that makes sense with what you described.

EDIT: I read back across an earlier reply and I said: 'I also have a partially blown fuse on the board I need to replace'. You mentioned: 'A slow blow fuse is not recommended for that tiny circuit' That fuse is from the board of my DMM, to clear up any confusion.
 

Reloadron

Joined Jan 15, 2015
5,361
The Black Blob is a microcontroller, looks like a push-pull transformer step up converter,, the whine will be the transformer whistle, you could cover it in wax or varnish to stop it..
That's where I would start. Short of a vacuum / pressure impregnation process I would try and force some varnish into the transformer and coat the windings. Hopefully that will quiet it down. Normally when something whines I offer it a little cheese to go with the whine. :)

Ron
 

MisterBill2

Joined Jan 23, 2018
5,796
The noise is caused by the changing magnetism in the transformer, so it is a mechanical problem and the solution is a mechanical fix. BUT FIRST the whole package needs to have external connections available, which means wires soldered on to the connection points so that the entire module can be sealed in a sound deadening material. What materials are available will depend on what part of the world the TS is located in, and how much can be spent on the material.
 

Sensacell

Joined Jun 19, 2012
2,567
I agree that the noise is from the transformer core- nothing you can do about it- besides some draconian mechanical sound isolation.

Extending the wires to the transformer and potting it in RTV silicone or wax might work... a big pain for little gain.
 

MisterBill2

Joined Jan 23, 2018
5,796
I agree that the noise is from the transformer core- nothing you can do about it- besides some draconian mechanical sound isolation.

Extending the wires to the transformer and potting it in RTV silicone or wax might work... a big pain for little gain.
I was suggesting extending the wires from the complete module, not the transformer, and then indeed putting the whole module in a fairly solid encapsulation. The cheap fast-setting epoxy, thinned a bit with mineral spirits, will certainly quiet the whole thing a lot. Even tar, melted and poured, with a suitable housing, would be quite effective, but extremely messy. At one time tar was used quite a lot on transformers, since it was cheap, easy, and also a fairly good electrical insulator, and it is also water proof.
 

Thread Starter

Bod

Joined Sep 18, 2016
269
Thanks for all the replies. It seems covering the transformer is the best solution (apart from rebuilding the power supply, but that's for the future)

or I could just put up with it!

Bod
 

MisterBill2

Joined Jan 23, 2018
5,796
Thanks for all the replies. It seems covering the transformer is the best solution (apart from rebuilding the power supply, but that's for the future)

or I could just put up with it!

Bod
An application of silicone rubber material could be fast and easy and may make a very large difference. Possibly a bit messy, but not if you are really careful.
 
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