Piano World Home Page Forums Our Most Popular Forums Digital Pianos - Electronic Pianos - Synths & Keyboards Help! serious hum from Casio PX-130

I just purchased a used PX-130 with CS-67 stand and an SP-32 pedal bar. It's had little or no use, just basically sitting for the past 3 years. Only a couple marks and a fair amount of dust, now removed.

At the previous owner's house, it was played for about 20 minutes at various volumes, different tones, no issues. Removed the KB from the stand, wrapped in a blanket and put in our car for the ride home. Dusted KB on the way through garage by hand and with a little compressed air. Tightened up the stand screws, brought it inside and set it up. Plugged in, turned it on and starting about 25-33% volume setting, there was a very obnoxious AC hum type noise coming from both speakers. My wife the pianist, didn't have her "ears in", but it was loud enough she could hear it easily. There is no way it was doing that at the previous owner's house. It was very quiet in the house and I'd have heard it 20-30ft away. The higher the volume, the worse it gets. Both external speakers and headphone jacks sound the same. No other audio equipment/TV in our house is affected by AC hum noise. Even so, I turned off all breakers except for the one the keyboard was on, which also had a table lamp plugged in. No change. I turned on a different breaker and turned off the other. No change.
Based on the fact that nothing else in the house is affected by this type of hum, I'm guessing the problem is either the AC adapter, or one of the boards inside the piano. There were no loose connections or suspicious solder joints inside. If the AC adapter plug was more standard, I'd rig up the KB to run on battery as I have several 12V UPS batteries that would work fine for testing purposes.

I've looked for related problems on the web, but nothing found yet. I'd appreciate any help you can give for this as I'm scratching my head at the moment, not to mention sputtering and fuming about a potential 'waste' of $350. Everything works, but the hum is really obnoxious.

Thanks to all for reading.

I'm not really sure what the problem might be. I would advise against using compressed air to remove dust in the future, often it just wedges the dust further in where you don't want it.

Does the adapter sit snugly in the port? Or does it have a lot of wiggle room? Does fiddling with the adapter near the port (wiggling it, turning it) change the static level or sound at all?

You may need to get a replacement AC adapter. I'm sure you can purchase them from any Casio dealer. If it's someone local then perhaps you can return the adapter for a refund if the problem persists after trying it.

Thanks for your note; I was however careful to use low pressure and shield the areas where it shouldn't go. The dust was mostly in the gaps around the stand and indent lines in the plastic pieces and quite a bit underneath as it had sat over a floor register probably its entire life in that home. I think it hasn't been used hardly at all based on the condition of the keys. (The husband jabbed the wife a little as we were leaving, "Wow; she played that thing longer testing it out than you have since we bought it!") Despite a 1/2" x 3/4" scrape on the front rail, and a couple tiny nicks or scratches on the pedal bar, it's in very nice shape.

The adapter fits very snugly and it doesn't matter the orientation or whether it's fiddled with. I will probably run over to a local Guitar Center tomorrow or Saturday. I was thinking I may take the keyboard/adapter with me to get their impression, and also ask if I could use one of their display adapters for a moment just to try it out. Based on that, perhaps purchase a new one.

Thanks!

Sounds to me like a filter capacitor has become disconnected. Really shouldn't have happened as you took reasonable care bringing it home, but sometimes a manufacturing defect doesn't become apparent for a time. Especially if the previous owner never moved the board around. It might be something you can find yourself if you know what you are doing. Otherwise, take it somewhere to be repaired, shouldn't be too expensive.

Yes, give Casio a call and ask for information about servicing centres. With any luck, it should be a quick and simple fix.

James
x

SoundThumb & Kawai James -
Thanks! I didn't see any swollen caps nor were there any that appeared "loose" or badly soldered. I did wiggle them when powered on, but no change. I may have missed one or just not wiggled it the right direction.

I've written an email to Casio tonight, and will check out the AC adapter next since that's an easy one. Now that I've gone through the disassemble routine, it will go much faster next time, and if the adapter does no good, will look a little closer at the power supply board.

Update on the Casio; I tried moving it to different rooms, took it across the street away from the noisy transformer in our front yard and no change. Then took it for a ride in the car using an inverter; no change. So it's off to Guitar Center. No one with any keyboard expertise at G.C. tonight, but I tried the AC adapter in 3 different Casio keyboards, and no hum. So I guess I'll be calling a Casio service center and exploring other options.

So it's been some time, but after a fashion, I've made some progress. I checked into a Casio authorized repair facility and immediately dismissed that idea. $70 bench charge, clearly not a lot of in depth PX-130 knowledge at that place, and was told that they would likely replace 'a board'. The power supply/amplifier board would run $225, plus another $70 in labor, for a tentative total of $365, more than we paid for the keyboard.

Although he's an old time radio guy and NOT familiar with solid state circuitry, my dad suggested using a signal tracer. I finally received it a couple months ago. Using a PX-130 service manual as a reference and getting the basic logic flow of the board [I know just enough to be dangerous with electronics...] I began checking various components, specifically filter capacitors. By the way, the hum is ~82Hz, a poorly tuned E2. There weren't many places I could touch that didn't make a comparable noise to what was coming from the speakers. However, by far the loudest component was the voltage regulator, particularly the Vout terminal [the supply of 5V to the whole system]. It was several times louder, possibly an order of magnitude louder than anything else. After some discussion with dad, it seemed like a good possibility. It was making such a 'racket', it was easy to imagine it 'backfeeding' into the 12V side of the the board. So I've located a replacement voltage regulator at an Amazon vendor of all places, and hope to have them [it wasn't a lot more expensive to order 10 than it was for 1] within a week or so.
So if anyone comes across the post and has an annoying hum problem with their PX-130 or CPD-200 [uses the same voltage regulator], I'll have some extras and will post the results within a week or two.

Another bit of time later...

It turns out the Amazon vendor did NOT have any of the voltage regulators in stock; "they had gone missing and couldn't be found." ??? I searched and searched and found nothing in the US other than a few large wholesale houses requiring minimum orders of $100-$200. I was about to order some from a vendor on AliExpress in China, but the shipping was pretty high. So I checked one more time in a few likely places and a place that had been out of stock for months finally had some again! I ordered them on Wednesday and they came in the mail today. So either tonight or tomorrow, I'll swap out the voltage regulator and see if there's any change. If you're in need of a voltage regulator for your PX-130 or CPD-200 piano, let me know.

If you can get a separate power supply and temporarily substitute it for the one you have the problem might go away. 82 Hz is a rather odd frequency, so it's not likely to be AC hum. Originally I thought you had a grounding issue to your amplifier or a bad audio cable, but both of these problems would give you 60 Hz hum. If it's 82 Hz it must be some sub-multiple of the switching regulator. A bad output capacitor is a possibility. They tend to give out after a while. It may also be a bad solder joint on the output capacitor on the power supply.

Thanks for the response; I usually get notified when there's a response, but didn't get one this time...

To catch up, I did replace the voltage regulator. There might be a slight improvement, but very slight. I was getting ready to put it back together and noticed that Casio used known questionable capacitors on the power supply/amplifier board. They are CapXon brand, known to fail/swell/burst after some time. I just recapped an Acer monitor that had CapXon caps, all except two were swollen or leaking. I kicked myself for not seeing this before I ordered the voltage regulators, but decided while it was apart, I'd order some caps on the chance they were the problem. Just replaced those tonight with some Panasonic FC series and there is little or no difference. Since I got more than one voltage regulator, I was contemplating trying one more replacement. However, I just finished that and still humming.

Originally, I thought it may be the transformer sitting in our front yard, but nothing else in the house has the same hum. And that should have been 60Hz too. I'm reasonably sure it's not the power supply; I tried at a neighbor's house across the street [fed by same x-former however], grabbed an inverter and took the piano for a ride in the car and tried it that way. Still humming. I took the piano to a local Guitar Center and was going to try their power supply and/or my power supply in their pianos. I ended up just trying my PS in the 3 pianos on display. Absolute silence.

Recently I tried hooking it up to a 12V gel cell [before I ordered the voltage regulators]. Still humming. So in my mind, I've eliminated the power supply and believe that it's internal to the system most likely on the power supply/amplifier board. Using a signal tracer, the VR was by FAR the noisiest component and at the same frequency or very close to what's coming out of the speakers, so that's why I suspected it. There's hardly a component on the PS/A board, volume board, headphone board that didn't hum the same tune when I was probing around with the signal tracer.

I've also done some ground checks across board connectors and get good continuity. If you have any other ideas, I'm all ears. My dad has been trying to help long distance, but he's an old electronics guy and is not so familiar with solid state stuff. Still, he's had some constructive suggestions or given me ideas of stuff to try as well as shipping me his signal tracer.

Thanks again.

Probably one last post on this; still no joy on the hum issue, but while I had the piano disassembled I installed some external speaker jacks. At the moment, I'm using some relatively small inexpensive speakers from a bookshelf stereo, but the sound quality is much improved over the tiny 2"x5" internals mounted to a plastic shell. It's amazing what wood or a wood like substance can do to the sound of a speaker. The other bonus is that these speakers toned down some of the hum so that it isn't quite so obnoxious. Definitely still there and annoying, but not quite as bad.

Have you tried running the signal through something like this?

http://www.amazon.com/Kensington-Reducing-SmartPhone-including-iPhone/dp/B0031U1ATQ/

I'm had good luck getting rid of a nasty hum out of my iPad when I was using both the MIDI and AUX input on my board.

I suggest that you use this stereo filter on your line level outputs rather than the auto type.

http://www.radioshack.com/product/index.jsp?productId=2062214

I was going to suggest that perhaps nearby lighting dimmer might be the cause as this affects my system. However you have said that you have tried it with an invertor in your car. However such invertors do not offer a sine wave to your keyboard power input so you are introducing further potential noise.

Are you sure this is an 80Hz tone?

Is it the same as this:

Be careful and first turn down the volume on your computer sound.

https://www.youtube.com/watch?v=Lmx_jlgRIHE

Can you record it and post it here, or elsewhere so that its waveform can be examined by a spectral analyser. I can do this for you.

Ian

I have not; thanks for the tip! For it to work with the external speakers, I'm thinking I'd have to use a stereo to mono splitter on both ends, but hey, it's worth a shot. Thanks again!

Hello Ian -
Thanks for the response! I've not tried a filter like that. I'll add that to the to-do list. No dimmer switches in the house.

As far as the inverter, yes, I understand the further complications of introducing car induced interference, but the key thing to me is that other interference aside, the same tone persisted.

80Hz sample: Duh! Didn't think about searching on YT, but yes, although it sounds much different - lots of 'hash' mixed in, not a 'pure' tone - it sounds to me like the same frequency. Since the piano was on, I poked keys until I found a match. I do have a recording of the sound. It's a 280KB WMA file. I could either email it to you or put it on Dropbox. I don't see an option to attach files for the forum.

Thanks!

Ian -
Here's a link to the recording on Dropbox:

Casio PX-130 hum recording

Thanks for listening and/or analyzing.

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