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Help please with a fault
#3009519 Yesterday at 02:25 PM
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Hi- i was hoping someone might be able to advise on what the fault is and how to fix on my digital piano please. It is a yahama ydp-161 and is 8yrs old. It has recently started buzzing which initially was quiet but has got louder and louder. I have located what is causing the noise but I am not sure what it is and whether it is terminal! Any help and advice would be greatly appreciated.


Re: Help please with a fault
Benfolds81 #3009527 Yesterday at 02:58 PM
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It seems that the buzz is coming from the power transformer.
If there is any looseness between the iron laminations in core, or between the windings and the core, then you'll get this buzzing sound.

Does the piano work properly? If so, then ignore the buzz ... if you can.
If it's too loud to bear then you might need a replacement transformer.
Or ... a talented tech might apply some rubbery compound around the windings or the core to absorb the vibration.

Re: Help please with a fault
Benfolds81 #3009540 Yesterday at 03:21 PM
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Take a wooden stick, Poke the component you suspect is buzzing, if the Frequency / Characteristic of the buzzing changes as that component is poked, you know that's the thing that's buzzing.

Transformers are cheap though, so you can just buy another one, it doesn't have to be the exact one, as long as it physically fits, you can wire them up.

Silicone glue, or Potting compound is what they use to dampen noise.

Last edited by jeffcat; Yesterday at 03:22 PM.
Re: Help please with a fault
Benfolds81 #3009551 Yesterday at 03:38 PM
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Not so fast, jeffcat.

I found the service manual. The transformer for this piano comes in several different flavors, depending on region.
All versions have three secondary windings. The secondary voltages are not specified on the schematic. frown

Re: Help please with a fault
Benfolds81 #3009560 Yesterday at 04:17 PM
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I would start by checking the usual suspects, the electrolytic capacitors: if they are not bulged, if there is no sign of leaks on the PCB.


Kawai ES8, Roland RD2000, Yamaha AG06 mixer, Presonus Eris E5 monitors, Sennheiser HD598SR phones.
Re: Help please with a fault
Benfolds81 #3009595 Yesterday at 06:08 PM
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Loosen the screws holding down the transformer but don't remove them. Wedge perhaps two mm of folded paper directly under the center of the transformer where the laminations are. The thickness has to be enough for the screw tabs to now be a little above the surface they are screwed into, Tighten the screws. See if this helps,

Re: Help please with a fault
NormB #3009668 Yesterday at 09:14 PM
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Originally Posted by NormB
Loosen the screws holding down the transformer but don't remove them. Wedge perhaps two mm of folded paper directly under the center of the transformer where the laminations are. The thickness has to be enough for the screw tabs to now be a little above the surface they are screwed into, Tighten the screws. See if this helps,

That solution sounds a bit dangerous (fire) to me.

No chance of that ?


Don

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Re: Help please with a fault
dmd #3009697 Yesterday at 11:53 PM
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Originally Posted by dmd
Originally Posted by NormB
Loosen the screws holding down the transformer but don't remove them. Wedge perhaps two mm of folded paper directly under the center of the transformer where the laminations are. The thickness has to be enough for the screw tabs to now be a little above the surface they are screwed into, Tighten the screws. See if this helps,

That solution sounds a bit dangerous (fire) to me.

No chance of that ?

Yes it is.. if you're gonna wedge something , use silicone pads. the same stuff they use to mute pianos.

Re: Help please with a fault
dmd #3009710 18 hours ago
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Until plastics were improved decades ago transformers routinely had paper wrapping between windings.
Originally Posted by dmd
Originally Posted by NormB
Loosen the screws holding down the transformer but don't remove them. Wedge perhaps two mm of folded paper directly under the center of the transformer where the laminations are. The thickness has to be enough for the screw tabs to now be a little above the surface they are screwed into, Tighten the screws. See if this helps,
That solution sounds a bit dangerous (fire) to me.
No chance of that ?

Re: Help please with a fault
Benfolds81 #3009724 16 hours ago
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Thanks for all the replies - will see how I get on!

Re: Help please with a fault
Benfolds81 #3009739 14 hours ago
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One thing about the transformer, it may be warm but not hot. If hot to the touch, there may be a short in it that could cause the noise. Extremely unlikely though.


Kawai ES8, Roland RD2000, Yamaha AG06 mixer, Presonus Eris E5 monitors, Sennheiser HD598SR phones.
Re: Help please with a fault
Benfolds81 #3009781 9 hours ago
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Quote
Until plastics were improved decades ago transformers routinely had paper wrapping between windings.

Indeed they did. Very high voltage ones like we used to use in amateur radio transmitters even impregnated the paper with waxy stuff to increase the insulation value of the paper. Zero fire risk here, but a silicone pad is a better option in any case, if available.

Re: Help please with a fault
Benfolds81 #3009782 9 hours ago
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If the shim underneath does not help there's another possible thing to try. That transformer is a bit unusual because it has a metal can around much of it that I presume is there as magnetic shielding. It may be a completely separate part from the transformer underneath. If so, it may be the cause of the noise, vibrating because of the magnetic field of the transformer. If it is a separate part some judicious shimming between it and the enclosed transformer might stop the noise.

Re: Help please with a fault
Benfolds81 #3009791 9 hours ago
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Please, note that such a humm could be caused by a secondary fault: if the bridge rectifier (the 4 legs black component at the left of the transformer) has an open diode (it is made of 4 diodes, two per brach), the unit will be working as a half-wave rectifier. That would generate a 100 or 120Hz humm, depending on mains being 50 or 60Hz.

To diagnose it, you would need a diode checker. Or you can be brave enough and replace the diode bridge. With some soldering practice it is dead easy to do.


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Re: Help please with a fault
Benfolds81 #3009831 7 hours ago
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Note that a diode checker can be a simple low-cost multimeter from your local hardware store. Anything that can read resistance (ohms) will work and you don't need it to be particularly accurate since you're just checking for presence or absence of resistance, so the $9.95 handyman's special multimeter will be all you need to test it.

Or you could check it with a $1500 Fluke meter. smile


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Re: Help please with a fault
EB5AGV #3009914 3 hours ago
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Originally Posted by EB5AGV
Please, note that such a humm could be caused by a secondary fault: if the bridge rectifier (the 4 legs black component at the left of the transformer) has an open diode (it is made of 4 diodes, two per brach), the unit will be working as a half-wave rectifier. That would generate a 100 or 120Hz humm, depending on mains being 50 or 60Hz.

To diagnose it, you would need a diode checker. Or you can be brave enough and replace the diode bridge. With some soldering practice it is dead easy to do.

Data venia, just a correction, half wave would produce 50/60Hz (fundamental). Full wave would produce 100/120.


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Re: Help please with a fault
EVC2017 #3009922 3 hours ago
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Originally Posted by EVC2017
Originally Posted by EB5AGV
Please, note that such a humm could be caused by a secondary fault: if the bridge rectifier (the 4 legs black component at the left of the transformer) has an open diode (it is made of 4 diodes, two per brach), the unit will be working as a half-wave rectifier. That would generate a 100 or 120Hz humm, depending on mains being 50 or 60Hz.

To diagnose it, you would need a diode checker. Or you can be brave enough and replace the diode bridge. With some soldering practice it is dead easy to do.

Data venia, just a correction, half wave would produce 50/60Hz (fundamental). Full wave would produce 100/120.

Opps, sorry, I goofed!

All in all, the humm (50 or 60Hz thumb) can be due to what I described, as that bridge failure means the transformer is stressed only on half period of the sinewave, and that could create the humm (let's say the transformer becomes a buzzer)


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Re: Help please with a fault
Benfolds81 #3009930 2 hours ago
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I am both impressed and daunted! Haven't tried any soldering since school! Thanks once more for the responses and superb knowledge out there!

Re: Help please with a fault
Benfolds81 #3009934 2 hours ago
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All of this remote diagnosis is moot until the OP responds to the question: Does the piano work right now?

As for a diode being open ... not likely. Diodes short. They rarely open.

Re: Help please with a fault
MacMacMac #3009939 2 hours ago
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Originally Posted by MacMacMac
All of this remote diagnosis is moot until the OP responds to the question: Does the piano work right now?

As for a diode being open ... not likely. Diodes short. They rarely open.

Well, I am working with electronics for close to 40 years... and have found quite a lot of diodes open in power supplies bridges. Yes, not all die that way, but, trust me, they die open also.

You can read very interesting info on this here:

How to Troubleshoot a Diode Bridge Rectifier

Scroll down for what I commented.

Last edited by EB5AGV; 2 hours ago.

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