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Joined: Dec 2020
Posts: 38
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Nigo Offline OP
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Hello,

I bought a P120 that's not working as it should (and got scammed). Sound is only coming through the right channel. I thought about the speaker being dead because on the headphones it seamed to work at first, except it does not, the seller used a jack adapter that puts the right channel to the left...

Anyway, I got no sound to the left speaker, the left line out, the left side of headphone.
The speaker DOES turn on (there is noticeable white noise) and, when tested on a ohm-meter, the resistance on the left line out and headphone is exactly the same as on the right, piano turned off or on (which means no short-circuit).

Here my electronic knowledge runs out. I'm not sure whether it could be linked to the amplifier board or not.

I dismantled he piano and it looks exactly like the naked pictures of dewster here. Very clean, nothing look burned or anything.
https://web.archive.org/web/20180529155930/http://forum.pianoworld.com/ubbthreads.php/topics/1439246/NEKID%20PICTURES!!%20%20(Yamaha%20P120.html

I'm thinking of replacing the LA4705N chip (15w 2-channel Power Amplifier) as it is cheap and seams reasonably easy to replace, but I'm not 100% sure that could be the source of the problem.

If you have any advise, please do smile

Last edited by Nigo; 06/15/21 02:59 AM.
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Nigo Offline OP
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I found a damage on the jack board that could explain the problem, so I'll try to fix that

https://ibb.co/M66xPsh
https://ibb.co/X45Yfzw

Joined: Apr 2021
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For an old school budget diagnostic tool, get a piezoelectric ear piece and wire it up to multimeter probes. You can then safely listen to audio signals anywhere on the board and trace faults. It has a high resistance so you can connect it pretty much anywhere without risking damage or injury.


Roland FP30, VILabs etc, adult beginner. Get your personal pianist emojis: Emoji Me App
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Nigo Offline OP
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Fixed. I soldered a wire on the blue line that was burned out.
Thanks,

https://ibb.co/XZ7dkg4

Joined: Aug 2017
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Is there an electrolytic capacitor nearby? This looks like a leak. Make sure you clean the board to minimize recurrence of the problem. And replace bulging capacitors or ones that look to be leaking.


Kawai ES8, Roland RD2000, Yamaha AG06 mixer, Presonus Eris E5 monitors, Sennheiser HD598SR phones.
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Nigo Offline OP
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is DOES look like a leak I know, but there is nothing nearby. The capacitors on the other side (looking down) are all fine (I tested them), maybe the resistance of the right line leaked... I don't know. Looks like a pain to replace anyway
my opinion is that the previous owner plugged a bad amplifier and shorted the whole thing, enough for the (very thin) track to melt. And for some reason did not fix it and sold it to an idiot. A proficient idiot.
the resistances between the channels are identical and anyway piano works great as is. NOW it does smile

Last edited by Nigo; 06/16/21 05:42 AM.
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Hello,

@Nigo, Congratulations on a nice repair and a now working piano! Maybe it was a scam, but now extra pride and satisfaction are yours.

@MarkOfJohnson, I love your piezo probe tester idea! As I am restoring some nice Onkyo amplifiers (for the piano) that may well be a handy thingy.

Cheers and happy repairs,

HZ


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