Roland KR4500 weird fault

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StuUK
Posts: 1
Joined: 22:09, 19 January 2017

Roland KR4500 weird fault

Post by StuUK »

Hi All
I have a strange fault on my KR4500 intelligent piano that I have just acquired.
When cold and turned on there is continuous whooshing and crackling from speakers. Notes on the piano can hardly be heard and sound badly distorted almost like a distorted guitar with continuous sustain.

I thought at first it was a classic case of capacitors gone bad but it gradually improves all by itself and after 15 minutes it is working perfectly.

However it does this everytime from a cold start.
Its the same with headphones plugged in.
If i unplug the mainboard link from the amplifier and use an audio source on the input the sound is clean and clear so it isnt the amplifier causing this it is something on the main board.

There is no sign of damage on the main board or leaking caps but 4 or 5 of the caps have been replaced at some stage.

I think there is ether a dry joint somewhere that is healing itself with warmth or something similar internally on one of the chips.
I hope its the former, it doesnt seem to be behaving like a bad cap issue although that was my first judgement listening to the noise, but as i said after 15 mins all is fine.

My next plan was to start looking for any suspect solder joints and just resolder but this feels like groping in the dark.

Any suggestions or ideas?
Thanks
Stu
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