Roland HP-1 Digital Piano with noise fault - diyAudio
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Old 6th December 2013, 07:36 PM   #1
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Default Roland HP-1 Digital Piano with noise fault

Theres an annoying noise immediately from powering on the piano that is constant at regular intervals. The volume control does change the noise volume level, turn up the volume control and the noise gets louder, turn down the volume control and the noise gets quieter. With the volume control all the way down the 'fault' noise cannot be heard.
The noise is heard through both left and right built-in speakers, external speakers connected to the output jacks and also heard through headphones.
The noise is still there when an external input source is connected.

I have an audio file of the 'fault' noise as I would rather not try to describe it when that could be misleading and time wasting with troubleshooting.
I am new here so may have to wait until I have posted a few more times.

Hope this is enough detail for someone to be able to help/advise.

Very grateful for any help.
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Old 7th December 2013, 08:35 AM   #2
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Some pictures of the boards, these may help identify the layout and a qualified eye may spot something.
A SM is also linked for anyone willing to help.
¡¾ROLAND¡¿HP-1-Service Manual[Software Manual][Parts Catalog][Quick Start][User Guide][Circuit Diagrams]Download -Roland-Service Manual,Software Manual,Parts Catalog,Quick Start,User Guide,Circuit Diagrams
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Old 7th December 2013, 09:33 AM   #3
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xfmr
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Old 7th December 2013, 09:44 AM   #4
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Main board
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Old 7th December 2013, 10:09 AM   #5
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Power / Amp board
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Old 7th December 2013, 12:34 PM   #6
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I'm guessing either this thread is in the wrong place or this fault is not a common one amongst amp circuits. I was hoping this would be a generic amp cct fault, related to an op amp or inverter I.C, but perhaps its more specific to this kit (piano) and maybe the fault lies with the DAC or CMOS ASIC.
Most common noise faults seem to be clicks,ticks,hum,buzz which this is not under any of those categories.
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Old 7th December 2013, 01:37 PM   #7
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Is it possibly a pot causing this?
Is the noise consistent with this type of fault?
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Old 7th December 2013, 02:14 PM   #8
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Control board
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Old 7th December 2013, 02:34 PM   #9
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If this thing is 15 to 20 years old, then reseating connectors and changing all the electrolytic capacitors on the power board may help. Ribbon connectors are not really reliable at signal levels, or any tin and brass connector really. Removing and replacing will scrape some oxide off, and sometimes spraying with contact cleaner helps even more. But we found in the factory we had to replace a lot of ribbon cables because the push-in connections weren't making any more to the copper in the ribbon. You can buy ribbon and connectors from major distributors if you can take measurements and count pins and read a datasheet. You can make a ribbon connector installer jig by taking two pieces of board and putting screws through the ends.
15-20 year old electrolytic capacitors don't filter the power supply properly and allow all sorts of bad things to happen. Here is a post by a guy that repaired a roland digital instrument just by replacing the two power caps. Roland Jazz Chorus 77 He had a high pitched squeal.
Mark your board for + with a sharpie before removing any e-capacitors, if you put the new one in backwards it blows immediately. Newer capacitors have a minus in balls pointing at the minus lead, instead of a + pointing at the plus. Use safety glasses unsoldering. I buy capacitors with >3000 hours service life so I don't have to do the job again in three years. I'd start with the ones located nearest the fuses, as probably those are the main power filters. I do two parts at a time and check my work by reassembling and listening, as if I make a bad solder joint or other error and the sound gets worse, I know exactly where the problem will be.
Weird digital problems are often problems in the capacitors in the power supply areas. The mother board in this PC I am using had an ittermittant problem, and I replaced a couple of nasty looking capacitors near the line printer port, which I wasn't even using. Problem solved, hasn't happend again for a year. **** ROHS solder is a pain to remove. After I got the capacitors out with a 130 W pistol soldering gun, I had to drill the solder out of the holes with a #60 drill. Saved me $100 for a used computer though. Most any other used computer has 5 years old or older capacitors in it too. Computer capacitors are the worst, 500 hour design life at the most I suspect. Some brands like Teepo you only see in computers. I go through a PCAT switcher power supply every year. One day I'll learn to fix those, too, but new ones are only $29 so an intellectual interest, only.
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Last edited by indianajo; 7th December 2013 at 02:46 PM.
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Old 7th December 2013, 03:06 PM   #10
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Can certainly check connections and cables but would think movement of the cables and connections would affect the fault noise, which it does not.
Not conclusive I know but have checked caps for fluid leaks and bulging and in-circuit ESR, all of which appear ok.
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