Question about Music
It's likely capacitors discharging, then re-charging during power-up weakens the fuse element. Try a slightly bigger fuse (1.5A)
Also, if you have some contact cleaner (NuTrol is best) try cleaning the power switch as intermittant action can confuse switching supplies.
Posted on Nov 30, 2014
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Posted on Jan 02, 2017
SOURCE: korg C-15 S concert piano
ik heb 20 jaar geleden een korg c 15 piano gekocht voor 5000 nederlandse guldens.
we zijn tot nu toe nog steeds tevreden met de piano.
sinds een paar dagen wil hij niet meer hard spelen ,je hoort hem alleen nog maar in de verte .
alles is goed aangesloten ,schuifje staat op zijn hardst en er staat ook stroom op ,want het lichtje brand .
kan iemand mij vertellen wat ik daar aan kan doen ,ik wil hem nog niet kwijt ,misschien is het maar een kleinigheid.
mevr v haasteren
Posted on Sep 13, 2009
DO NOT REPLACE THE FUSE !!! You will do more damage.
I just repaired one of these. A small ceramic surface mounted cap very near where the +/- 85 volt connectors plug onto the board blew up.
This left a sputtered mess on the insulating material at the right rear corner of the power supply.
The net parts list of parts I had to replace:
1. Main IGBT transistors on heat sinks. You have to remove the heat sinks to get at the mounting screws. 1MBK50D or equivalent. I used DigKey part APT28GA60BD15
2. One 1N4148 surface mount diode that is for gate drive speedup. D24 and D25. (don't remember which one was shorted)
3. All four driver transistors for the gate of the IGBT's. @ each 2SA1020 (PNP) and 2SC2655 (NPN). These are tall TO92-like transistors and I believe that at least one of these I had to get from Mouser.
4. Transistor T9, suface mount BC856B (PNP)
5. Replaced all four surface mount caps, one had exploded.
C50, C51,C54,C56. Replace with 0.01mfd/200 Volt 1206 style surface mount caps Digikey 478-1511-6
6.Replaced ceramic wire wound 10 Watt stand up resistors that were blown open. Replaced with 20 ohm design change. These slowly charge the main input filter caps and when supply is stable, a relay shorts them out. If you have replaced the fuse, you LIKELY blew them out. Original value was 10 ohms on some units. This was a Mouser part. 280-PRM10-20-RC
7. The 2153 switching reg chip IC1. This chip shorts. It is made by International Rectifier and I believe the full number is something like IRF2153. I had these in stock and not sure of which source I had procured them from... It was from one or the other.
Lots of destruction and one really needs a desoldering station to work this. Removal of the blown IGBT's is especially tough. All solder must be removed from the transistor leads AND the thermistor on one of the heat sinks. Once you have verified the leads are loose, one has to rock the heat sinks to get the tabs free. The tabs are NOT soldered! Be careful when restoring to get the thermistor leads started in their holes.
Note: ALL these repair parts were procured from DigiKey.com and Mouser.com. Neither of these places had all, I had to order from both. Mouser had the ceramic resistors.
When restarting this, leave outputs disconnected until it is running again. USE a series 75 watt light bulb in the 120 volt input. ONLY work on the unit using an isolation transformer as a large portion of this is connected right to the power line.
There is a small 15 volt switching supply that comes on first that runs the relay to short out the inrush limiting resistors. With the 2153 shorted as usual, this auxilary supply can't reach voltage enough to turn on the relay. The power for this is supplied through the ceramic resistors.
Posted on May 08, 2010
SOURCE: my Korg c15s has a
I have a Korg C-15s and also experiencing loud crackling sounds when I turn it on. The problems seems to be either the sliding volume control or the amplifier itself. Honestly though, I believe the issue is the volume control. I opened my piano to get a closer look and attempted to clean the contacts on the volume. Unfortunately after cleaning the contacts, the crackling sounds became somewhat worse. After I turn the piano on, the volume control is generally rendered useless......volume set to low volume and the noise is quite loud and other times the volume control is set high and get very low volume crackling noise. No real consistency. The noise does diminish after a few minutes but so does the piano sounds to an inaudible level. There were a couple of instances where I turned it on and surprising enough, no no noise and perfect sound. For these reasons I believe the issue is within the volume control and not so much the amplifier. I have an electronics background and noticed that the volume control is very unique in design and is not something that can be substituted with another volume control from other sources.
My recommendation is to check the sound quality of the audio from the RCA L/R audio outs on rear of the piano by connecting to a stereo receiver. If it sounds fine you're in luck. If the crackling sound does not diminish after a few minutes like mine does, I would suggest disconnecting the internal speakers and using the audio out only. You can connect a pair of studio monitors or high quality computer speakers, preferably with a small subwoofer to deliver the full audio range and deeper tone of a real piano. I'm currently using a basic pair of Logitech computer speakers and is quite acceptable until I can afford a high quality set of monitors or relocate my piano closer to my high quality Yamaha receiver.
I hope this info helps a bit.
Posted on Aug 22, 2010
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