Korg EC150

Repair: Korg concert EC150

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ungefähr 6:47 Minuten

Lately I have had a Korg concert EC150 for service. This piano had one major issue, it was silent. Not even the slightest hum from the speakers nor on the headphones while the panel seemed to work just fine. So my first guess was this problem relates either to the power amp section or the corresponding power supply.

Sadly, there is no service manual nor schematics available on the internet for this digital piano so I thought it's a good idea to sum up what I came across. There is a good chance by the way that like with other digital piano series some of the information shared here may apply to all pianos of the EC series like EC100, EC120, EC300, EC310, EC320, EC350.

Disassembling the EC150

Open up the piano by removing three screws on the rear top, then slide back and lift the top cover. There are two PCBs mounted on a metal support standing upright in the piano, the power supply / amp board to the left and the mainboard to the right. Remove all screws keeping the support in place. Turn it by 90 degrees to make measuring easy.

Checking power

There are three voltage regulators in the circuit, a 7805 attached to a large heat sink serves for all mainboard and panel board operations while a KIA78R12 (TO-220 with 4 pins, on same heat sink) followed by another 7805 cater for the amp section.

The external power adapter (center positive) delivers 24 V / 2 A. On the amp board there is a 1N5404 diode right after the power switch connector to protect from wrong polarity on the small cost of a 1 V voltage drop. The rest of the power distribution is pretty straight forward.

Plugged in and switched on I measured 23 V on pin 1 (input) of two of the regulators but on the output side (pin 3 on 7805, pin 2 on KIA78R12) only the heatsink-7805 gave me 5 V while both of the other regulators had a poor 0,83 Volts. Too low voltage in case of power supplies can e.g. have the root in bad capacitors or a failing regulator itself, among others.

Since the Amp Mosfet IC (Tripath TP2050, accompanied by a TC2000 controller) has some protection embedded against over-current, over-/under-voltage and heat I guessed the faulty regulator(s) was the only issue.

Board repair

To get the board to the work desk remove all wiring by pulling off the connectors. The 5 pin connector in the board's center is of push down type, so press the collar down and pull up the flat cable easily. It's a good idea to mark both the right side of the connector and the rightmost wire (red) with a dot to prevent unwanted twisting before reassembling, see image.

Since most of the circuit is built on SMD technique and desoldering needs quite high temperatures and often a bit of leaded solder to bring down the melting point it was relieving there was enough reason to focus on some of the larger components first. Due to lack of schematics I did a quick sketch of the suspected area on the Korg KIP-2081 PCB, see image below.

EDIT: While trashing office papers I just found the quick sketch sheet again and decided to redraw this in KiCad, so here is the Korg EC150 PSU schematics PDF.

PDF Icon psu_korg_ec150.pdf (40.44 KB) (40.44 KB)

While all caps before and after the regulators where within specs and all diodes functional, two of the regulators were gone, 4-pin-78R12 and the 7805 (II) in chain, the one without a heat sink. If your EC150 suffers from the same symptoms it could be enough to replace the 12 V regulator since its output feeds the input of the 7805 (II). In my case this was not enough, unfortunately.

So after replacing both all voltages came back to specs and the piano was good to be played again.

By the way it's a good idea to replace the 6800µ and two 100µ caps before the regulators with versions for 35 or more volts since the input voltage from (a bad) power adapter might already exceed the original 25V, not to speak of normal cap tolerance.

Korg EC150 schematics

Note, the 12 V regulator's 4th pin is for enabling (high) and disabling (low). A blown heatsink-7805 (I) with no output would probably just switch it off.

Other issues and problems

Like many pianos of a certain age the EC150 had one key which could not be played soft. Instead, no matter how soft or strong you hit the key, the volume of the sound was always the highest possible. If your digital piano suffers from no dynamics or dead keys it's usually time to give the contacts beneath a cleaning. I described the procedure already here but for completeness, hey, once more.

Cleaning contacts of dead keys or keys with lost dynamics

The keybed is marked Fatar 1758, there are a variety of manufacturers using this for their digital pianos, even some chinese companies (sorry, probably to finally gain one star out of five in reviews). It's of good quality, the key mechanics is rock solid and the plastic does not tend to break or wear out. However, contacts catch some dust over time and start to fail, other than e.g. Yamaha keybeds that are more robust on this point. On the other hand I've had a lot of Yamahas with broken plastic.

Back to this one from Fatar. Remove the two keybed ribbon cables from the mainboard after you've marked them LEFT and RIGHT. Still, connecting them in the wrong order would do no harm except for the high notes appear on the lower keyboard and the low ones on the upper.

Remove the keybed's screws from underneath the piano. Note, three rear screws are a bit longer than the screws in the front. Lift up the keybed, turn it upside down and lay it on a desk or a piece of old carpet. Make a quick mark on the keybed PCBs where the metal support bars are. Then remove these bars. Remove all screws from the circuit boards and keep track of where which type of screw belongs. The wiring does not necessarily have to be removed.

Lift off the PCBs, turn them upside down and lay them on a desk. Remove the rubber contact mats and keep track of their position and orientation on the board. Be careful to get rid of all dust with a vacuum cleaner. Clean all contacts both on the boards and mats softly and properly with benzine or something comparable, make sure the liquid evaporates traceless. Use Q-tips or a soft cloth.

Korg EC150 key contact cleaning

Reassembling

Put the contact mats back in place and make sure they lay really really tight on the board. Don't make it easy for future dust armadas! To push the nipples through the corresponding holes you can use a small Allen key. Be careful and use something that is not sharp, otherwise you will cut holes in the mat. You could also use tweezers to pull the larger nipples from the other side.

Reassemble the piano in reverse order.

If you have any questions or additions, feel free to write a comment.

 

Comments/ Kommentare

#01

A big Thank You for posting this! I have one of these and 3 or 4 of my keys are really loud. As I could not find an engineer to come and have a look, your article is of great help. I am hoping with your guidance to be able to do it myself (actually my husband). I am thinking of changing the rubber contacts and not just cleaning, but Korg people did not advised proper on what to buy. Could you please be able to help?
They sent me two types of rubber contacts (with 12 way or 13 way). I think I should change them for all the piano (they might be wearing out anyway), but I don't know how many and which type to buy. Your help would be very much appreciated.
Thank you in advance for your help!

Best wishes,
Andreea Gheorghe

Hi Andreea,
just proceed as I decribed. There is very good chance that simple cleaning will revive all of your keys, I've done that on dozens of keybeds. Just make sure that after dust cleaning you use a solvent for the contacts that evaporates traceless, like isopropyl alcohol or special benzine (look on label). Do not use standard contact sprays like WD-40 as these try to "seal" surfaces which remains sticky for future dust.
If you really need to change the contact mats (which I doubt), there are usually mats with different sizes in one keybed, so it's best to place your order after you opened the keybed and counted the mats. If you have mats already there... they are usually marked with nipples in certain places, it's not possible to misplace them. Good luck!
Cheers
Ulf

#02

Moin...

...und vielen Dank für die tolle Anleitung zur Reparatur! Ich habe hier ein EC100h bei dem der Versuch zwei Tasten wieder zum Klingen zu bringen aber leider keine Besserung gebracht. Immerhin funktioniert nach dem Zusammenbau aber der Rest noch ;)

Woran kann es liegen wenn die Tasten trotz Reinigung nicht funktionieren? Gibt es eine Möglichkeit die Widerstände durchzumessen? Können die Kontakte irgendwie defekt sein?

Vielen Dank für jeglichen Hilfeversuch!

Gruß, Micha

Hallo Micha, danke für das Lob.

Tastaturen funktionieren meist nach dem Prinzip der Diodenmatrix – für jede Taste gibt es eine dedizierte Diode auf der Tastatur-Platine, in der Regel organisiert in 8er-Gruppen. Finde die beiden Dioden und miss nach. Miss auch nach, ob ein geschlossener Kontakt (Stück Alufolie statt Taste) überhaupt Durchgang erzeugt. Wenn kein Durchgang: Diode oder Leiterbahn unterbrochen.
Die Gummimatten hast Du bestimmt richtig eingesetzt gehabt? Tausch mal eine Matte und schau ob das Problem sich verlagert, denn das leitende Material auf den Köpfen in den Matten nutzt sich bei richtig intensivem Spiel auch mal ab.
Und dann weiß ich von manchem Synthesizer, das Tastaturplatinen manchmal Abstandhalter benötigen, die auch verloren gehen können (zb. Yamaha DX11). Ohne Abstandhalter neigt man dazu, beim Einbau die Platine zu fest anzuschrauben und die Tasten erzeugen keinen oder falschen Kontakt. Ob das hier auch der Fall ist erkenne ich auf meinen Fotos leider nicht.
Hilft das erstmal? Viel Erfolg!
Ulf

Moin!

Vielen Dank für die ausführliche Antwort!
Leider bin ich aber nicht am Ziel angekommen :(
Ich habe die Platine noch einmal ausgebaut und allein ohne den Rest der Tastatur noch einmal angeschlossen. Vorher reinigte ich die Platine und vor allem die entsprechenden Kontakte der Tasten gründlich. Und siehe da, es funktionierte! Und dann wieder nicht. Dann doch noch einmal, dann wieder nicht. Die Duoden hatte ich durchgelesen, das funktioniert. Ein Tausch der Gummimatte brachte auch nur wechselnden Erfolg. Liegt vielleicht ein schlechter Kontakt in der Platine vor? Hast Du da Erfahrungen?

Vielen Dank und Gruß, Micha

Hallo Micha,

ohne genauere Inspektion und zu messen hätte ich nun keine weitere Idee, außer dem offensichtlichen Wackelkontakt auf die Spur zu kommen. 2 Wege, beide bereits beschrieben: Nimm ein anderes Kontaktmedium und schließe aus, dass die Leiterbahnen kaputt sind. Oder schließe aus, dass es an der Kontaktmatte liegt. Da nur 2 Tasten betroffen sind ist ein Defekt in nachfolgender Elektronik sehr unwahrscheinlich. Der Hund liegt in der Tastatur(platine) begraben.

Viele Grüße
Ulf

#03

Hi Ulf,
I have a problem with an old EC120 which keyboard seems to be similar to EC150. All the keys are very noisy emitting a big click when I release them. Opening the keyboard, it seems that the little hammers under the key are falling on their support with a violent rebound when I release the key.
There's a little ribbon of rubber/silicon between the hammer and his support. Its function is to amortize the fall of the hammer and perhaps the solutions is to replace this ribbon but it looks fine.
So the keyboard is very less noisy when using it outside the piano. I think there's a big resonance when I fix the keyboard in the piano frame.
I have dissasembled all the keys with their springs, cleaned all from dust (no problem with the contacts) but the problem remains.
Would you have an idea that could help me to solve this?
I can send you pics or videos if you want;
Thank you and apologize for my poor english
Serge.

Salut Serge,
I understand your problem that seems to be a mechanical issue. I do not know how the keybed is built, unfortunately I did not take detailed keyboard mechanics pictures when I fixed the piano in this blog entry. So yes, sending me images is a good idea. I will send you my e-mail address and write the answer here just for completeness.
Pianos, digital/electrical or not, all make use of felt to make mechanics more silent. In digital pianos you often find one ore more long strips of felt underneath the keybed. This felt can get dented after intense use and as a result, hammer action is becoming noisy. Felt strips are replaceable, if a strip is dented a lot it's sometimes easier just to add a new layer to the old strip.
Good luck
Ulf

#04

Hallo,
ich habe ein KORG EC150. Von einem Tag zum anderen macht es nix mehr.
Netzteil gemessen = 21v. Wenn ich Power am Anschluss verbinde und während des messens die Power Taste drücke fällt die Spannung fast komplett ab.
Den 6800µ & 2x100µ erneuert, ohne Erfolg. Ein 78R12 ist profilaktisch schon bestellt, dauert aber noch bis der kommt.
Bitte um Rat / Hilfe bei Fehler Ermittelung. Finde leider auch keine Schaltungen für dieses Board.
Gruß Marc

Hallo Marc,
klingt nach Kurzschluss. An den Spannungsreglern bitte die Ein- und Ausgangsspannung gegen Ground messen. Wenn an einem die Spannung nicht stimmt, ausschalten und die 3-4 Pins auf Durchgang testen. Defekte Regler schließen oft kurz.
VG
Ulf

Hallo Ulf,
danke für den Tipp. Die Spannungen an allen Eingängen der Regler sind beim Einschalten gehn' Null. Mein Verdacht ist auch ein K-Schluss zu Masse. Die 2 "7805" habe ich zwischenzeitlich erneuert. An denen lag es wohl nicht. Ich werd den 78R12 mal auf Schluss messen. ---- Kein Schluss messbar im Eingebautem Zustand. ( Bei allen 3 ). Den 78R12 bau ich noch nicht aus für Messung, bis Ersatz da ist. Vorsichtshalber.

Hallo Ulf,
wie tel. besprochen, hier die Rückmeldung.: Die Fehlerquelle ist im ext. Schaltnetzteil (Typ: DSA-0421S-24 2 42). Dieser ist zum Glück noch verschraubt & nicht geklebt. Das Netzteil selbst ist sehr kompakt verbaut! Im Inneren ist ein grosser 100uF/400v, der auf der Unterseite "feucht" ist.
Das erklärt, warum die Out-Spannung noch ohne Last messbar ist /war!

Ich bedanke mich nochmals für Deine Unterstützung!

PS.: Das Netzteil braucht unbestromt "gefühlt ewig" bis es sich entlädt. (In der Schutzklasse ist kein PE!) Werde eine Netztrennung dazwischen setzen und ab dann, da abschalten.

Ich verbleibe mit bestem Gruss,
Marc Ashfield

Hallo Marc,
phantastisch! Den 100µF/400 hast Du hoffentlich gewechselt. Kondenswasser sollte sich da eigentlich nicht bilden, auch wenn das Netzteil glücklicherweise nur verschraubt war. Es kommt demnach auch Leckage in Betracht, die ja perspektivisch immer viel Schaden an Platinen anrichtet.
Viel und lange Freude beim Pianospielen jedenfalls!
Viele Grüße
Ulf

#05

Hi. I have this model, and its not working. When I press the power button, it start some popping sound and those small red lights are blinking. Can someone help me? Thanks

Hi Kristian,
get it to a service technician. This looks like a power issue. Most likely, any radio/tv tech can help you. Good luck!
Ulf

#06

Hello,
thank you for the detailed report. I have a EC310 which makes crackling noises sometimes when it's played. I opened the piano to try to find the error. It looks like it's "just" the right speaker. When I unplug the left speaker the sound is very quiet even with volume full on. When I keep one key pressed for some time it starts the crackling and after I release the key and play the volum is loud and it plays as normal. But sometimes I can hear some crackling. It looks like the voltage is dropping and afterward slowly ramping up. Before I started the measurement I thought I ask you if you have a tipp where I should start to search.

#07

Hallo und vielen Dank für die gute und ausführliche Beschreibung, sie hat mir sehr geholfen.
Mein EC150 hatte sich mit einem lauten Knacken verabschiedet. Ursache war letztlich ein defekter 12V Spannungsregler. Nun läuft alles wieder bestens!
Gruß Achim

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