Electronic piano korg SP170 : dysfunction - Page 1
Forum section: electronics / repair

author: Poï
author_rank: Newbie
timestamp: February 03, 2025, 12:25:57 pm
content: "Hello everyone,I attached pictures of my keybord Korg SP 170.Some keys, on the very right side of the keyboard does not work properly or even not at all.Additionally some others works sometimes either with low or strong and sudden sound.What I've done:- cleaned the PCB with flux-off, the solder joint and the rubber band with IPA- tested the resistance: on the very right part of the plate there is a little black band printed that call for a test of 200 ohms (second picture). I've measured around 100 ohms on the tests points, which seems far from the theoretical value of 200 ohms isn't it ? What is the purpose of this resistor ?- observing plate: the first picture shows a place where the printed circuit board seems oxidized or maybe burned/damaged.It seems that changing the board that cost €60 wouldn't be silly, I found a German website with second hand spare part.Is there a way to be sure that the problem comes from the board ?Or any other remark or advice is welcome.Please let me know what you guys think.Thank you in advance for your help,Olivier"

author: jonovid
author_rank: Super Contributor
timestamp: February 03, 2025, 12:37:23 pm
content: corrosion on the printed circuit board

author: ledtester
author_rank: Super Contributor
timestamp: February 03, 2025, 02:05:03 pm
content: 1) Is this the service manual?https://www.manualslib.com/manual/1313552/Korg-Sp-170s.html2) Is the keyboard the RH-4? If so, I searched for RH-4 schematic and found this pic (also attached below):https://images.app.goo.gl/CMa6rezoAvNjosae8The keyboard seems to be divided into three sections, for instance, see this:https://www.keyboardkountry.com/korg-sp-170-middle-key-contact-board-klm-2950/#gallery-1and there seems to be one 16-pin chip per sections.Are the keys in an entire section not working? If so, it would suggest that the 16-pin chip in that section is not working.3) You might also want to try getting help from an online forum where people are discussing the repair of Korg keyboard instruments.

author: benj38
author_rank: Frequent Contributor
timestamp: February 03, 2025, 02:12:24 pm
content: No harm done, but you will probably attract more help if you move this topic to the "Repair" section of the forum.

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 03, 2025, 08:50:06 pm
content: These keys make contact with the help of the black pads in the white rubber strips. These pads should be conductive and make contact between the center of the key pad and either the back or the front bit. They probably measure key velocity based on the time between the two connections being made.Check if the black bits on top of the PCB are still in good condition and make proper connections when the black pads in the white rubber strip are pressed down on it.Best be careful with the black stuff because it may dissolve with aggressive cleaning agents.You can also test the functionality with two wires and make connections on the solder points at the back of the key row. You can follow the traces from the front center and back parts of the key pads.

author: Poï
author_rank: Newbie
timestamp: February 06, 2025, 06:30:10 am
content: Hello Benj38,well I'm trying to do so, but I don't know how to, without creating a new post in the repair section and deleting my post in the beginner section which will delete also the few interesting replies that i get, i guess.You may have an advice for this.Regards, Olivier

author: Poï
author_rank: Newbie
timestamp: February 06, 2025, 06:43:28 am
content: Hello Ledtester,My korg is sp170. I don't see any S at the end of it.I don't know what is RH-4 keyboard . According to your image I don't think it is.Regards, Olivier

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 06, 2025, 07:14:02 am
content: Quote from: Poï on February 06, 2025, 06:30:10 amThere should be a button at the end of the page with which you can move the topic. It is only there when you are the creator of the topic.I have not used it myself, so don't know what options it gives you when you press the button. As a normal user you are not allowed to delete a topic. Only administrators and moderators can do this.

author: EggertEnjoyer123
author_rank: Frequent Contributor
timestamp: February 06, 2025, 07:54:58 am
content: Your board has corroded traces, and you need to repair those first. I hope you wrote down all the keys which don't work, that will help you narrow your search significantly. Use a multimeter and check continuity between the black pad and the solder joints to verify.Once you fix all of the broken traces you can try shifting the group of keys that don't work a little when putting it back together. I fixed my friend's electric piano with the same issue by simply unscrewing and shifting that set of keys until the pads made reliable contact. It takes a few tries but generally you can get everything aligned well and it'll work. The reason why it plays soft/loud sounds is because the piano measures how hard you are pressing the key by checking the delay between when the first switch hits (which happens when you press the key down a little) and when the second switch hits. Both switches need to work for the piano to play the sound at the right volume.

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 06, 2025, 09:15:09 am
content: Check continuity between A and B and A and C and B and C. Be careful not to damage the black pads though.The bits on the PCB marked with the ellipse and rounded rectangle are suspicious, as is the trace marked with the red line.If there is no conductivity between A and C there is a cut in the trace going from A to the nearby center pads, and that would explain the not working keys.

author: Poï
author_rank: Newbie
timestamp: February 08, 2025, 10:26:24 am
content: Hello,Thank you all for your answers, giving me ideas and little understanding on how electronics works.Following PCprogrammer advices, i've checked A/B, A/C and B/C continuity for the first 25 keys starting at the right side of the keyboard.Continuity was ok everywhere except one key (overlined in blue on the first picture).Moreover I've tested resistance of the Black pads on the rubber strip: They are all around 3,2 kohms. I've tested also the resistance on each of the D*** component shown on the second picture: They are all around 3,7 Mohms. The third picture shows the place where I've tested 100 ohms between the 2 yellow points underlined with red arrows.Now severals keys are not responding ok. The more i work on it, cleaning, testing, checking, the less the keyboard is responding good.According to ledtester it could come from the 16 pin chip. Jonovid point on corrosion on the PCB, and I 've seen no continuity for one key between black pads and its solder joints. Well, I'm nearly ready to buy a new PCB to replace the whole section.But according to some research on the french internet, it seems that the problem could come from the contacts of the black pads on the PCB and rubber band. So I would like to try recreating it by adding some conductive graphite or carbon paint/spray. Well. Does my pads are made out of graphite or carbone (actually it might be the same thing) ? Is that option is a reliable solution ? Which product to buy to do it ? (source on the internet:https://www.satbuster.fr/electronique/reparations_touches_carbones_et_plastiques.html;https://fr.audiofanzine.com/les-mains-dans-le-cambouis/forums/t.737103,changement-des-contacts-en-caoutchouc-rubbers-sur-un-korg-sp-170s.html)Thanks in advance for your advices.Olivier

author: pcprogrammer
author_rank: Super Contributor
timestamp: February 08, 2025, 11:02:07 am
content: Good that you made a picture of the other side of the board. This shows it being a matrix scanning setup. Can you read the markings on the 16 pin IC and report it here, or provide a better picture of it.The fact that there is no conductivity between the pad and solder point you marked blue means that the trace is cut somewhere, and this might be hard to repair with the black pad stuff on the copper. I wonder what that is. Have not seen it before, but to be fair I have not worked on a musical instrument for a very long time.The corrosion on the board seems to be non destructive based on the result of your measurements.It looks to be 4 keys per scan line, and 8 read lines to capture the 8 pads of these 4 keys.Testing if there is a problem with the IC is probably simple. Just connect the scan line (marked with A in the picture) to the two solder pads next to it. This should make the note sound with maximum volume. Use a single blank piece of copper that you can push against the solder blobs to make instantaneous contact between the three solder blobs.You can try this for all the 24 scan combinations to test all the keys. If they all give sound the IC is fine and the problem is with the top rubber pads not making proper contact with the bottom pcb pads.

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 08, 2025, 01:13:57 pm
content: First, let me say that I have fixed both my Korg and Nord digital pianos with similar symptoms as yours, namely non-working keys or keys with incorrect sound volume. When such things happen, 99% of the time it is due to faulty rubber contact strips. In my case, both pianos needed work after about seven years of use.Three things generally happen with these strips: 1) the rubber has a small rip at the base of the carbon pedestals; 2) the carbon pads on the strips glaze over; 3) dirt/debris works its way under the rubber contact strips.In case #1, the strips must be replaced. In case #2, one can try cleaning the carbon pads on the strips. In case #3, you can remove the dirt/debris. However, in the latter two cases, the success may be questionable. Many people suggest cleaning things with alcohol; however many people say that alcohol can actually destroy the carbon pads on the strips and that nothing stronger than a little soapy water should be used. Hopefully, whatever cleaning you have already done hasn't further destroyed anything. I simply gently applied water on a Q-tip.You should be able to do the following: find an octave where the keys all work correctly, find an octave where they don't. Switch the two contact strips. If the fault follows the contact strips, you will know that the contact strip is bad. I would be surprised if it is a board or chip malfunction.If and when you decide to replace the contact strips (and you should replace all of them), take your time and do it correctly. Make sure everything is clean and dust free. The tricky part is setting the strips, as the rubber posts must be fully seated in the holes on the boards. When you are done, the strips should be perfectly level the whole way across. It took me about an hour on my Nord piano to get the strips all correctly seated.I bought my contact strips from Syntaur (here in the USA). Before you install them, look carefully at them. I spent hours disassembling and reassembling the piano with the new contact strips only to find that one key still didn't work. After I took it all apart, I looked at the carbon pads on the strip for that key. Sure enough, it was glazed (see the rightmost pad on the picture below). Syntaur did send me a new one.

author: Poï
author_rank: Newbie
timestamp: February 08, 2025, 02:04:11 pm
content: Hello Pcprogrammer,Well I've done the test you advised me to do. For each keys I got a sound, not always at maximum volume.I think I'm gonna change the rubber strip but before would like to know how effective it is to regenerate it with carbone paint or spray ? Does anyone have an experience of it ?Regards.

author: Poï
author_rank: Newbie
timestamp: February 08, 2025, 02:16:04 pm
content: Hello wn1fju,Thanks for sharing your experience. I've switched rubber strip from an octave to another. Result: some keys that were not sounding good before are sounding ok now , and vice versa.What about carbone paint ? useful or not ?Regards

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 08, 2025, 03:40:49 pm
content: Personally, I wouldn't bother with anything short of replacing the strips. It also depends on your budget and the relative cost to the value of the digital piano. It was about $100 USD to replace all the strips on my Nord, but that was worth it since the Nord was about $3,000 USD originally. I have no experience with the carbon paint, but I suppose you could try it (on the rubber contacts only, not the boards) because the worst you could do is end up having to replace the contact strips anyway.Generally speaking, I think once you start having problems with missing notes or improper sound volumes, the problem is only going to get worse over time with more and more keys going bad. Except for a few notes at the very top and very bottom of the keyboard, you are playing the rest regularly.In my Nord case, I started having problems with only one note (E-flat an octave above middle C). When I dissected everything, I found that the problem was more due to the rubber posts, on which the circular carbon pads sit, separating, not so much that things were dirty. I carefully examined all 88 notes and 31 of them were either separated or beginning to separate. And curiously, all the separated posts were at the same position among the three posts per note. The Nord uses a triple sensor mechanism, for better repeated key action, rather than dual sensors like on your Korg. Great - 50% more chances for them to fail!I really don't understand why almost all but the very, very expensive digital keyboards use these rubber contact strips. Well, actually I do understand - it must be cheap to manufacture. One would think an optical or capacitive sensor would last forever.

author: Poï
author_rank: Newbie
timestamp: February 08, 2025, 07:16:55 pm
content: After cleaning all the black pads on the rubber strip and on the PCB with cotton buds soaked in soapy water, and drying it right after, all my keys were responding better.Except one ! The one were i've checked no continuity yesterday. I've experimented something on it and it work not that bad. Tin wire welded on the solder joints at one end and touching the black pad at the other end. See the picture.I've order new rubber strip. 7 of them for the 7 octaves. 55 € with delivery, here:https://store.sonatek-group.fr/sav-korg/35475-ref-WKOC510500504102-2009000374713.html

author: lamoule74
author_rank: Contributor
timestamp: February 12, 2025, 09:58:56 am
content: Hey @Poi, your homonym fromFablab Perneshere,Good decision, I think.About your "experimentation", this is called a "strap", and next time could be also fixed it with some kind of copper tape like that :https://www.digikey.fr/fr/product-highlight/3/3m/copper-foil-tape-1181In this way, you can easily cut your track out like it was before being damaged.Also, after this, you can stabilize mechanically and protect electrically the new "conductive track" with some overcoat epoxy,https://www.oec.lintech.fr/p/kit-revetement-epoxy-cw2500/We've got that here at the workshop, it is a really helpful and convenient technique.

author: Poï
author_rank: Newbie
timestamp: February 14, 2025, 09:14:03 am
content: Hey @Lamoule74,thanks for your follow up.Interested in doing again the strap the way you advice, when you'll be back from snow.By the way, I've change the rubbers strips and keys response and sounding are way better now.Enjoy.