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Waaaaaark
Joined: 26 Mar 2018 Posts: 3
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Posted: Mon Mar 26, 2018 9:24 pm Post subject: Korg X3 problem - seeking help |
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I just recently bought a used X3 from a less than reputable person and have since started going through it and fixing things. The biggest problem I've run into is that every C and F# in each octave doesn't trigger any sound. I got to the keybed and cleaned the contact and the rubber strip to no avail.
I would greatly appreciate any help. Thank you! |
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T3owner Senior Member
Joined: 17 Jun 2011 Posts: 368 Location: USA
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Posted: Tue Mar 27, 2018 9:33 am Post subject: Re: Korg X3 problem - seeking help |
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Since the problem affects all C and F# keys in every octave, it would be quite a coincidence if the cause was a key contact issue. Rather, there's a problem with decoding of the key matrix.
See https://en.wikipedia.org/wiki/Keyboard_matrix_circuit
Although more serious problems can occur, the typical cause is a poor cable connection between the keybed and the matrix decoding circuit. All it takes is a single bad conductor. _________________ Korg: T3EX, 05R/W | Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Fender Chroma Polaris | Roland U-220 | Etc. |
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Waaaaaark
Joined: 26 Mar 2018 Posts: 3
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Posted: Tue Apr 03, 2018 5:16 pm Post subject: |
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Thanks a lot for your help. It makes a lot of sense what you said about the key matrix. I checked all the wires going from the keybed to the main board for continuity and they all seem fine. Where should I go from here? Taking it to a shop is the last resort, honestly.
Again, thank you. |
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T3owner Senior Member
Joined: 17 Jun 2011 Posts: 368 Location: USA
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Posted: Wed Apr 04, 2018 3:52 pm Post subject: |
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You're welcome.
I presume you checked the 11-pin and 12-pin cables. Did you also verify that connectors are making good contact, and that the connector pins are properly soldered?
Based on the schematic I have, the C and F# keys share two lines. They are connected via CN3 (12-pin connector), pins 6 and 12. I suggest you trace the paths as far as you can on the boards at each end, even beyond where the cables themselves connect.
If nothing seems amiss there, then there may be a problem with a pullup resistor for one of those lines, or the key scanning processor (IC20, M37451M4) may be bad. _________________ Korg: T3EX, 05R/W | Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Fender Chroma Polaris | Roland U-220 | Etc. |
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Waaaaaark
Joined: 26 Mar 2018 Posts: 3
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Posted: Sat Apr 07, 2018 8:51 pm Post subject: |
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So I checked the connections on CN3 and found that on both ends everything is fine. I checked resistors R45-R79 that connect to CN3 and they all seemed to be fine, too. No damage that I could see to any components or traces anywhere. I'm just baffled at this point. I checked all the keybed diodes, too. |
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T3owner Senior Member
Joined: 17 Jun 2011 Posts: 368 Location: USA
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Posted: Mon Apr 09, 2018 2:58 pm Post subject: |
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Waaaaaark wrote: | So I checked the connections on CN3 and found that on both ends everything is fine. I checked resistors R45-R79 that connect to CN3 and they all seemed to be fine, too. No damage that I could see to any components or traces anywhere. I'm just baffled at this point. I checked all the keybed diodes, too. |
If the N01 and N10 lines are continuous from end to end (IC20 through the traces on the keyboard), and the pullups are OK, then the problem is likely IC20 related. Further troubleshooting could be done using an oscilloscope to compare signals on the suspect lines with ones where the keys function correctly. Look at the IC20 end of R52 and R63 versus others, with keys depressed and not. Even just a voltage reading might detect a stuck line. In fact, sometimes an ohmmeter reading to ground, comparing working and non-working lines, can reveal something. _________________ Korg: T3EX, 05R/W | Yamaha: Motif XF6 and XS6, A3000V2, A4000, YS200 | Fender Chroma Polaris | Roland U-220 | Etc. |
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