So I have downloaded Service manual and checked the schematics. There's no PSU inside, just external power supply. But you can check voltages in power stabilizing circuit after U22, U23, U24, electrolytic capacitors around them, and there's also fuse - I would start with this one :-)LCD has here only 15 wires, modern displays in this HD44780 standard have 16. Here Cathode is on pin 15 (not 16), and probably Ground for backlight is common. But you have schematics as well, and experience with electronics and soldering, so you know all this.Contrast can be set on pin 3. Try to use different value for limiting resistor R3 to get voltage around or under 4 Volts.Daniel ForroOn Jan 19, 2015, at 2:53 AM, evang.paul@... [kawaisynths] wrote:Glad to see there are other out there with this little classic. I bought a K4 (not K4r) a few years back as a part of a bundle deal from a friend. It was in used but working order and it saw a couple years of use from me too, and all was well.
Then, I started building a Midi Controller following some plans online, and needed a 2x16 character LCD for the project. So, being cheap and crafty at the time, I said to myself, rather than buy one, why not just borrow the one from inside the K4. That worked out at the time.
Fast-forward approx 10 years, and I want to restore that K4 to its original glory and use it as a keyboard once again. Problem is, I can't find the original LCD or midi controller project anywhere...
So, a couple weeks ago I ordered the exact replacement off of eBay. While waiting for the replacement to come in, I opened the thing up and saw that the button-cell battery had leaked, so I replaced it (yes, i know, big no-no). Then, i received the LCD, made an improvised ribbon cable with an old IDE cable i had, and soldered one end to the LCD and connected the other end to the board following the 1:1 pinout i saw on the schematic i have.
Now, I turn the unit on, the LCD turns on/green backlight, however NOTHING else happens. No message at all on the display and, when connecting headphones to the audio outs, nothing is heard when keys are pressed.
I just read in the other LCD thread that, if the battery is removed while the unit's unplugged, this causes a loss of data. Now, is this what's affecting me, or is there a greater issue?
Any input would be greatly appreciated!!!!
Message
Re: [kawaisynths] Peculiar issue when restoring a K4
2015-01-19 by Leland Green
Hey, guys, I think we have a hacker here. :-)
(It's OK--I'm one, too.)
Disclaimer: I've never opened a Kawai synth, but I own a K4. I worked as a software engineer most of my adult life, and I have dabbled in electronics.
You ordered the replacement from eBay based on what? The part number on your schematic, or the characteristics of the LCD (e.g. 2 x 16 display)? If the latter, you need to use the former. Most, LCD's share the same pinouts, but not all. So if you just got a 2 x 16, it may be different. You need to make sure about this before proceeding.
You don't have an Arduino lying around, do you? If so, you could also hook up the LCD to it and run the demo programs included in the (Lady Ada) LCD library for Arduino.
Given you did all the above, I'd guess you did use the part number. So let's assume you have a correct LCD.
The only thing to do is go back and double check all connections. If you used an old cable, it might have broken wires. Just use your continuity tester/multi-meter to make sure your cable is good. If so, then connect one end, and test it from the end of the cable to the other side of the connection. In other words, you want to check the signal from the cable to the point it enters/exits the PCB. (Oh, yeah, with schematics you could probably do that with everything, but what would you have to remove to get to them all?) If that checks out, unplug, plug the other end in, and do the same test. If you can do these, meaning, if you can get to them to test. (You may need an "extension wire" on the contact leads from your continuity tester/multi-meter. To let you get into small spaces. I've seen these (older) cables get the pins deformed (in one way or another).
Another thing to check for is if there's any chance you un-soldered something else when you removed the LCD. That will be harder to track down, but using your schematic, you may be able to test everything around that area (if there was anything).
(I don't mean to sound pedantic, which my wife says that I do a lot. Ha!)
OK, so maybe that will help? If not, let me know if you have any questions I might be able to answer.
Good Luck,
Leland...
On Sun, Jan 18, 2015 at 9:24 PM, Daniel Forró danforcz@...m [kawaisynths] <kawaisynths@yahoogroups.com> wrote: