KR-4500 Schematics

Does anyone know if there's a place that has any contact pads for the KR-4500?

On mine everything works perfectly except about two keys in the same octave that need replacement contact pads.

Is there a place or person to obtain these from?

Hi ! This is a request for the schematics/service manual of the KR-4500.

I have recently been given an old KR4500 with the problem, decribed by "Foosy" in this blog and for which there seems to be no obvious solution - if repair is at all possible. It is not the crackling problem, which is apparently due to capacitor ESR.

Problem on my KR-4500:
· on start-up : message "No memory back-up > press Write"
· factory reset does not help.
· the piano sound is two octaves too low : I measured (FFT) exactly two octaves + slightly more than a half tone too low.
· the "Tune" and "Oct shift" buttons are always lit and can no more be controlled.
· pressing the "Tune button" displays : Master tune 4y3.5Hz (y is a garbled character)
· pressing the "Oct shift" button displays, what I think is rubbish, and can also not be controlled.
· Selecting other instruments gives about half of them two octaves too low, the other ones only approx. a half tone too low.
· In all cases, the MIDI output is the correct one : does not suffer from tone nor from octave shift syndrome. This means that the keyboard detection is functioning correctly.
· but: setting the MIDI local control off and connecting the MIDI out to MIDI in of the KR4500 does not change the tone and octave shifts. This means that the error is probably in the tone generation circuits.
· I could not yet generate a fully external MIDI input to see how the KR4500 responds to these commands but I really do not expect much change.
· ......

After removal of the shield above the main board, there is no obvious damage to the top nor to the bottom of the main board.

From the problems and the knowledge that, according to the previous owner, all problems occurred suddenly and together, I suspected the memory battery (or supercap) to be defective. Measuring the battery gave a voltage of 2.34Volt, which should be OK to keep the memory alive.
It also looks very strange to me that all problems would be caused by the battery only. I do not understand why this would cause a problem in the digital part, somewhere between the MIDI controller and the instrument generation. This is however very difficult to look at in more detail without schematics.

Therefore, I would ask if anyone on this forum has experience with the same type of problem and I would be very grateful if somebody could send me the schematics/service manual of the KR4500.
My direct email address is herman.casier@skynet.be

I will keep you informed if I manage to identify/cure the problem.
best regards,

for all, who needs service manual for KR4500, please download it from http://www.uloz.to/hledej?q=kr-4500 I check it it still there. Good luck. Alex

Hi all fellows pianists.

I know this thread is really old, but i just want to give a try and wish if there is someone here that could help me.


I have the kr 4500, with the common issue of the buzz, distorsion sound on it. I've changed all the mainboard caps (lot of them where leaked) and one of them has damaged a little but the board, only affecting one copper via. I've made a bridge and changed all capacitors.

The piano was working correctly for 3 days, and suddenly bang! again with the same issue. So all i can think off is something is overpowering the caps and sooner or later, those ones leaks.

anyone has a clue what may be causing this overpowering or continuos damage ? which parts could be causing this overpowering or whatever this is it ?
i guess it should come from mainboard, or may be could be the power supply ?

Thabk you in advance. i hope someone of you could help me.

I just got a KR-3500 with the capacitor issue, will be attempting a repair too. I can't say anything specific as I have not ordered the new capacitors or done any work\tests yet, but I would suggest some things:

1) Did you clean the old electrolyte off the board? If you leave it there, it could be conductive and cause problems. If you didn't - try the ideas here: http://www.badcaps.net/forum/showthread.php?t=8364&highlight=cleaning+electrolyte

2) Did you verify any corroded traces were really repaired? Check for corrosion in Vias\through-holes and clean them out and repair if needed. The board looks to be only 2-layer so it shouldn't be too difficult if you have some skill.

3) A PSU fault could cause problems, verify all the voltage rails are correct - do you have schematic? Also if you have an oscilloscope, check they are clean and free of ripple.

4) I found a page here: https://translate.google.co.nz/translate?sl=auto&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.daniloreale.it%2Fwordpress%2Felettronica%2Friparazioni%2Ftastiera-roland-kr-3500%2F&edit-text= which describes a repair to a KR-3500. There seems possibly a mention of re-adjusting the trimpots near the DAC chips - not sure what they do though - haven't seen a schematic for these.

For the record, I removed all the old capacitors, cleaned the board, installed new capacitors but still the left channel was bad with digital garbage noise. All voltage rails were all OK.

Viewing on the oscilloscope during the sine wave test for the DAC MSB calibration (VR1 and VR2) I could see the waveform was basically cut in half and totally out of alignment:[attachment: DSC00957_scaled.jpg] Tried to adjust this with VR1 but couldn't get the halves to line up. Compared all voltages on all pins of both DACs, everything matched except Pin 14 (MSB_ADJ) which was -2.637 volts on IC6 (left channel, bad) and -2.653 on IC7. Turning VR2 end to end showed the voltage for IC7 changing by almost 4mV but with VR1 IC6's voltage didn't move at all.

Turns out R3 (220K Ohm) was open circuit throwing the voltage divider out of whack meaning the MSB_ADJ voltage to Pin 14 of the left-channel DAC was ~13mV low and also couldn't be adjusted, and the DAC didn't like this. Replaced R3, recalibrated VR1 and VR2 and both channels work great.

If you still have problems, check that MSB_ADJ voltage on Pin 14 of the DACs. Seems it should be around -2.653v with respect to DGND and -2.623 with respect to AGND, and it should swing almost 4mV when you turn the VR1 or VR2 from end to end.

There have been a few of us with the following issues:

1. The notes are sounding an octave or two lower than they should be.
2. The “Tune" and "Oct shift" buttons are always lit and can not be turned off.
3. Pressing the "Tune" button shows: Master Tune 4y3.5Hz. This is not a 'y' but a garbled character.
4. Pressing "Oct shift" shows: Octave Shift B:_ 11_-2_11_2_11. Some of these are gibberish and pressing the inc/dec buttons do not change anything.

By the way, I have found that if I use the Utility button and turn GS mode on, the notes play in the proper octave, and not one or two lower like they do when the machine is first powered on.

Has anyone been able to solve all of these problems and get this thing running properly yet? Is it most likely a problem on the motherboard?

Unfortunately I have no experience with these, aside from repairing the one I mentioned, so I cannot say "oh sure, those problems are always caused by such-and-such going bad." for example, as is more often the case for example, in TV repair!

However.... since these obviously have a known capacitor issue, that would be the first thing to check.
Have the electrolytic capacitors on the main logic board been replaced and any electrolyte leakage cleaned from the board?
Next, check all voltage rails from the power supply: Are the voltages correct and the power is clean?

Dead decoupling capacitors for the digital ICs or out-of-spec voltages can cause digital circuitry to work incorrectly and may lead to this kind of issue. It's plausible that if all the units you mention have the same or similar power supply fault, it would affect the digital circuitry in much the same way.

The failure of one (or more) of the digital ICs or other components is also a possibility, a weakness in the design somewhere may mean a certain part always fails in the same way.

Ultimately though, without having yours in front of me I can only give general advice, and even that may be unhelpful if multiple people are seeing an identical issue, because then it's less likely to be a common electronics fault, and more likely something specific to these exact models.


A couple of other things spring to mind but neither of them seem likely:
Corrosion damage to PCB traces or IC leads etc from electrolyte leakage. This seems unlikely as corrosion will typically be random and with the same fault showing on multiple units, it doesn't add up.

Corruption of the data in the firmware EPROM due to old age is another thought, although again I expect that to be random and not result in the same issue across multiple units.

Hi Everyone,
On this post someone has given us all the capacitors that require replacing on the KR 4500. Now my question - PLEASE can someone tell me what capacitor goes where!! I have the schematic which does not say anything except for example C4. THats no help at all to me. THe orginal caps on my keybaord were changed by someone who replace everyone with same 10uf 25V electrolytic caps!

Any help or maybe a very hi res photo of someones intact board with cap readings on top of the tin caps.

Thanks

I can only speak for the KR3500...

10uF 25v is OK for most of them. Most are 10uF 16v and there are 4x 10uF 25v. With capacitors, you can use higher voltage rated ones as replacements so using a 25v rated one where a 16v one went is just fine. You can leave those ones in there.

However, there are 9 capacitors which are not 10uF at all. If those were changed for 10uF parts you may get problems.

C62 is a 1uF 50v part (to the right of CN2, the 15-pin connector that carries power from the PSU\Amp board)

Also, several of the capacitors around the DACs are 3.3uF 50v parts.

I have attached a file with the capacitor values and reference designators. You should be able to find them on the board silkscreen. Again, this is for the KR3500 so they may not be exact.

Let me know if you need photos, I can probably dig some up. But maybe it's worth it to get those from someone with a KR4500 in case there are some differences.

Thank you so much for this! You are a star!

Hi!
Have the same problem with my Roland KR-5500 digital piano. The capacitors are blown away and need to be replaced but I need a schematic to find out the right capacitors. Does someone have an idea where can I get a schematic?

Thanks a lot.
Viktor

You shouldn't need a schematic, the capacitors have their values printed on them. If you do want a schematic you could buy one here: http://www.manuals.altervista.org/Service/ServiceManual.html I bought the manual for my KR-3500 there.

Hi,
I have the same issue with my Roland KR-5500. The capacitors are blown and need to be replaced. So I'm looking for a Schematic for a KR-5500 and does someone knows the part numbers and where to order them.
Thanks for anything that can help me to fix that problem.

Thanks
Viktor

Hi All,

This thread is over ten years old now! I'm just tackling some problems with what was a very poorly KR-4500...

I replaced all the electrolytic caps on the main board and PSU/Amp board except one (awaiting its replacement). I also replaced a whole load of the switched on the right panel board - the sound presets, menu buttons were shot - bought a bag of 60 replacement switches for $5 on eBay.

Just a few issues remain...

The dreaded distortion sound when you play any keys. On mine, it sounds like a heavily-distorted electric guitar playing in sync! Does ANYONE have any idea what causes this?!!

Bender doesn't work. Cleaned and tested the pot, it word just fine. Anyone any ideas?

One key not working - hoping that's a simple fix once I get the keys out.

Given there are still a few of these pianos around, it would be good to revive this thread and help out any others facing similar problems.

Meanwhile, any tips would be massively appreciated!