KR-4500 Schematics

[Agent24]

Do you have an oscilloscope?

Put the piano into DAC test/calibrate mode and check the waveform. If it's messed up like the one I posted, you possibly have a DAC problem.

For me it was open circuit resistor in the adjustment pot circuit due to corrosion from the leaking capacitors. But with enough corrosion the DAC chips may also be damaged too. It could also be electrolyte residue causing leakage between tracks.

Carefully clean and check the DAC area for broken traces, vias, components.

Are the voltage regulators that power the DAC chips OK? If one rail is down the whole analogue output will be messed up.

[YvanJal]

I know this thread is very old but maybe someone will be able to help me.
My KR-4500 doesn't show any lights on and no characters on the LCD screen, but the screen is on (lighted) green but completely blank.
The CPU doesn't seem to be running. Does anyone have seen or heard about this problem before ?
Power supply voltages are good with a multimeter and with signal recorder.

I'm trying to find the complete service manual or service notes on internet but no luck.
Can someone help me find the problem and the manuals ?
Thanks

[Agent24]

I would check all power supply voltages and any secondary regulators. You could be missing a voltage rail.

Aside from that, it's possible that bad capacitors, a known problem, have corroded some traces in the CPU area and are preventing it from working.

The service manual was posted by someone else in this thread:

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

[YvanJal]

Thanks Agent24. I'm surprise getting an answer so fast !
I've replaced all the surface caps 10 microF on the board and tried to clean the corrosion but it still doesn't work. I'm starting to troubleshoot each IC to make sure all the supply voltages are present but I'm not sure which IC should be examine more carefully.
I've tried the site alex_2012 suggested but it's in Russian and I can't select the language. Maybe the site is not working anymore.
Thank again.

[Agent24]

The site should work, I just downloaded the manual myself.

First click this button:

1.jpg (27.05 KiB) Viewed 4132 times

You will get a dialogue to sign up. Just close that.

Then you will get this: Click the free download button:

2.jpg (43.03 KiB) Viewed 4132 times

I assume at least you would need the CPU, RAM and ROM to have power.

Corrosion if bad enough can go up into an IC through the leads and damage it, I have had this in the past repairing things. If an IC has corroded leads, it could be bad.
Also always be suspicious of any areas that have visible corrosion, verify continuity of any traces that look damaged, including vias.

Hopefully the schematic and PCB layout helps. You may wish to take the file to a print service and get the schematic, boards etc printed at A2/A1 size paper. Trying to look at them on the average monitor can be a pain.

[YvanJal]

Thanks very much Agent 24, I finally got the service notes from this site. I'm sorry I didn't reply before to let you know I was able to download it. Now i'm in the process of troubleshooting the board like you suggested.
Thanks again

[Agent24]

No problem, hope you can get somewhere with it!

I would say most likely you have a problem caused by corrosion, a broken trace or something, a failed solder joint due to corrosion, or a component that has corroded internally, or even a short somewhere due to uncleaned electrolyte.

Otherwise I can only think, assuming voltage is good, verify also any critical signal to the CPU. Does it have clock signal(s)? Is the reset signal working normally? (It may be held in the reset state by a faulty power-on reset signal generator circuit, or a short to ground on the reset line, for example).

Is the ROM OK? Also not held in reset? Are all address/data lines OK to the CPU and no shorts to ground/vcc?

[YvanJal]

I've already checked the reset voltage from the power supply. It's stable at 4.87V which should be ok. Now I'm in the process of checking all Vcc to the all the IC's. I've checked IC21 and IC54 and everything is OK. I'm expecting to receive by the end of april a Hantek scope which should help me a lot. Righ now I'm using an old strip chart recorder and, of course, a multimeter to troubleshoot the board. I cannot see the clocks. I have to figure out how to display them on my recorder. Thanks for your help Agent24. I really appreciate.

[upunkt]

Uploaded the Roland KR-4500 Service Notes to the wonderful and free Elektrotanya collection, since the russian site mentioned previously was blocked in my country (likely in other countries, too).

https://elektrotanya.com/roland_kr-4500 ... nload.html

[axolotl]

Hi all,

thanks for this informative thread!
I recently got a KR-4500. It has "digital buzzing sounds" on each key press which go away after a few minutes of warming up. Also, there was a fishy smell for a short period. I think that I have to replace the capacitors, so I did order the ones from page 2 of this thread (but from Nichicon).
Hopefully, the digital buzzing sounds will be fixed with the capacitor replacement and some good cleaning. :-)
Unfortunately, the service manual is no longer hosted at elektrotanya. Would you mind to upload it again or to another service, please? :-)