CAUTION: Please note that I do not take any responsibility or liability for any damage or mulfunction caused through this page. To modify or bend any circuits is all at your own risk.
1. 4x 16V/22μF capacitors (or volume) on main board's LCD Contrast part
2. 16V/10μF, 35V/4.7μF capacitors on DMF50202N LCD Module
Whoa, this is horrible.
notes: QY20, QY22, QY70, and QY100 use the same DMF50202N LCD module.
3. replace an internal battery
In advance, your data stored in QY20/22 must be saved externally by sending a SysEx.
QY20/22's internal battery should be replaced with a CR2032(3V) and a battery socket for it.
If you start QY after replacing battery, that will show "Illegal Input" and LCD display status or behavior will be unstable.
In such a case, you can turn on the power while pressing the following three keys simultaneously to clear all internal memory/factory reset: OCT DOWN + OCT UP + A#(Bb)
4. replace capacitors for repairing phones/line out
Tried to repair a QY20 with low audio output volume and noise. Since this was happening on both PHONE OUT and LINE OUT, my guess was that the problem was occurring in the circuitry prior to the volume slider.
Checking the circuit diagram in the QY20 service manual we can found on the internet, found that there are 16 electrolytic capacitors between the PCM69AP-2(DAC) and the volume slider: 16V/10μF x8, 50V/3.3μF x3, 16V/47μF x4, 16V/22μF x1.
It was not possible to tell which capacitors were leaking by looking at them, so I removed all of them. In this case, C37/C50/C60/C67 were leaking. These were indeed very difficult to remove.
Then I replaced these with new ones. Yes! The noise output is gone and the volume is back to normal.
notes 1: When removing the electrolytic capacitor, be very careful not to peel off the conductive sheet that is attached directly below the capacitor. It's very very difficult to reattach it once it is removed.
notes 2: Tips on how to remove capacitors
a. Suck out all the solder from + side.
b. Put the soldering iron on - side and shake the capacitor with tweezers to loosen the adhesive part little by little.
c. Put the soldering iron to + side again, and loosen it in the same way. When the conductive part can be shifted to the left or right, it is OK.
d. Put the soldering iron to - side again, and slowly remove the capacitor without rushing.