KURZWEIL CUP2 No sound; LCD and buttons not working

[alexbez]

Hey guys, I am trying to diagnose what the issue is with my Kurzweil CUP2 digital Piano

The piano displays no sign of life besides a red on led.

• LCD screen does not display anything
• Buttons do not seem to do anything(there is a little red light above each button that indicates the "mode" it is in. Note, the button above the light should correspond with a button click. Not in terms of being in series, but in terms of the computer/engine board sending a signal to the light above the clicked button to indicate the mode of the piano)
• Audio In and Audio out on the rear panel do not work either. Note, the piano should have a audio passthrough feature that allows a external device to play audio through the piano's internal speakers and subwoofers.
• The USB MIDI passthrough is not recognized at all by windows

Sneaky suspicions

1. I think this could be due to the engine board not working since the engine board updates the LCD screen and LEDs above each button. Additionally, the Engine board controls the muting and unmuting of the speakers during startup and power down to prevent crackling. I think that the audio in at least is not working due to the fact that the Engine board is not doing anything to unmute the speakers in the first place. If I manually unmute the mute relay, would the piano work, or are the sound profiles and all that also controlled by storage on the engine board?
2. I want to try and reset the CPU and Engine board/even reload native OS, but the problem is that is all done through the interface of the buttons and LCD which do not power on!!!!

Notable details

1. The workings consist of four main PCBs as noted below:

1. No fuses are blown
2. The engine board receives power(10V) however the manual says that it should be 5V???
3. The LCD and Buttons on the control panel do receive power.
4. There are two LEDs on the engine board, but do not light up at any point?
5. All cables have been seated correctly and checked for continuity

I have absolutely no idea what the problem, and cause thereof could be.

All schematics required are mapped out here: https://elektrotanya.com/kurzweil_cup2_sm.pdf/download.html

Any help would really be appreciated

 

[happyrat1]

Probably leaky caps.

Buy an ESR meter and test.

 

[alexbez]

Probably leaky caps.

Buy an ESR meter and test.

Ok, perfect! Thanks for the suggestion!

I have also noticed that the full bridge rectifiers (D1 and D3) have a combined voltage of 86V(+-43V) and 52V(+-26V) respectively. The manual recommends it to be +-36 and +-24. Would this difference be significant enough to cause a fault??

Also, LEDs D1 and D2 are connected to the CPU, but never light up? This is despite there being nothing wrong with local voltages from regulators (3.3V and 5V). Could this mean that the CPU is blown, or that there is some signal preventing startup?

Thanks in advance!

 

[happyrat1]

The bridge voltages look close enough.

Possibly an internal short, maybe a fusible link has blown,

Prime suspect is the electrolytics.

ESR meter.

Every toolbox should have one.

BE VERY CAREFUL WITH SWITCHING SUPPLIES. 400+ volts in there.

Use a shorting probe on the caps.

Gary