Roland Juno-D synthesizer gets stuck at startup.

Thread Starter

Yami

Joined Jan 18, 2016
227
Hi guys, I've got a roland Juno-D keyboard in for repair. What had happen was the owner went to turn on the keyboard and the front panel flashed on for a moment and the unit turned off with a burn smell.
Someone before me had a look at it and gave up. I have found the burned component which was the IR led (LED44) which is used for the D-beam. I checked all the components in its path and everything was okay. The tech who checked before me had removed IC8 which is an opamp. So I have replaced it with a new one.

What happens now
When the unit is turned on, the LCD lights up with dark block characters. No leds on the front panel lights up and the keyboard just gets stuck at startup. Sometimes the leds flickers on for a moment and then turns off.
I have checked all the power rails. The 5V and 3.3V rails are good. However the +9V rail shows 7.7V! and -9V rail shows -8.5V (which is in the limit stated on the inverter datasheet). There is no change with the 7.7V even when I disconnected all the other boards which needs the +9V.
I checked the crystals outputs and it shows clean sine waves. The things I check all seems to be ok, and I cant figure out what it could be. I thought that the microprocessors were not resetting on start up so I tried manually resetting it. No difference everything initializes and then gets stuck.

Potential breakthrough
I tired chasing the problem of the leds not coming on - I scoped IC6 which is a D-flip flop, the clock signal was there and all the inputs had square waves, but there were no outputs. A square wave does appear the moment the led flickers.
This is a problem right? But I still cant think why this could be a problem to cause the whole unit to freeze up.
I want to figure out what else could be causing this problem before ordering the flip flop.
Your help is greatly appreciated.
I have included the pdf of the service manual. The circuit diagrams starts from page 31.
 

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