Hello everyone, I purchased for my experiments Roland Juno Gi, which periodically loses sound and sometimes distortion instead of sound. And sometime good sound.
USB-OUT
I tried connecting Juno-Gi to a Windows 10 computer and after installing the driver I was able to get sound from the Juno-Gi on my computer without distortion. Ok USB out is working, but I want to use it without Windows PC )
ELECTRICAL MEASUREMENTS
I took it apart, measured the power supply, and the first thing that came across to me as suspicious was the bipolar power supply with a large unbalance. Usually op amps are powered by a bipolar supply with the same voltage, for example +12 and -12, but in the Juno I found +6 and -8 across all supply pins of all op amps.
TERMAL TESTS
Next, I use a thermal camera and saw that one opamp was getting very hot, up to 60 degrees Celsius. This is usually quite high for low noise opamps. It was a LOW-NOISE DUAL OPERATIONAL AMPLIFIER JRC2068, which seems to be used for sound input and not used for output. I unsoldered it and turned on Juno without it. The power supply has almost leveled off, now I observed +7.5 and -8 in the power supply of all other opamps. But nothing has changed in sound quality.
CPU REBALLING
It continued to disappear and become distorted. It seems that the problem is in the R8A02021ABG sound processor, which I desoldered and installed on new balls with a diameter of 0.45mm. Nothing has changed either.
I wonder if this processor contains firmware inside it? Can I just replace it with a new one? I wrote to several companies that Google supposedly have it in stock, but have not yet received a response from any of them.
CONCLUSION
On the Internet I find many exactly the same problems with distortion with Roland, which are based on this processor. For example, BK-5 there is a service manual for it, I see that the only thing that unites everyone is the heart of the processor R8A02021ABG
I don’t see any point in buying used because there is a risk of simply buying the exact same dead one.
I need Service Notes for Roland Juno Gi.
Can anyone help me find a service manual?