Alpha Juno 2 Dead Voice (not voice chip)

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silviu
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Alpha Juno 2 Dead Voice (not voice chip)

Post by silviu » Wed Dec 24, 2014 10:36 pm

I have an Alpha Juno 2 that recently started having issues with voice 1. I traced that to voice A on the board and swapped the IR3R05 chips between voice A and B, and it made no difference. I think I can assume that the chip is not to blame. I am going to proceed with removing and testing all of the caps in voice A as I think that is the next logical step.

I wanted to check if anyone else had experienced a dead voice on an Alpha Juno or MKS-50 and if they could share any advice on what to test/where to look for issues. Thanks!

Ashe37
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Re: Alpha Juno 2 Dead Voice (not voice chip)

Post by Ashe37 » Thu Dec 25, 2014 1:56 am

is the VCA on the chip?

gslug
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Re: Alpha Juno 2 Dead Voice (not voice chip)

Post by gslug » Thu Dec 25, 2014 5:47 am

I haven't experienced a dead voice, but have spent some time poking around my MKS-50 with a scope in order to diagnose a noise problem. The IR3R05 is the only active component for an individual voice, but you seem to have eliminated that as the problem. There are a few electrolytic capacitors in the area that may be suspect, as well as trim pot VR1.

If you have access to a scope, check for a signal either side of C20, which couples the DCO output to the IR3R05. Also take a close look at the soldering - my MKS-50 had some awful dry joints.

silviu
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Re: Alpha Juno 2 Dead Voice (not voice chip)

Post by silviu » Sat Dec 27, 2014 12:35 am

Yes, the chip handles the VCF/VCA.

I've removed all of the capacitors to find out that my capacitance meter does not work. So I will just replace them, I have to head to the electronics shop today anyway. See what that does.

I will also test that trim pot, thanks for the suggestion.

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