Roland Alpha Juno 1 technical question

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Roland Alpha Juno 1 technical question

Postby del_amigo » Fri Feb 08, 2013 11:32 pm

Have an Alpha Juno One which I originally bought in 1985. Has not had much use. Just cleaned the key contacts because some keys were not playing. Reassembled, but some keys still not working. If I switch the instrument patch, say from elec piano to violins, keys that did not play start playing again, but a different set of keys stop! Weird..usually the keys are a tritone apart, like all the Es and all the B flats. If I change to another instrument, the Es and B flats work, but the C s and the F#s are all not working.

I did not touch the battery, and have never changed it. The keyboard has been sitting in storage for about 12 years.

Can you help?

Thank you,
Del
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Re: Roland Alpha Juno 1 technical question

Postby rhino » Sat Feb 09, 2013 12:06 am

Welcome to the board!

Sounds like some of the 6 voices are out. Let me take a look at the schematic.
Turn the synth off, then back on. Start at one end of the keyboard and play one key at a time and note the dead ones. Turn the synth off an on again - then withOUT playing a key, change to another patch. THEN play the same notes as before. If the same keys are dead, you've got bad voices.
"A thing may seem impossible...until it's done."
--Nelson Mandela
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Re: Roland Alpha Juno 1 technical question

Postby del_amigo » Sat Feb 09, 2013 3:18 am

Hi -

Did as you suggested, and you're right. The same dead notes were still dead. I then played six simultaneous notes, but only the first 5 sounded. The Juno 1 is a six- voice synth. Am I dead in the water, or can something be done?

Thank you for helping,

Del
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Re: Roland Alpha Juno 1 technical question

Postby rhino » Sat Feb 09, 2013 6:20 am

Almost no synth is beyond repair. Do you have electronic knowlege and tools? If not, it would be for the best to take it to a reputable repair tech.
Like most synths of that era, the juno has a rather standardized layout:
1) oscillators which make the note
2) filters which make the tone
3) voltage controled amplifiers that change the volume
4) various chips and circuits that send the control signals to the correct area.
Faults in any of these places can cause a voice to be silent - or otherwise incorrect.

Since 5 of the 6 voices work, it is unlikely that the problem lies in the micro-computer that runs it all.
It will take some testing to diagnose what has failed, and some skill to repair that fault(s).
"A thing may seem impossible...until it's done."
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Re: Roland Alpha Juno 1 technical question

Postby synthparts » Sat Feb 09, 2013 1:34 pm

In my experience with dead voices on Alpha Junos it is usually the IR3R05 VCF/VCA chip. You can try swapping the one in the deadd voice with one from another and see if it dead voice follows the chip. I have the chips in stock if you need one.
Vintage Synth Parts - http://www.synthparts.com
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Re: Roland Alpha Juno 1 technical question

Postby del_amigo » Sat Feb 09, 2013 8:17 pm

First of all, rhino, thank you very much for your help. You have given me a direction. I will have to find a reputable synth repair tech in the SF Bay Area. And, synthparts, if I understand your reply correctly, is there one chip for each voice and I have to somehow isolate the bad chip? Or does the chip you mention affect all the voices, so by replacing one chip I can possibly solve the problem.

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