Juno 60 is missing one voice when VCA is set to Gate

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Yekuku
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Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Mon Nov 21, 2011 10:23 pm

Hi guys,
I am having an issue with a juno 60.
On the VCA section when Envelope mode is used all voices trigger as expected but if I switch to Gate mode then one voice is lost.
I suspect that maybe I am having issues with one of the envelope ICs (IR3R01) but I am puzzled because everything is working ok in envelope mode.
Any ideas ?
Thanks in advance.
Last edited by Yekuku on Thu Dec 08, 2011 11:40 pm, edited 1 time in total.
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by samuraipizzacat29 » Fri Nov 25, 2011 10:27 pm

this is the only service manual i could find:
http://www.4shared.com/document/aQVMQka ... anual.html

did you fire it up in the calibration mode, and if so, is there any "incongruencies" there. the only other thing I'd do is mess with all different kinds of envelopes and press down all six voices and see if you can get it to happen any other way (which it seems as if you've tried)

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Sun Nov 27, 2011 6:03 pm

Thanks for the reply buddy ;)
I run the diagnostic mode and it seems that voice No6 does not produce any output when VCA Gate mode is used.
In VCA Env mode all voices work as expected.
I checked Pin 6 on TP1 (Voice No6, Gate out) and I can confirm that the gate is working correctly.
Pin 6 on TP4 (Voice No6, VCA out) produces no reading when Gate mode is used. In Env mode pin 6 works as expected.
I am a bit lost because I can not understand how the "VCA Gate mode" works and which IC's are affiliated with this function. Is the IR3R01 IC (ENV) responsible for the VCA gate operation ?
Could a problem in a BA662 IC (VCA) trigger such a behaviour ?
Any ideas?

Here are the schematics of the mainboard:
Image

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by snod_donkey » Sun Nov 27, 2011 8:46 pm

chan 6 looks to be pin 11 of the ic for the gate at test point 1

Can you double check that? after that there is a couple of transistors that feed the vca..
Looks like there are 2 x 4011 for this so i imagine it will be ic 49


looks like the 4011 has a LOW output for the gate, this then triggers the ir3r01 and also the ba vca via transistors

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Sun Nov 27, 2011 11:37 pm

snod_donkey wrote:chan 6 looks to be pin 11 of the ic for the gate at test point 1

Can you double check that? after that there is a couple of transistors that feed the vca..
Looks like there are 2 x 4011 for this so i imagine it will be ic 49
You are right, Ch6 is connected to pin 11 of IC49 ;)

I checked all 6 channels at test point 1 and all of them produce the same drop in voltage when a key is pressed,( 5V->0.2V) which is normal operation.
I think the problem is beyond the ic49.
Any Ideas?
many thanks ;)
Last edited by Yekuku on Sun Nov 27, 2011 11:58 pm, edited 1 time in total.
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by snod_donkey » Sun Nov 27, 2011 11:57 pm

when you say you have tested at tp4 what are you doing? That point would be an audio signal as its the output from the vca i believe

After the 4011 it does a couple of things... it then turns pin 13 high on the ir3r01 through a transistor. Put your neg probe to 0v and check pin 13 goes high... if yes that that part SHOULD be ok

Then it also goes to tr7 / 8 so could be a duff tranny


Pin 1 of the ba662 is the control voltage input. What you should be getting is a voltage on pin 1 to turn the amp on.

Check a couple of pin 1's on others and se if they are high, you might find on voice 6 its staying low and not coming on. If thats the case its gonna be simple
Last edited by snod_donkey on Mon Nov 28, 2011 12:12 am, edited 1 time in total.

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Mon Nov 28, 2011 12:11 am

snod_donkey wrote:when you say you have tested at tp4 what are you doing? That point would be an audio signal as its the output from the vca i believe
Yes TP4 is VCA out so it is audio signal. I used a handheld oscilloscope and compared all 6 channels ; there were no readings on pin 6 (Ch6) when the VCA was set to Gate mode. In Env mode all pins of TP4 produced the same waveform.
I shall check and I will let u know.
Many thanks
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by snod_donkey » Mon Nov 28, 2011 12:15 am

Pin 1 of the ba662 is the control voltage input. What you should be getting is a voltage on pin 1 to turn the amp on.

Check a couple of pin 1's on others and se if they are high, you might find on voice 6 its staying low and not coming on. If thats the case its gonna be simple. might be tr7

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Tue Nov 29, 2011 12:14 am

It seems that there is a happy ending for this thread. Well sort of...
I used a multimeter and tried to compare readings of CH1 and CH6 in order to determine the fault.
In ENV section I checked R59,TR9,Pin 13 of IR301 and I got identical readings. This seemed logical because CH6 is working when VCA Env mode is used , that probably means that the gate input (pin13) of the IR3R01 (CH6 Env IC) is working correctly.
So i moved to the VCA section, checked R46,TR7 , TR6 and everything worked as expected.
I was about to check the BA662 but I quit out of frustration.
Then suddenly I noticed that ch6 was working again , that was why i was getting identical measurements on both channels. :facepalm:
Actually all I have done was to apply pressure to the above components in order to get my readings.
It seems that there is a bad contact probably on TR7 or TR6.
I ll check it out and I ll let you know about the results .

Thank you very much snod donkey, your support was very informative and it is much appreciated. :thumbleft:
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by snod_donkey » Tue Nov 29, 2011 11:13 am

No problem...

Might be a good idea to just solder up the transistors again to be on the safe side. At worst i think TR7 might want replacing but other than that looks like its all good and no expensive parts to replace

:)

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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Thu Dec 08, 2011 12:06 am

I have resoldered all the contacts that I have mentioned in my previous post and the problem seems to have gone away.
If it reappears I will consider replacing both TR7 and TR6 .
Anyways ,
I noticed that sometimes while editing a preset, the unit switches to manual mode by itself.
Interestingly I have found this :
Image
Does anybody know about this Juno 60 modification of wiring method ?
My Juno 60 has sn 317xxx, so there is need for this modification.
Unfortunately I cant find the attached drawing , so I dont know where exactly to connect these 2 wires.
Any ideas?
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by synthparts » Thu Dec 08, 2011 1:13 am

This must be the 3rd or 4th topic I've mentioned this in but yes if you are having he resetting problem you need to install new wires from the power supply to the panel board.
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Thu Dec 08, 2011 9:49 am

Sorry I have missed your previous posts, many thanks for the info.
As I understand I have to rewire the 5V and GND lines from the power supply to the panel board B.
Where exactly on panel board B do I have to connect these 2 wires?
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by synthparts » Thu Dec 08, 2011 1:19 pm

You can find +5 and Gnd at the connector next to IC10 (check service manual).
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Re: Juno 60 is missing one voice when VCA is set to Gate

Post by Yekuku » Thu Dec 08, 2011 11:39 pm

Many thanks, problem solved.:thumbsup:
I used 2 wires and connected the 5V & GND lines from the power supply board (orange and green wires) to the 5V & GND lines of the connector that is located to next to IC 10 (Panel board B)
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