New Post-80017a Juno Troubles.

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Frayo
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New Post-80017a Juno Troubles.

Post by Frayo » Tue Oct 07, 2008 4:52 pm

I am not sure of some of the specifics of the Juno's architecture.

I was sold a Juno 106 off of ebay a while back with a dreaded 80017a dead voice.
The seller insisted that it worked perfectly. I guess it could have been a problem with shipping?

I have the solder and test equipment, as well as general electronics knowledge and experience. I installed the new chip, and soldered appropriate resisters to get the chip to calibrate. The chip worked fine (even though I had to recalibrate all the other chips to get them to work with the new chip)...but the resonance was weak.
Now the voice will not resonate at all, and I am not sure what I can do about it. I am not sure what components handle the resonance or what configuration they should be in. I have the technical manual and I tried adjusting the resonance pots that corresponded to the problematic voice.

I guess in summation: Does anyone know of a way I can get my fully working new voice to resonate (outside of the resonance woes, the chip works perfectly. Solder joints are not cold and are fine. The soldered resister bridge is in its proper place and works)

Any ideas?

I'm wanting to know so I can attempt to fix this thing before going out and getting a new Juno voice board.

Thank you for your time.

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Bross
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Re: New Post-80017a Juno Troubles.

Post by Bross » Tue Oct 07, 2008 6:29 pm

Which replacement chip did you use? What resistors are you refering to? I didn't think any replacement chip required adding resistors.

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cornutt
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Re: New Post-80017a Juno Troubles.

Post by cornutt » Tue Oct 07, 2008 7:10 pm

Frayo wrote: I installed the new chip, and soldered appropriate resisters to get the chip to calibrate.
I'm confused too. It should not have been necessary to change any resistors.
Now the voice will not resonate at all, and I am not sure what I can do about it. I am not sure what components handle the resonance or what configuration they should be in. I have the technical manual and I tried adjusting the resonance pots that corresponded to the problematic voice.
This doesnt sound good... the new 800017a may be blown. It may have gotten blown during your calibration attempts, or it may have been blown when you got it. Resonance is controlled by an OTA on the chip. There is a transistor that converts the reso CV to a current, which is fed into pin 2 of the 800017a. Between the voice's reso trim point and that transistor's emitter is a 27K resistor. Start by checking the voltage on the output side of the trim pot (between it and the 27K resistor) and compare to a good voice and see if they are about the same. If so, check the voltage on the other side of the 27K resistor, between it and the transistor, and again compare to a known good voice. That will tell you if the trim pot and the 27K resistor are good, and it might succeed in locating something like an emitter-base short in the transistor. If the trim pot and the resistor both measure good on an ohmmeter, maybe go ahead and change the transistor to see what happens. The other thing you might try is to (carefully!) re-heat the solder joint on pin 2 of the 800017a, just in case you got a cold joint on that pin. Also check the board around that pin for lifted or damaged traces.

Remind me which voice is bad, and I will look up the component designators for you.
Switches, knobs, buttons, LEDs, LCD screens, monitors, keys, mice, jacks, sockets. Now two joysticks!

Frayo
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Re: New Post-80017a Juno Troubles.

Post by Frayo » Tue Oct 07, 2008 7:47 pm

Thank you so much.
I did some searching and can't find it. The new chip included two resisters to solder in parallel to a resister already on the board if the tuning pots didn't calibrate it. They didn't and the chip was really loud...putting a resister in parallel with the other allowed me to use the trimpots to turn down the loudness of the chip.

According to http://www.analoguerenaissance.com/D80017/ this replacement was not very good.

The resonance did in fact disappear at lower frequencies in the beginning.

The voice was Voice 1. IC 13

Dang, I am not at home where I have the schematics.
I will check pin 2. I know how fragile semiconductors can be when soldering. I made sure to keep the soldering iron on there long enough to just melt and bind the solder and not heat up the chip (although some chips are less heat resistant than others).

I guess I should have fabricated a holder before soldering the chip, but I don't have the parts immediately available for that.

Thank you so much for the reply. I will test it this afternoon when I get home.

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