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Subject: FW: [AH] PROBLEMS:OB-8

From: "Verschut, Ricardo" <Ricardo.Verschut@...
Date: 1999-12-13

-----Original Message-----
From: Luis Marka [mailto:mola@...]
Sent: Monday, December 13, 1999 3:22 PM
To: analogue@...; buzzardszun@...
Subject: Re: [AH] PROBLEMS:OB-8,JUPITER-8 and juno-106.

> Hello AH's...hope ye are all well.
> I have a few probs with my gear...any advice is welcome.
> 1)Around ten minutes after powering the synth up:Osillator 2 of the fourth
> voice drops in it cannot be hardly heard. Although...their is
> still some level...but not much...and it still works through the filter
> distortion at all...just very low level.???HELP???

Hmmm... this would require an oscilloscope and the schemos, one should
measure the signal from the VCO chip up to the mixing point. Questions
are: Does it happens in every waveform, or only in, say, sine or noise?
And does the envelope still "envelopes" fine? If this is the case, I
would bet in a VCA chip gone bad (BA662A, if my memory still works).

> 2)The white LFO mod button does NOT have any effect at all...either does
> it's relevant fader;s and and VCF LFO MOD,silver switches
> and faders and the LFO MOD RISE not do anything at all.....the
> pitch bender works fine on the VCO and the does all their
> silver switches and faders.
> The LFO works fine from the front panel of the synth..the rate and the
> and its destination ...all work fine...but NOT the WHITE LFO MODULATION
> BUTTON found in the bend box???HELP???

Check the button itself, then follow the presence/absence of signal up
to the LFO circuit. Schematics will make this job possible, its quite
hard to follow something inside a Jupi without them. Erm... is LFO MOD
RISE TIME turned full left?

> 1)similar to the jupiter voice problem!
> Around ten minutes after powering the machine on....VOICE 2 begins to
> crackle....and then their is NO SIGNAL at all from that voice..until the
> synth has cooled down.
> And on voice 4.....the same story with the time on powering the machine
> up....but the signal stays the same...NO DROP OF LEVEL at all.....but the
> CUT-OFF has NO EFFECT at all....although...when the RESONANCE is turned
> up.....RESONANCE IS APPLIED....the CUT-OFF does NOT?????HELP????
> This seems to be a thermal problem....yes...on the solder joins....or
> the VCO's and the VCF chips themselves???HELP???

VCF chips, without a doubt. If you ∗really∗ want to be sure, replace
these suspect chips with others that are known to work fine, eg. voice 1
<-> 2 and 3 <-> 4. If the problem "moves" to the other voices, bingo.
Oh, you�ll need to run the calibration procedures after replacing the
VCF chips.

Good luck, and greetings from Brazil,
Luis Marka