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From: etxbrfa@kklm01.ericsson.se (Bjoern Fahller)
Newsgroups: sci.electronics,rec.music.synth
Subject: TROUBLESOME OB-X
Message-ID: <1842@erix.ericsson.se>
Date: 21 Sep 88 06:28:56 GMT
Sender: news@erix.ericsson.se
Organization: Ericsson Telecom, Stockholm, Sweden
Lines: 39

Not very long ago, I bought a second hand Oberheim OB-X. I got it quite
cheap, because it sounded quite pourly. I didn't think of that as a problem,
because an electronics engineer should be able to fix such things. 
Unfortunately, it was much worse than I expected.
A few days later it was quite tuned though, but the filters were impossible
to tune to my ears satisfaction. The AUTO button, which I think is an auto
tuner, does not have the desired effect. Pressing the AUTO button, is the
absolutely best way of getting the synth detuned (and impossible to tune
again, unless powered down).
This isn't very good, ofcourse, but I could cope with it.
But a few days ago, something really bad happened. The four voices 5 to
8 is cronicly detuned. I don't think the error is on the voice cards, but
in some controller thats common for them. The situation now is the following:

Voices 1 to 4: Not correctly (the AUTO tuner) but sounds fairly good anyway.

Voice 5.   OSC 2   to low frequency. Can be tuned one octave down.
Voice 6.   OSC 1    -  II  -     -   II   --    --   II   --
Voice 7.   same as OSC 5
Voice 8.   The real looser.
           OSC 1   gives a ticking sound at about 3 to 4 hertz. The frequency
           is constant. (I think the OP-amp is killed, at least it gets
           very hot)

I have noticed, that the voltages on bus A is very different on the cards
5 to 8 compared with 1 to 4. Especially pin 1 on bus A on card 8. Its voltage
is constantly 15 V (the others are between -2.6 V and 0.5 V). I have tried
to swap the cirquits that is closest to bus A on voices 1 to 4 with the ones
on voices 5 to 8, but there was no change.

I hope someone can help me to save the synth, because analog synth's sounds
best and when it comes to analog synthesizers, Oberheim has the absolutely best
sound.

SNAIL: ERICSSON TELECOM         Vox humana: (+46) 8 - 719 62 52
       Bjoern Fahller
       KK/ETX/TT/MLG
       S-126 25 STOCKHOLM
       SWEDEN