oberheim ob-8 skipping voices

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oberheim ob-8 skipping voices

Postby radek tymecki » Thu May 01, 2014 9:05 pm

my ob-8 started acting very weird. it started skipping voice 4 and 5. sometimes it plays ok, but most of the time this issue appears. what can it be?
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Re: oberheim ob-8 skipping voices

Postby synthparts » Sat May 03, 2014 12:40 am

When you do an auto-tune do those voices pass or fail (patch number buttons 4 and 5 blink)?
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Re: oberheim ob-8 skipping voices

Postby radek tymecki » Sat May 03, 2014 10:34 am

yes. button 4 and 5 are lit. sometimes 3, 4 and 5
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Re: oberheim ob-8 skipping voices

Postby synthparts » Sat May 03, 2014 10:30 pm

I meant after the quick scan 1 to 8 does it then come back and blink 4 and 5 several times to indicate a tuning problem?
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Re: oberheim ob-8 skipping voices

Postby synthroom » Sat May 03, 2014 11:05 pm

synthparts wrote:I meant after the quick scan 1 to 8 does it then come back and blink 4 and 5 several times to indicate a tuning problem?


Does the OB-8 disable voices that fail tuning?
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Re: oberheim ob-8 skipping voices

Postby synthparts » Sun May 04, 2014 2:00 am

Yes it should.
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Re: oberheim ob-8 skipping voices

Postby radek tymecki » Sun May 04, 2014 9:19 am

yes. those voices are later disabled. but sometimes they pass the test and are in tune
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Re: oberheim ob-8 skipping voices

Postby Claudio » Sun May 04, 2014 1:07 pm

radek tymecki wrote:sometimes they pass the test and are in tune

Hi Radek,

I used to have same issues with my Expander until I recapped the PSU (excessive ripple on power lines).
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Re: oberheim ob-8 skipping voices

Postby radek tymecki » Sun May 04, 2014 2:50 pm

i've recapped all electrolytics except 1uf because i had none on stock [they come 3 per voice]
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Re: oberheim ob-8 skipping voices

Postby synthparts » Sun May 04, 2014 10:06 pm

Have you done the tuning procedure on those voices lately? The OB-8 has the about the easiest tuning calibration of any analog synth. It just consists of turning the trimmers until 2 LEDs light up... See the service manual.

If those voices still fail try swapping the CEM3340s to other voices and see if the problem follows them. If you need any CEMs I have them in stock.
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Re: oberheim ob-8 skipping voices

Postby radek tymecki » Wed May 07, 2014 9:11 am

i've noticed that one pin of small tape from midi interface is broken. i've repaired it, also checked all connections from midi to cpu board. now after powering up it makes me sth like this. btw - when i disconnect voiceboard and keyboard it's still same

https://www.youtube.com/watch?v=VJjjSAV ... e=youtu.be
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Re: oberheim ob-8 skipping voices

Postby radek tymecki » Sat Jun 14, 2014 7:06 pm

anyone? :(
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Re: oberheim ob-8 skipping voices

Postby Jacob Hunt » Sun Jun 15, 2014 7:09 am

My OB-Xa did this because of a bad chip in the s&h circuit for the autotune circuit, I believe it was a tl084. I don't know how similar they are, but the circuit was on the bottom right of the bottom board for my later era OB-Xa.
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