OBERHEIM SYNTH

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problem still there. I have now replaced all electrolytic caps but still same problem.

Any ideas?

---In oberheim@yahoogroups.com, wrote:

Maybe the DAC is faulty?

Show quoted textHide quoted text

From: jojoredhemp
To: oberheim@yahoogroups.com
Sent: Saturday, 8 June 2013, 20:17
Subject: [oberheim] Re: Xpander impossible to autotune!

Up! No ideas?

--- In oberheim@yahoogroups.com, "jojoredhemp"; wrote:
>
> Hi all,
> I have a xpander since some month and all was nearly fine. It began few month now with a dead voice, changed the VCO chip and since all good.
> But now since two week its impossible to tune the voices.
> When I use the autotune feature the result are random, sometimes all voice fail sometimes only 2 or 3 or more but never all pass. Even those who pass doesn't sound same.
> The PW test pass, RES pass, VCF fail, VCA pass.
> DAC monotonicity test fail I hear plenty of blips.
>
> I have equipment to repair it, I have learned electronic in school but the lack of description on how the cpu's works is a wall to me.
>
> If someone knows how the DAC monotonicity test is done perhaps that would help to locate the problem.
> I have done all calibration procedure and nothing wrong except the problems above.
>

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Hi John thanks for answer. When yo say : You need to look at the 5 volt supplies before and after the coil. If there's a lot of high frequency crap before the coil but not after, it's the filter cap. I've seen this symptom caused by this.

Can you pleae specifiy wich coil your refering too? I have the japanese version of the xpander wich is not the same power supply as the american one.

Also when I look at the signals like the Data and Adress lines around voice board processor they are far from rectangle signals, they look like sharp moutains. So it can maybe be a power suply problem. I have already repaired the power suply a year ago and worked fine. I did replace all electro caps and the switcher because he was fried.

I have found a cheap dac and did order it. Will swap it asap.

I will have a closer look at the 5v supply see if I can see something wrong with the scope.

---In oberheim@yahoogroups.com, wrote:

I would check the power supplies with a scope . You need to look at the 5 volt supplies before and after the coil. If there's a lot of high frequency crap before the coil but not after, it's the filter cap. I've seen this symptom caused by this. The other likely cause would be a bad DAC. If it has a bad lower bit, you couldn't tell by listening, but if you hear steps that don't correspond to half steps,when you change the oscillator pitch, either the DAC is bad or the fast-slow line could be bad.

Sent from my iPad

On Oct 10, 2013, at 11:21 AM, "joseph.redhemption@..." <joseph.redhemption@...> wrote:

problem still there. I have now replaced all electrolytic caps but still same problem.

Any ideas?

---In oberheim@yahoogroups.com, wrote:

Maybe the DAC is faulty?

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From: jojoredhemp
To: oberheim@yahoogroups.com
Sent: Saturday, 8 June 2013, 20:17
Subject: [oberheim] Re: Xpander impossible to autotune!

Up! No ideas?

--- In oberheim@yahoogroups.com, "jojoredhemp" wrote:
>
> Hi all,
> I have a xpander since some month and all was nearly fine. It began few month now with a dead voice, changed the VCO chip and since all good.
> But now since two week its impossible to tune the voices.
> When I use the autotune feature the result are random, sometimes all voice fail sometimes only 2 or 3 or more but never all pass. Even those who pass doesn't sound same.
> The PW test pass, RES pass, VCF fail, VCA pass.
> DAC monotonicity test fail I hear plenty of blips.
>
> I have equipment to repair it, I have learned electronic in school but the lack of description on how the cpu's works is a wall to me.
>
> If someone knows how the DAC monotonicity test is done perhaps that would help to locate the problem.
> I have done all calibration procedure and nothing wrong except the problems above.
>

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I have recieved the new dac, put into place, made calibration but still same problem.

I have attached scope picture of the 5V supply, U903_pin4 and U904_pin2 to show signals.

There is this kind of burst on the 5V supply.

The signal on U9 04_pin2 look awfull.

Any idea what could be wrong?

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Hi john, its a japanese one and problem is that the vco tuning fails. Its random never the same voice(s) fails. I cant remember wich other auto tuning like vcf, pwm,... fails but its written in my earlier posts.

Any idea?

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From: joseph.redhemption@... ;
To: ;
Subject: Re: [oberheim] RE: Xpander impossible to autotune!
Sent: Sun, Jan 19, 2014 12:47:09 PM

Hi Nick, with the DVM all is fine. But with scope you can see on the 5V supply some kind of burst. See my last post with attached scope shots.

Hi simone all the caps have already been replaced.