Another Ob-Xa Issue

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Jacob Hunt
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Another Ob-Xa Issue

Post by Jacob Hunt » Thu Sep 26, 2013 7:32 am

Everything's going great until.. The top voice boards start to become horribly distorted. Autotune becomes useless. Somebody help me. Is this likely an OTA issue, or something more?
Last edited by Jacob Hunt on Fri Sep 27, 2013 11:51 pm, edited 1 time in total.

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Jacob Hunt
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Re: Another Ob-Xa Issue

Post by Jacob Hunt » Thu Sep 26, 2013 8:11 pm

Turns out the bottom boards also start to get crazy after the 3rd B key. They're not distorted badly like the top ones, but they sure don't sound right at all. Thanks in advance to anybody who may have some insight.

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Jacob Hunt
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Re: Another Ob-Xa Issue

Post by Jacob Hunt » Thu Sep 26, 2013 10:57 pm

It seems it is related to key CV maybe. Those notes' boards that go wacky are not getting past 3 volts for the key CV input when I go higher up the keyboard. Strangely though the top boards are getting proper voltage up until past 4 volts. The schematic has key cv as coming out of a 4051 (U47) on the lower board and running through a series of op-amps, which are simply just not in existance.. Maybe there's something after it that is the problem.

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Jacob Hunt
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Re: Another Ob-Xa Issue

Post by Jacob Hunt » Fri Sep 27, 2013 6:37 pm

Common sense prevailed, and I checked the voltage verification steps. IC #145 (another 4051) on the upper board is not recieving a proper 5.6v, but a not so healthy 2v. Now to track down the culprit(s).

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Jacob Hunt
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Re: Another Ob-Xa Issue

Post by Jacob Hunt » Fri Sep 27, 2013 8:12 pm

Turns out it was the 4051 itself. duh. Glad that's over with, I was getting pretty scared.

radek tymecki
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Re: Another Ob-Xa Issue

Post by radek tymecki » Fri Sep 27, 2013 9:58 pm

4051 is common failure in ob-xa. try to track down simple modification coz 5.6v is not proper voltage. i mean it is but it's factory mistake

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