VCF Cutof knob range problem.

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deejayraoul
 
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Joined: Wed Jun 03, 2015 12:14 am

VCF Cutof knob range problem.

Post by deejayraoul »

I posted this in the x0xb0x facebook group before, i hope to get some help here instead. My x0xb0x has been running fine for quite some time.
But now my cutoff pot seems to have its active range in the upper half of rotation. Below that i only hear the vca/envelope clicking.
The sound is otherwise fine. I've done some measuring and reflown most of the filter section to no avail. The components in the VCF section seem to be all fine (compared voltages with the posted reference file, checked voltage drop in for transistors in-circuit, checked 12V and 5,333V at jumper). I don't know about min/max voltages for the cutoff knob as they're not in the file. I could open up my 303 for reference, but i' a bit hesitant, hopefully someone here has a clue. I did notice both 50k pots (cutof, envelope mod) measured about 25k.
I might have damaged something while accidentally powering up with my yocto 18v AC psu, although everything seemed to be fine at the time. Any help is welcome.

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antto
 
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Re: VCF Cutof knob range problem.

Post by antto »

measure the voltage on the middle pin of the cutoff pot when it's set at minimum and at maximum
also check the voltage at D24 (on the side pointing towards R47) when the accent knob is at minimum

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deejayraoul
 
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Re: VCF Cutof knob range problem.

Post by deejayraoul »

I will have to remeasure tonight.
Cutof center went from about 4,6 to ~11 iirc. I'll get back with proper measurements.

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deejayraoul
 
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Re: VCF Cutof knob range problem.

Post by deejayraoul »

Cutof knob goes from 4,77 - 11,78. 3,2V at D24.

VerreyckenGerd
 
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Re: VCF Cutof knob range problem.

Post by VerreyckenGerd »

Maby a stupid question but have you tried the VCF calibration trimmer?

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deejayraoul
 
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Re: VCF Cutof knob range problem.

Post by deejayraoul »

Yes, i tried, the VCF trimmer doesn't change the range of the pot only the max value. I think maybe one of the regulating paired transistors is broken. They all seemed to show correct (not totally burned) testing them with diode measurements in cirquit. But they may be damaged, does anyone have a way to test those 5-pin paired transistors?

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