new Euro Cota VCF - build debug time [solved]

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Pav
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new Euro Cota VCF - build debug time [solved]

Post by Pav » Wed Feb 05, 2020 12:35 pm

Hi,
Slapdash is back - this time for the Euro Cota

On first power up , I managed to short -12v rail to zero with a solder bridge on main board. :slapfight:
For testing i use a doepfer miniature power supply which has a 9v wall wart.
Coincidence or not ? I managed to destroy the wall wart - without damaging the power supply !

So I fixed solder bridge, and powered up again with a replacement wall wart, and tested the rails and
connectivity to the ICs ..and all looked ok power wise. Added pot board and plugged in an (Oakley) euro oscillator.

Expected to hear nothing - and got what i expected - nothing, nada. not even unfiltered output.
(I checked input attenuators were full CW.
So i followed the input path Filter In => CN3 pin 1 i have signal => R8 still ok => U2 where I try the output pins for a signal.

Here i hit the puzzle - if i touched pin 1 or pin 16 with the oscilloscope probe I get the signal path to -24db and -12b out socket.
I thought maybe a re flow of the pin but no output.
If I touch said pins with a wooden toothpick or similar to solder joint - no output.
If I touch with my finger - I get output :hmm: "Its an earthing problem" I concluded.

My question is - is this indicative of a damaged 13700 or should i continue to re flow surrounding resistors and capacitors that
go to ground around U2 ? Any suggestions.

Im still hoping one day - i will get an SMD module working first time.
Last edited by Pav on Sat Feb 08, 2020 9:46 am, edited 1 time in total.
rgds Pav

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Synthbuilder
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Re: new Euro Cota VCF - build debug time

Post by Synthbuilder » Wed Feb 05, 2020 4:44 pm

Sounds like the expo circuitry is not working. Pin 1 and pin 16 should be roughly at -11V and current is 'pushed' into the pins to change the centre frequency of the filter. The more current the higher the frequency. By placing a scope on there you are probably very softly pulling the pins down towards 0V (they won't move much from -11V) and this will engage the filter.

The problem probably lies around U1 or Q1 on the main board. Q1 could well be not soldered correctly.

Tony

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Pav
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Re: new Euro Cota VCF - build debug time

Post by Pav » Wed Feb 05, 2020 8:00 pm

I now suspect its Q1. Seems I ordered these from farnell without paying attention to the size...I just expected small.
Turns out the pads are for a SOT-457-6 which to be fair you mention early on in the build guide but i had ordered and put on a SOT-363.
So TWO reasons for it not working - pins not aligned to pads and dodgy soldering of the wrong component.

Testing will be put on hold until I reorder.
rgds Pav

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Pav
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Location: UK Hampshire

Re: new Euro Cota VCF - build debug solved

Post by Pav » Sat Feb 08, 2020 9:44 am

I replaced Q1 with the correct package size, and re flowed Q1 and I now have a working tested COTA filter. :tu:
I wondered whether Asymmetry had an issue but then with Soft Clip oscilloscope and ears showed it worked.
Is it correct it only works with soft clip on?
It only gets a brief mention in setup.
Maybe build guide should say a little more about Asymmetry as it is not a feature of 5U COTA,

Euro Envelope next.
rgds Pav

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Re: new Euro Cota VCF - build debug solved

Post by Synthbuilder » Sat Feb 08, 2020 10:01 am

Pav wrote:
Sat Feb 08, 2020 9:44 am
Is it correct it only works with soft clip on?
It only gets a brief mention in setup.
Maybe build guide should say a little more about Asymmetry as it is not a feature of 5U COTA...
Yes, the asymmetry control only works with soft clip engaged. It has no effect in the clean mode.

Normally this sort of thing would be described in the User Manual but I've not done one yet. It is mentioned on the project webpage though.

Tony

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