Doepfer

It's impossible to estimate from the distance what's wrong. I'd recommend to send in the module for repair if you have no experience
in electronics and soldering.

If you want to try the repair yourself: First of all I'd recommend to replace all integrated circuits. In most cases this solves the
problems. If this does not help I'd replace the transistors. If even this does not help the difficult part of the repair begins.

And please: turn off the system when you remove, install or swap modules !

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com [mailto:Doepfer_a100@yahoogroups.com]
> Gesendet: Dienstag, 9. Dezember 2014 01:07
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] A-108 Is 100% Silent
>
>
>
>
>
> Dear members,
>
> Technically I am so far with electronics, so I thought maybe you can help with this strange problem with my favorite filter A-108.
> I don't hear any any sound from the outputs, while the input is connected to the Saw of A-111; no click, no tick, no
> noise, just 100% silence, as if my whole setup is off. As if I'm on the top of Mount Everest.
>
> Some time ago, when replacing some modules, I touched a place on solder side near the Frequency potentio meter with the
> screwdriver, while the system was on. At once heavy agressive sparks rapidly appeared [not expected from such a 12V
> board], almost hit my face.
>
> The Frequency potentio meter was damaged and totally out of work. I only could change the frequency via the control
> voltage inputs. For the rest everything was fine.
>
> But since I took the damaged Frequency potentio meter out, I don't hear any sound anymore. It's 100% silence. The same
> after putting a new one.
>
> I did some measuring with these settings:
> With Sawtooth,
> A-111 Octave Switch at 0 (zero),
> A-108 Input Volume at 5,
> No CV's
>
>
> Results:
>
>
> From the power supply:
> -12V and +12V
> And the chips also get their power.
>
>
> From the input:
> DC = changing from -1V to +1V
> AC = 1.6V
>
>
> From CA3083Z: from IC4:
> pin1 (input) = 1V
> pin16 (input) = 1,5V
> pin15 (output) = 0,5V
>
>
> From TL084:
> All the inputs of their own circuits where equal. Sometimes the outputs where the same as their inputs.
>
>
> From BC 547:
> Q1 = 0,70
> Q2 = 0,69
>
>
> From the Outputs of the A-108: with DC measurement:
> 6db = 0,30V
> 12db = 0,15V
> 24db = 0,31V
> 48db = 0,06V
> BP = 0,09V
>
>
> From the Outputs of the A-108: with AC measurement:
> All Outputs = 0V
>
>
>
>
> ?
>
>
>
>

Thank you for the quick reply, Dieter.

Yes, I want to try the repair myself, for I have some experience
in electronics and soldering.

I'll follow your advice-steps, but if those do not solve the prob, I would rather buy another A-108.

So I'll let you know.

Oh yes, the thing about turning off the system when you remove, install or swap modules is, that sometimes you just want to check little things online (= system on) in between!

Or sometimes you think, that installing just one module would take only a minute and you will be extra carefully.

But now I have learn my lesson, for I experienced a pretty big force, when the sparks appeared. There also occurred a very small flame for a very short time. I could see it clearly, for it was in the evening with low light in the room.

When I remove the damaged potentio meter after some weeks, I saw the resistance-material inside it was greatly scorched.

> So, I finally have found it.
>
>
> First, I could not find new CA3083 chips to replace the suspected ones. They say, that they are not manufactured anymore,
> which could be a big problem, for a lot of modules use these.
>
>
> But than after a while, I came with the idea to use the suspected CA3083 chips on the A-143-9 QLFO.
> The results were, that all these chips were working fine on the QLFO.
> Than I replace the four suspected TL084 chips with new ones, and find out that two of them were broken. These two chips
> were the closest to the damaged potmeter.
>
>
> So, you got it right, Dieter.
> Thanks,
>
>
> Ben

I'm glad to hear that the faulty circuits could been discovered. But I'm wondering about your way to test the CA3083. The A-143-9
does not use a CA3083 !

Best wishes
Dieter Doepfer

Oh sorry, Dieter, I checked it and indeed it was not the A-143-9, but the A-120 LP Filter, which has two of them inside.

I don't know how I came to A-143-9; maybe I'm to busy with all kind of things, and the turbulence in the world nowadays.