Doepfer

Hi,

Sorry for the semi offtopic. I have a MS404 which has a problem with 
MIDI to CV conversion. The CV for the pitch and the VCF are only 0.5 
Volt per Octave instead of 1.0 Volt/Octave.

If there is someone who owns a MS404 and is technically enabled to do 
some measuring I would appreciate if he could check the voltages at pin 
12 of IC15 MAX 512 (=Reference voltage for the D/A-converter)
and the voltage at pin 7 of IC16 at different octaves.

Positions of the chips see http://fa.utfs.org/diy/ms404/ms404-1.jpg
Schematics see http://fa.utfs.org/diy/ms404/ms404-schematic-digital.jpg

At my MS404 the reference voltage mesaures around 2.53 Volt. The output 
of O23 (IC16) reads ~0.51 Volts/Octave.

Thank you very much for your help!

Florian

Florian,

2.53 V reference voltage are OK. With this reference you should measure
about 0...+2.5V CV at the output A of the MAX512 with 5 octaves jumps. O23
is used to double the CV output of the MAX512 (amplification ~ 2, adjustable
with trimming pot P26) to obtain the 0...5V CV range and 1V/oct. So probably
the DAC MAX512 is defective (if you do not measure 0...+2.5V) or O23 (if the
voltage is not doubled). Another reason could be a defective P26 or broken
R109 that causes O23 to work as a simple buffer (amplification 1).

Best wishes
Dieter Doepfer

> -----Ursprüngliche Nachricht-----
> Von: Doepfer_a100@yahoogroups.com
> [mailto:Doepfer_a100@yahoogroups.com]Im Auftrag von Florian Anwander
> Gesendet: Samstag, 13. Mai 2006 14:32
> An: Doepfer_a100@yahoogroups.com
> Betreff: [Doepfer_a100] Semi OT: technical help for MS404 needed
>
>
> Hi,
>
> Sorry for the semi offtopic. I have a MS404 which has a problem with
> MIDI to CV conversion. The CV for the pitch and the VCF are only 0.5
> Volt per Octave instead of 1.0 Volt/Octave.
>
> If there is someone who owns a MS404 and is technically enabled to do
> some measuring I would appreciate if he could check the voltages at pin
> 12 of IC15 MAX 512 (=Reference voltage for the D/A-converter)
> and the voltage at pin 7 of IC16 at different octaves.
>
> Positions of the chips see http://fa.utfs.org/diy/ms404/ms404-1.jpg
> Schematics see http://fa.utfs.org/diy/ms404/ms404-schematic-digital.jpg
>
> At my MS404 the reference voltage mesaures around 2.53 Volt. The output
> of O23 (IC16) reads ~0.51 Volts/Octave.
>
> Thank you very much for your help!
>
> Florian
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>

Hi Dieter

> the DAC MAX512 is defective (if you do not measure 0...+2.5V) 
The DAC measures 0..2.5 V at the output, so it is ok.


> voltage is not doubled). Another reason could be a defective P26 or broken
> R109 that causes O23 to work as a simple buffer (amplification 1).
Bonggg! I am blind. I should have thought about, that the trimmer or the 
resistors might be broken.

Thanks you for the hint.

Florian