OBERHEIM SYNTH

Tried to send a message before but it seems to have been lost.

Picked up a used M6R with a couple bad voices.  Voice 2 was dead and just needed a re-seat of the CEM chip.

Voice 3 though - DCO 2 is all wonky.  Its pitch is way high and doesn't track correctly at all.  When changing the frequency through param 10 is generally trends in the right direction but any given value might be higher or lower than the one before.

I've probed around with a lousy scope a bit and it seems that pin 8 of the voice 3 CEM is at the wrong frequency.  i.e. I checked pin 4 and 8 of all the chips and only pin 8 of voice 3 seems to be at the wrong frequency.  As I said, it's a pretty lousy scope so info is limited.

Any thoughts on how to proceed?

Thanks in advance!

-Andy

hello

since it is a DCO the only possible fault should be the programmable 
interrupt timer 8254.

Florian


Am 04.11.2019 um 01:59 schrieb Andy Birko andy.birko@... [oberheim]:
> Tried to send a message before but it seems to have been lost.
>
> Picked up a used M6R with a couple bad voices. �Voice 2 was dead and 
> just needed a re-seat of the CEM chip.
>
> Voice 3 though - DCO 2 is all wonky. �Its pitch is way high and 
> doesn't track correctly at all. �When changing the frequency through 
> param 10 is generally trends in the right direction but any given 
> value might be higher or lower than the one before.
>
> I've probed around with a lousy scope a bit and it seems that pin 8 of 
> the voice 3 CEM is at the wrong frequency. �i.e. I checked pin 4 and 8 
> of all the chips and only pin 8 of voice 3 seems to be at the wrong 
> frequency. �As I said, it's a pretty lo usy scope so info is limited.
>
> Any thoughts on how to proceed?
>
> Thanks in advance!
>
> -Andy
> 


-- 
http://www.florian-anwander.de

I’m sure you’ve already done this but it’s worth saying just in case… before doing anything make sure you run the calibration. I’ve fixed many very extreme problems in my Matrix 6 and 1000 just by doing that.

 

Scott

From: oberheim@yahoogroups.com [mailto:oberheim@yahoogroups.com] 
Sent: November 5, 2019 7:48 AM
To: oberheim@yahoogroups.com
Subject: Re: [oberheim] M6R Help

 

  

It's CEM3396 which is a synth-on-a-chip; 2xDCOs, VCF, VCA, all in one. Pretty much the definition of a voice chip.

Individual clock inputs for the 2 DCOs. So if one DCO gets a bad clock input of course the pitch will be off.

 

On Tue, 5 Nov 2019 at 12:02, José Ángel Morente msxjam@... [oberheim] <oberheim@yahoogroups.com> wrote:

  

What CEMs are the wrong frequency?  Aren’t the M6 oscillators DCOs? 

 

If i’m not wrong, the CEM chips you talk about should be filters or maybe VCAs but no voice chips.

 

 

 

On Mon, 4 Nov 2019 at 23:38, Andy Birko andy.birko@... [oberheim] <oberheim@yahoogroups.com <mailto:oberheim@yahoogroups..com> > wrote:

  

Tried to send a message before but it seems to have been lost.





Picked up a used M6R with a couple bad voices.  Voice 2 was dead and just needed a re-seat of the CEM chip.

 

Voice 3 though - DCO 2 is all wonky.  Its pitch is way high and doesn't track correctly at all.  When changing the frequency through param 10 is generally trends in the right direction but any given value might be higher or lower than the one before.

 

I've probed around with a lousy scope a bit and it seems that pin 8 of the voice 3 CEM is at the wrong frequency.  i.e. I checked pin 4 and 8 of all the chips and only pin 8 of voice 3 seems to be at the wrong frequency.  As I said, it's a pretty lousy scope so info is limited.

 

Any thoughts on how to proceed?

 

Thanks in advance!

 

-Andy

Hi Jose

you were not wrong. The CEM3396 can not oscillator by itself.

And a DCO always consists from two components.
1.) a digital controlled divider (8253 or 8254) provides the clock
2.) a waveform shaper creates the waveform from that clock and a CV

In the M6 or M6R the clock is created by a 8254 and the wave form is 
shaped by the CEM3396

The official name of the CEM3396 in the Curtis Datasheet is "uP 
CONTROLLABLE DUAL WAVEFORM CONVERTER / PROCESSOR".


Florian

Am 05.11.2019 um 14:45 schrieb Jos� �ngel Morente msxjam@... 
[oberheim]:
> I was definitely wrong then; I always thought the CEM3396 had 
> waveshaping capabilities but it couldn't oscillate by itself.
>
> Thank you for the information.
>
> On Tue, Nov 5, 2019 at 2:16 PM Peter M�rck peter@... 
> <mailto:peter@...> [oberheim] <oberheim@yahoogroups.com 
> <mailto:oberheim@yahoogroups.com>> wrote:
>
>     It's CEM3396 which is a synth-on-a-chip; 2xDCOs, VCF, VCA, all in
>     one. Pretty much the definition of a voice chip.
>     Individual clock inputs for the 2 DCOs. So if one DCO gets a bad
>     clock input of course the pitch will be off.
>

-- 
http://www.florian-anwander.de