OBERHEIM SYNTH

Welcome to the group!!!

Have you tried sending CC 07 with a value of 127 to see if the midi volume is turned down all the way? A reset may cure this also.

After that I would start looking at the +/- 12 volts to make sure the analog section has enough good voltage to run. Does the volume pot affect the sound. If it fails the output will be missing. 

Then I would start following the circuit through to the 4053 mux. A simple audio input lead to a mixer with a 10k resistor can trace the audio path to see what is missing.

HTH, Fran

On Sunday, April 20, 2014 9:35 AM, "zc40@..." <zc40@hotmail.com> wrote:
  
  
>Hey guys great group, I like a lot. 
>
>
>I ask. 
>
>
>I have a 1000 matrix recently, 
>
>
>The ignition and all good, but the preset does not have sound, some preset sounds, but very low volume and bad. Believe that chips voices were good, I thought something in common, such as the 4053 ... but I'm not sure is the fault. 
>
>
>Thank you all. Greetings.  
> 
>
>

Do you have an actual audio signal through the potentiometer? If so work your way towards the output jack. U1, C4, etc. If not you can go back to U24 then the 4053 inputs and finally the output of the voice chips. Hopefully you will find audio somewhere along this path. Sorry to start in the middle.

You seem to have a good knowledge of testing and you have great test gear. Too bad we only have this barely readable print here in the files area. My old eyes are not very good with fuzzy schematics....

On Sunday, April 20, 2014 10:25 AM, "zc40@..." <zc40@...> wrote:
  
  
>Hello Narfman. 
>
>
>I tried regulators, 7912 & 7812. They look good, no voltage drop. The +5 & -5, also looks good. 
>
>
>I have an oscilloscope Tetronix & genreador signal and a voltmeter. evidence to go by. 
>
>
>The potentiometer output is fine. 
>
>
>From where you think you can do the first step?  
> 
>
>

Ok my bad. It is U2. The print must say U2A. A video would be nice.

It looks like the output of the 4053 should be pin 13. The input should be pin 14. This is more from the datasheet than the blurry schematic. If I had unlimited time I could rewrite the schematic. Fortunately I have a life. At least 25 percent has been playing lately. Love it! 

I enjoy helping. Glad to be of service. I'm in and out today since it's Easter and Mom has a big dinner planned. Mmmmm.  

On Sunday, April 20, 2014 2:13 PM, "zc40@..." <zc40@...> wrote:
  
  
>otherwise, I find u24, in the area near the top left corne, the U1, U2, U3, U4. but it is true that in the scheme puts u24 can be U2. ? 
>  I get confused?  
> 
>
>

I'm guessing you injected a signal into the DAC output and got a good loud signal at the output. Good job verifying the analog half of the circuit!!!
 
Does the DAC have digital inputs that are working? Do you have 500khz coming out of U607B? U617C toggles the DAC write line. The 82C54 timers U610 - U612 provide the initial frequencies for the voice chips. Are they running? There should be 8 bits on the data side of these timers. This data comes from the CPU.

On Tuesday, April 22, 2014 7:05 AM, "zc40@hotmail.com" <zc40@...> wrote:
  
  
>Hello, take long to respond. 
>  I've been looking, I saw how it works this part and is in good condition, For the voices, no sound. 
>  I have seen all of this is controlled by CV, I also did a test, remove the DAC (AM6012), and turned, and was loud. thus, I think the voices can be fine. I think that the problem may be within the control.  
> 
>
>

I'm not sure where TP12 is on the schematic. Check D703 and the two capacitors near it. This circuit generates the 5.6v. It is shown on page 12 of the schematic I have. Right in the center of the page. 

It could be that one of the 4051 chips is dragging down the 5.6v but more likely the problem is somewhere around the diode. The 5.6 volts is required for the CV to work properly. You are very close to finding the problem.

On Tuesday, May 6, 2014 8:01 PM, "zc40@..." <zc40@...> wrote:
  
  
>Hello, now I have another matrix unit that is correct, I've tried. or 801/3/4/9/10/11/12 and all is well ... The cpu also think it's good. 
>
>
>I see a strange thing. TP 12. voltage is 4.5 V ... 5.6 should not be?
>
>
>
>
>Thanks :)   
> 
>
>

One thing that I have seen happen before is a CMOS latch-up that pulls
down the +5.6 voltage which effectively destroys any voice control.
The CEM outputs seem to look good, though low, on a scope but you get
no audio output.  Then, when you test the +V of all the control CMOS
it is lower than +5.  Those chips latch up if they receive an input
voltage greater than the supply, which as it turns out, is how one of
the mux chips is wired.  The latch up sinks current and drags the
voltage down.  The unused input of that chip is tied to +5, and since
the 5.6 is derived from divider, the +5 gets there before the 5.6
rises fully.  I usually tie that input to ground and never have any
problems again.  You may need to replace the chip though if this is
the case as it may be damaged.

http://synthahol.tumblr.com/post/76933893079/oberheim-matrix-6-cmos-latch-up

On 5/7/14, Narfman96 - Narfland Studio <narfman96@...> wrote:
> I'm not sure where TP12 is on the schematic. Check D703 and the two
> capacitors near it. This circuit generates the 5.6v. It is shown on page
> 12 of the schematic I have. Right in the center of the page.
>
> It could be that one of the 4051 chips is dragging down the 5.6v but more
> likely the problem is somewhere around the diode. The 5.6 volts is required
> for the CV to work properly. You are very close to finding the problem.
> On Tuesday, May 6, 2014 8:01 PM, "zc40@hotmail.com" <zc40@...>
> wrote:
>
>
>>Hello, now I have another matrix unit that is correct, I've tried. or
>> 801/3/4/9/10/11/12 and all is well ... The cpu also think it's good.
>>
>>
>>I see a strange thing. TP 12. voltage is 4.5 V ... 5.6 should not be?
>>
>>
>>
>>
>>Thanks :)
>>
>>
>>


-- 
Patrick
Synth Tech @
http://www.switchedonaustin.com

Pull u711 and see if the voltage goes back up.

On 5/8/14, zc40@... <zc40@...> wrote:
> Hello, I have set up all the pin feeds all 4051 (I have actually cut pin 16)
> and have raised the whole 4053, is out of the motherboard (u710). I've also
> changed 7805 (U8)
>  taut is now good.
>
>
>  I took a voice and I put two and two ic sockets turned 4051, but when I put
> these new IC, the voltage back down.
>
>
>  One thing, before ic change u8 (7805), cut the output pin and I measured
> voltage tp12. and had 1.5 v …
>
>
>
>
>  Victor
>
>
>  :)
>
>
>
>


-- 
Patrick
Synth Tech @
http://www.switchedonaustin.com