Summing Buss Help!!!

[OZ]

Hi All,


I am having nosie trouble with my trident 80 series console. I can no
longer wait for a tech here in Chicago. The problem I'm having is a
hum on the two buss. There is no equipment connected to the console
only speakers. With all modules removed the hum is eliminated and with
any one module re-inserted the hum re-appears. Also, on pin 2 on the
opamps(TL071,NE5534) socket on the Echo return module, there is a
-3.3v current present with the opamp removed from the socket.

By looking at the a schematic can anyone determine if voltage should
be present at pin 2 with no audio signal.

http://www.sandstorment.com/images/remix.jpg

Any help would be greatly appreciated.

Thanks in advance.

[OZ]

Thanks for your reply Mike. After digging through the console, it turned out
that there were some bad caps, chips, and a grounding issue. Thank god for
test equipment.

Again Thanks,

Ozzie
"Mike Turk" > wrote in message
. rogers.com...
> I would first check the power supply outputs for ripple.
>
> -mike
>
> "OZ" > wrote in message
> om...
> > Hi All,
> >
> >
> > I am having nosie trouble with my trident 80 series console. I can no
> > longer wait for a tech here in Chicago. The problem I'm having is a
> > hum on the two buss. There is no equipment connected to the console
> > only speakers. With all modules removed the hum is eliminated and with
> > any one module re-inserted the hum re-appears. Also, on pin 2 on the
> > opamps(TL071,NE5534) socket on the Echo return module, there is a
> > -3.3v current present with the opamp removed from the socket.
> >
> > By looking at the a schematic can anyone determine if voltage should
> > be present at pin 2 with no audio signal.
> >
> > http://www.sandstorment.com/images/remix.jpg
> >
> > Any help would be greatly appreciated.
> >
> > Thanks in advance.
>
>

[Pooh Bear]

OZ wrote:

> Hi All,
>
> I am having nosie trouble with my trident 80 series console. I can no
> longer wait for a tech here in Chicago. The problem I'm having is a
> hum on the two buss. There is no equipment connected to the console
> only speakers. With all modules removed the hum is eliminated and with
> any one module re-inserted the hum re-appears. Also, on pin 2 on the
> opamps(TL071,NE5534) socket on the Echo return module, there is a
> -3.3v current present with the opamp removed from the socket.
>
> By looking at the a schematic can anyone determine if voltage should
> be present at pin 2 with no audio signal.
>
> http://www.sandstorment.com/images/remix.jpg

Pin 3 ( non-inverting input ) is tied to ground, therefore feedback action
via R248 ? ( the number isn't clear ) should maintain Pin 2 also at ground
voltage - the classic virtual earth mix amp.

Suggest you check volts on Pin 3 too to check it has continuity to ground
- if socketed, there's a possibility that there may be a poor connection
due to ageing/vibration.

I see that more than one bus amp is affected - maybe the ground connection
is poor.

Graham