Unit is probably 10-12 years old. I just recently noticed a buzz similar to
a ground loop and some computer chirping like sounds appear in my console on
the group faders.

Traced it back to the SPX-90.

All equipment is plugged into same power conditioner so traditional ground
loop is not likely, although one created by a failing spx-90 is possible I
guess.

It appears the SPX90 is buzzing and also is receiving radio transmission
from my DAW. If I disconnect all the audio connections, the buzz and
computer chirping noises in my console disappear (as you would expect).

By reconnecting the audio connections in this order.

1) input of spx-90 to send on console with ground lifted yeilds no noise
3) output of spx-90 to return on console with ground in place yeilds big
noises
3) lift the ground on the ouput of spx-90 to console, reduces noise but
still there.

So Im real sure the SPX-90 has an electronics problem probably easy for one
of you tech types to diagnose (leaky capacitor etc. etc. etc.)

How can I troubleshoot this with just a multimeter.

Thanks

Rob

You may have a problem with the power supply.
There's a plug and socket on the output of the power supply board which
should contain 5 volts for the digital stuff and +-15 (or possibly 18v) for
the audio. The PCB is marked. Measure the 5 volts. If it is less than 5
volts you most probably have leaky output caps. The preset is to adjust the
5 volts so you could try tweaking it to see if this solves the problem.
There are a about 6 electrolytics or so in total - the ones that usually go
are on the 5 volt rail itself, but you could just change them all. Don't
forget to adjust the preset afterwards, starting from full anticlockwise
before you turn on.

Gareth.








"Robert Stevens" wrote in message
. ..
Unit is probably 10-12 years old. I just recently noticed a buzz similar
to
a ground loop and some computer chirping like sounds appear in my console
on
the group faders.

Traced it back to the SPX-90.

All equipment is plugged into same power conditioner so traditional ground
loop is not likely, although one created by a failing spx-90 is possible I
guess.

It appears the SPX90 is buzzing and also is receiving radio transmission
from my DAW. If I disconnect all the audio connections, the buzz and
computer chirping noises in my console disappear (as you would expect).

By reconnecting the audio connections in this order.

1) input of spx-90 to send on console with ground lifted yeilds no noise
3) output of spx-90 to return on console with ground in place yeilds big
noises
3) lift the ground on the ouput of spx-90 to console, reduces noise but
still there.

So Im real sure the SPX-90 has an electronics problem probably easy for
one
of you tech types to diagnose (leaky capacitor etc. etc. etc.)

How can I troubleshoot this with just a multimeter.

Thanks

Rob

In article ,
"Robert Stevens" wrote:

Unit is probably 10-12 years old. I just recently noticed a buzz similar to
a ground loop and some computer chirping like sounds appear in my console on
the group faders.

Traced it back to the SPX-90.

All equipment is plugged into same power conditioner so traditional ground
loop is not likely, although one created by a failing spx-90 is possible I
guess.

It appears the SPX90 is buzzing and also is receiving radio transmission
from my DAW. If I disconnect all the audio connections, the buzz and
computer chirping noises in my console disappear (as you would expect).

By reconnecting the audio connections in this order.

1) input of spx-90 to send on console with ground lifted yeilds no noise
3) output of spx-90 to return on console with ground in place yeilds big
noises
3) lift the ground on the ouput of spx-90 to console, reduces noise but
still there.

So Im real sure the SPX-90 has an electronics problem probably easy for one
of you tech types to diagnose (leaky capacitor etc. etc. etc.)

How can I troubleshoot this with just a multimeter.

Thanks

Rob




A friends had a hum and I opened it and resoldered the ground wire to
the casing I think. Dry joint. Could be something along these lines...

Thanks for your suggestion. The strange thing is, if I test the ground
wire, it's has continuity. However, if I lift that saftey ground, all the
noises stop.

"David Morley" wrote in message
...
In article ,
"Robert Stevens" wrote:

Unit is probably 10-12 years old. I just recently noticed a buzz
similar to
a ground loop and some computer chirping like sounds appear in my
console on
the group faders.

Traced it back to the SPX-90.

All equipment is plugged into same power conditioner so traditional
ground
loop is not likely, although one created by a failing spx-90 is possible
I
guess.

It appears the SPX90 is buzzing and also is receiving radio transmission
from my DAW. If I disconnect all the audio connections, the buzz and
computer chirping noises in my console disappear (as you would expect).

By reconnecting the audio connections in this order.

1) input of spx-90 to send on console with ground lifted yeilds no noise
3) output of spx-90 to return on console with ground in place yeilds big
noises
3) lift the ground on the ouput of spx-90 to console, reduces noise but
still there.

So Im real sure the SPX-90 has an electronics problem probably easy for
one
of you tech types to diagnose (leaky capacitor etc. etc. etc.)

How can I troubleshoot this with just a multimeter.

Thanks

Rob




A friends had a hum and I opened it and resoldered the ground wire to
the casing I think. Dry joint. Could be something along these lines...

Thanks for your info.

I opened her up and put a multimeter across both the dc and ac connectors.

The DC was a little high (5.2v) so I backed off the pot to 5. I can't get a
good read on the AC lines. It's been years since I've known how to actually
read a multimeter so I'm thinking perhaps I have an RMS meter.

Anyway, the tweak did not help, but while inside I was testing the safety
ground connection too and noticed that if I disconnect it, the noise and hum
goes away completely. Obviously, I'm not gonna put it back together that
way, but what does that tell me?

Lots of caps, don't know which ones to monkey with. If I could isolate the
most likely suspect and replace it, that would be a could start I suppose.

Thanks for your past and any future help.

Rob



"Gareth Magennis" wrote in message
. ..
You may have a problem with the power supply.
There's a plug and socket on the output of the power supply board which
should contain 5 volts for the digital stuff and +-15 (or possibly 18v)
for
the audio. The PCB is marked. Measure the 5 volts. If it is less than 5
volts you most probably have leaky output caps. The preset is to adjust
the
5 volts so you could try tweaking it to see if this solves the problem.
There are a about 6 electrolytics or so in total - the ones that usually
go
are on the 5 volt rail itself, but you could just change them all. Don't
forget to adjust the preset afterwards, starting from full anticlockwise
before you turn on.

Gareth.








"Robert Stevens" wrote in message
. ..
Unit is probably 10-12 years old. I just recently noticed a buzz
similar
to
a ground loop and some computer chirping like sounds appear in my
console
on
the group faders.

Traced it back to the SPX-90.

All equipment is plugged into same power conditioner so traditional
ground
loop is not likely, although one created by a failing spx-90 is possible
I
guess.

It appears the SPX90 is buzzing and also is receiving radio transmission
from my DAW. If I disconnect all the audio connections, the buzz and
computer chirping noises in my console disappear (as you would expect).

By reconnecting the audio connections in this order.

1) input of spx-90 to send on console with ground lifted yeilds no noise
3) output of spx-90 to return on console with ground in place yeilds big
noises
3) lift the ground on the ouput of spx-90 to console, reduces noise but
still there.

So Im real sure the SPX-90 has an electronics problem probably easy for
one
of you tech types to diagnose (leaky capacitor etc. etc. etc.)

How can I troubleshoot this with just a multimeter.

Thanks

Rob

Lots of caps, don't know which ones to monkey with. If I could isolate
the
most likely suspect and replace it, that would be a could start I suppose.

Thanks for your past and any future help.


Looks like an earthing problem, which can be horrible.

Make absolutely sure again it is not your wiring!! (Use different cables,
forget the multimeter)

The main pcb earths to the chassis via a screw in the corner and possibly
via the jack nuts on the back. You could try making sure these are clean and
tight..

I've had problems before with units that dont like having their chassis
connected to other units via racks. (you can buy insulating spacers).

Good luck.

Robert Stevens wrote:
Thanks for your suggestion. The strange thing is, if I test the ground
wire, it's has continuity. However, if I lift that saftey ground, all the
noises stop.

This is not strange, this is how ground loops work. There is a nice
discussion of this in the FAQ.

Do not lift the safety ground. Lift a signal ground instead.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Yes, I grounded the chassis with the saftey ground lifted and verified that
the buzz does come back as you suspected.

Something is definitely amiss inside this puppy. I did replace the cap
across the +5dc rail, it was simple, but the rest of the caps are much
tighter and I'm afraid not worth the effort.

Anyway, thanks for your help, I reconnected the safety ground and put the
unit in my practice PA where the buzz won't be so critical.

Can you elaborate on what an "Earthing Problem" is?

Thanks

Rob

"Gareth Magennis" wrote in message
. ..
Lots of caps, don't know which ones to monkey with. If I could isolate
the
most likely suspect and replace it, that would be a could start I
suppose.

Thanks for your past and any future help.


Looks like an earthing problem, which can be horrible.

Make absolutely sure again it is not your wiring!! (Use different cables,
forget the multimeter)

The main pcb earths to the chassis via a screw in the corner and possibly
via the jack nuts on the back. You could try making sure these are clean
and
tight..

I've had problems before with units that dont like having their chassis
connected to other units via racks. (you can buy insulating spacers).

Good luck.

Robert Stevens wrote:
I'm quite familiar with ground loops. This may or may not be the case, but
I believe something inside this particular unit is failing causing the
"ground loop".

Lifting signal ground does not help. The only thing that stops the buzz and
computer chirping is making sure the chassis is not grounded either through
the saftey ground or by touching another ground chassis.

Is the signal ground really a signal ground? Are the inputs and outputs
really balanced?

I did replace the electrolyte cap across the +5dc but that did not help any.
Not that interested in recapping the whole unit.

That won't do anything. You have a grounding problem. The thing is that
pseudobalanced and "impedance balanced" connections can make simple grounding
problems into more complex ones.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

The unit is certainly not "Transformer Balanced". The board isn't either.
The board I can confirm is Servo Balanced and the FX unit definitely has
some sort of balancing circuit inside it and a switch to switch between
+4dbu and -20dbv.

Problem exists in either switch position.

Connecting the input audio cable does not introduce the ground loop.
Connecting either output audio cable does introduce the loop assuming that
the unit is earthed. Unearthed, there is no buzz with everything plugged
in.

Again, I'm sure everything is plugged into the same power conditioner but as
a test I unplugged all the other units except for the FX and console and
used headphones to verify the buzz still exists. Results are the same,
earthed buzz, unearthed, no buzz.

Standard TRS with ground in tact on or lifted, makes no matter. Earthing
the unit and hooking up one of the output audio connections makes it buzz.

"Scott Dorsey" wrote in message
...
Robert Stevens wrote:
I'm quite familiar with ground loops. This may or may not be the case,
but
I believe something inside this particular unit is failing causing the
"ground loop".

Lifting signal ground does not help. The only thing that stops the buzz
and
computer chirping is making sure the chassis is not grounded either
through
the saftey ground or by touching another ground chassis.

Is the signal ground really a signal ground? Are the inputs and outputs
really balanced?

I did replace the electrolyte cap across the +5dc but that did not help
any.
Not that interested in recapping the whole unit.

That won't do anything. You have a grounding problem. The thing is that
pseudobalanced and "impedance balanced" connections can make simple
grounding
problems into more complex ones.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Robert Stevens wrote:
The unit is certainly not "Transformer Balanced". The board isn't either.
The board I can confirm is Servo Balanced and the FX unit definitely has
some sort of balancing circuit inside it and a switch to switch between
+4dbu and -20dbv.

Is it really servo balanced? Find out... disconnect pin 2 and then disconnect
pin 3. With one wire in place, you should still have signal. If you don't,
then you don't have real servo balanced inputs and outputs.

Problem exists in either switch position.

Right, it has nothing to do with operating level.

Connecting the input audio cable does not introduce the ground loop.
Connecting either output audio cable does introduce the loop assuming that
the unit is earthed. Unearthed, there is no buzz with everything plugged
in.

Right, makes sense. But when you plug the input in, it buzzes, right?

Again, I'm sure everything is plugged into the same power conditioner but as
a test I unplugged all the other units except for the FX and console and
used headphones to verify the buzz still exists. Results are the same,
earthed buzz, unearthed, no buzz.

Standard TRS with ground in tact on or lifted, makes no matter. Earthing
the unit and hooking up one of the output audio connections makes it buzz.

Sit down and draw it all out. You won't find problems like this by trial
and error. You may find that you will need to add a transformer.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Right, makes sense. But when you plug the input in, it buzzes, right?

Actually no, the input audio connection does not introduce the buzz, only
the output audio connections.





"Scott Dorsey" wrote in message
...
Robert Stevens wrote:
The unit is certainly not "Transformer Balanced". The board isn't
either.
The board I can confirm is Servo Balanced and the FX unit definitely has
some sort of balancing circuit inside it and a switch to switch between
+4dbu and -20dbv.

Is it really servo balanced? Find out... disconnect pin 2 and then
disconnect
pin 3. With one wire in place, you should still have signal. If you
don't,
then you don't have real servo balanced inputs and outputs.

Problem exists in either switch position.

Right, it has nothing to do with operating level.

Connecting the input audio cable does not introduce the ground loop.
Connecting either output audio cable does introduce the loop assuming
that
the unit is earthed. Unearthed, there is no buzz with everything plugged
in.

Right, makes sense. But when you plug the input in, it buzzes, right?

Again, I'm sure everything is plugged into the same power conditioner but
as
a test I unplugged all the other units except for the FX and console and
used headphones to verify the buzz still exists. Results are the same,
earthed buzz, unearthed, no buzz.

Standard TRS with ground in tact on or lifted, makes no matter. Earthing
the unit and hooking up one of the output audio connections makes it
buzz.

Sit down and draw it all out. You won't find problems like this by trial
and error. You may find that you will need to add a transformer.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article ,
Robert Stevens wrote:
Right, makes sense. But when you plug the input in, it buzzes, right?

Actually no, the input audio connection does not introduce the buzz, only
the output audio connections.

Okay, now how is the output on the SPX90 balanced and is it really balanced
at all? Does the console have a real differential input?

If the console has a real differential input, you might need:

1. Pin 2 and pin 3 straight, pin 1 lifted.

2. Pin 2 and pin 3 straight, pin 1 tied to pin 2

3. Pin 2 and pin 3 straight, pin 1 tied to pin 3

4. A transformer

Depending on how the output of the SPX90 is configured.

If the console does not have a real differential input, the transformer is
probably the only real solution.

Get things working right without any input connected.... THEN connect up the
input and see if you get a different set of problems there.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Gareth Magennis wrote:

I have the schematics and both input and outputs are unbalanced.

That explains the problem, yes.

Sounds like it's transformer time, especially if the console is really
not differential either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Funnily enough I repaired yet another SPX90 today with the same power supply
problem I outlined earlier.

For those interested, the Caps that go are C23 and/or C24, 1000uF/10v and
2200uF/10v both radial, though you probably wont find 10v versions easily so
use 16 volt instead.

Yes, that does explain plenty.

Thanks for your help guys.

Rob

"Scott Dorsey" wrote in message
...
Gareth Magennis wrote:

I have the schematics and both input and outputs are unbalanced.

That explains the problem, yes.

Sounds like it's transformer time, especially if the console is really
not differential either.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."