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Cap or resistor? (everybody's favorite game)

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Anonymous
October 20, 2004 3:33:03 AM

Archived from groups: rec.audio.pro (More info?)

So my Allen & Heath GS3 would seem to be having this problem... Group
5 and maybe 4 (four is intermittant) is about 3 db quieter than the
other 8 busses. If I overdrive them (italian tune up) they seem to
play along for a few minutes then start dropping again. It never gets
below 3 or 4 db and I can only tell on the meter's. I can't hear a
difference. I'm thinking it's a cap or resister but maybe the meters
need to be adjusted? Anyone got advise on something like this? I could
probably handle a soldering job like this but not sure I want to find
out my skills are lacking halfway through the job. How much would a
resistor or 2 cost to have done by someone that does this for living?

cheers

garrett
Anonymous
October 20, 2004 10:12:33 AM

Archived from groups: rec.audio.pro (More info?)

> So my Allen & Heath GS3 would seem to be having this problem... Group
> 5 and maybe 4 (four is intermittant) is about 3 db quieter than the
> other 8 busses. If I overdrive them (italian tune up) they seem to
> play along for a few minutes then start dropping again. It never gets
> below 3 or 4 db and I can only tell on the meter's. I can't hear a
> difference. I'm thinking it's a cap or resister but maybe the meters
> need to be adjusted? Anyone got advise on something like this? I could
> probably handle a soldering job like this but not sure I want to find
> out my skills are lacking halfway through the job. How much would a
> resistor or 2 cost to have done by someone that does this for living?

Do you have a schematic? Try using a good channel as a reference to determine
where in the meter circuits the level drops.
Anonymous
October 20, 2004 10:56:06 AM

Archived from groups: rec.audio.pro (More info?)

>From: garrcox@yahoo.com (Garrett Cox)
>Date: 10/20/04 2:33 AM Eastern Daylight Time
>Message-id: <a727dac5.0410192233.488847ad@posting.google.com>
>
>So my Allen & Heath GS3 would seem to be having this problem... Group
>5 and maybe 4 (four is intermittant) is about 3 db quieter than the
>other 8 busses. If I overdrive them (italian tune up) they seem to
>play along for a few minutes then start dropping again. It never gets
>below 3 or 4 db and I can only tell on the meter's. I can't hear a
>difference. I'm thinking it's a cap or resister but maybe the meters
>need to be adjusted? Anyone got advise on something like this? I could
>probably handle a soldering job like this but not sure I want to find
>out my skills are lacking halfway through the job. How much would a
>resistor or 2 cost to have done by someone that does this for living?

If you have a meter for each group you can run a prerecorded test tone thru it
and see if is registering correctly.
Related resources
Anonymous
October 20, 2004 2:29:28 PM

Archived from groups: rec.audio.pro (More info?)

I would make sure it's not a connector problem first. Or it could even be
the group insert sockets. Try pushing a jack in and out of each offending
groups insert socket a few times to clean them. If that doesn't work you
could try disconnecting and connecting back all the internal connectors,
removing modules where necessary.

Forgive me if you've done all this already.


Gareth.


"Garrett Cox" <garrcox@yahoo.com> wrote in message
news:a727dac5.0410192233.488847ad@posting.google.com...
> So my Allen & Heath GS3 would seem to be having this problem... Group
> 5 and maybe 4 (four is intermittant) is about 3 db quieter than the
> other 8 busses. If I overdrive them (italian tune up) they seem to
> play along for a few minutes then start dropping again. It never gets
> below 3 or 4 db and I can only tell on the meter's. I can't hear a
> difference. I'm thinking it's a cap or resister but maybe the meters
> need to be adjusted? Anyone got advise on something like this? I could
> probably handle a soldering job like this but not sure I want to find
> out my skills are lacking halfway through the job. How much would a
> resistor or 2 cost to have done by someone that does this for living?
>
> cheers
>
> garrett
Anonymous
October 20, 2004 2:44:39 PM

Archived from groups: rec.audio.pro (More info?)

Sorry, just re-read your post properly.
If there is no audible problem, the insert sockets won't be at fault. If it
is just the metering, try putting a tone through all groups and with the
bottom of the desk removed, try wiggling and prodding and tapping connectors
and things (use a wood or plastic implement) and watch if the meters jump
about. You may be able to home in on the problem. Could be a dry joint.
October 20, 2004 2:44:40 PM

Archived from groups: rec.audio.pro (More info?)

"Gareth Magennis" <sound.service@btconnect.com> wrote in message news:<cl5fin$9kq$1@sparta.btinternet.com>...
> Sorry, just re-read your post properly.
> If there is no audible problem, the insert sockets won't be at fault. If it
> is just the metering, try putting a tone through all groups and with the
> bottom of the desk removed, try wiggling and prodding and tapping connectors
> and things (use a wood or plastic implement) and watch if the meters jump
> about. You may be able to home in on the problem. Could be a dry joint.

and if you can swap modules or cables or whatever, do that and see if
the problem follows the module or cable or whatever.


Mark
Anonymous
October 20, 2004 3:12:51 PM

Archived from groups: rec.audio.pro (More info?)

Garrett Cox <garrcox@yahoo.com> wrote:
>So my Allen & Heath GS3 would seem to be having this problem... Group
>5 and maybe 4 (four is intermittant) is about 3 db quieter than the
>other 8 busses. If I overdrive them (italian tune up) they seem to
>play along for a few minutes then start dropping again. It never gets
>below 3 or 4 db and I can only tell on the meter's. I can't hear a
>difference. I'm thinking it's a cap or resister but maybe the meters
>need to be adjusted? Anyone got advise on something like this? I could
>probably handle a soldering job like this but not sure I want to find
>out my skills are lacking halfway through the job. How much would a
>resistor or 2 cost to have done by someone that does this for living?

It's easy to replace it, the problem is finding it. The symptom you
describe could be a bad coupling cap causing a stage to be misbiased,
or it could be a bad solder joint or bad connection that has formed a
little rectifier. It could even bad a bad IC which has developed an
internal bias problem, although that's a lot less likely.

This is a problem that you find with a signal tracer, putting a signal into
the input and listening to it at each step along the signal path, tracing
along with the schematic. It could take five minutes to find, it could take
hours, depending on where it is.

Get a tech to look at it. If it's just on the meters and you can't hear
it, it could just be a problem in the metering drivers and not in the
main signal path, but again that's something that will take a signal tracer
to find. You could try putting external meters on the output and seeing if
the problem exists on the output as well as on the meters.

I'd be more worried about the intermittent group four.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
October 20, 2004 7:26:00 PM

Archived from groups: rec.audio.pro (More info?)

"Gareth Magennis" <sound.service@btconnect.com> wrote in message
news:cl5fin$9kq$1@sparta.btinternet.com...
> Sorry, just re-read your post properly.
> If there is no audible problem, the insert sockets won't be at fault. If
it
> is just the metering, try putting a tone through all groups and with the
> bottom of the desk removed, try wiggling and prodding and tapping
connectors
> and things (use a wood or plastic implement) and watch if the meters jump
> about. You may be able to home in on the problem. Could be a dry joint.

Or a couple of bad meter calibration pots. Tap these with a pencil or the
equivalent. If bad, spray with CaiLube.

Peace,
Paul
Anonymous
October 21, 2004 2:16:55 AM

Archived from groups: rec.audio.pro (More info?)

Garrett:

Before getting out your soldering gun, I'd suggest checking a couple of
things first. As described below, check the connectors for oxidation. I've
found problems in gain pots that can give rise to the sort of problem you
describe. A simple fix is to de-ox them; you can find de-ox spray at your
local electronic store.

Good luck.

--


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"Garrett Cox" <garrcox@yahoo.com> wrote in message
news:a727dac5.0410192233.488847ad@posting.google.com...
> So my Allen & Heath GS3 would seem to be having this problem... Group
> 5 and maybe 4 (four is intermittant) is about 3 db quieter than the
> other 8 busses. If I overdrive them (italian tune up) they seem to
> play along for a few minutes then start dropping again. It never gets
> below 3 or 4 db and I can only tell on the meter's. I can't hear a
> difference. I'm thinking it's a cap or resister but maybe the meters
> need to be adjusted? Anyone got advise on something like this? I could
> probably handle a soldering job like this but not sure I want to find
> out my skills are lacking halfway through the job. How much would a
> resistor or 2 cost to have done by someone that does this for living?
>
> cheers
>
> garrett
Anonymous
October 21, 2004 2:09:33 PM

Archived from groups: rec.audio.pro (More info?)

So on further inspection...

The board has a built in Oscilator at 1k and like 10k for testing the
bus. Still can't hear a difference although I wonder if the difference
is so small that I can't hear it but can only see this problem on the
meters....

later that evening...

I removed the sheetmetal off the back of the board and continue to
inspect the mass of wiring and PCB's. I notice all the resistors are
of blue colour and find that on buss 7 or 8 there are 2 that are brown
and look like something similar must have happened before I purchased
the board. Clearly this not uncharted territory. So on Bus 5 (I
believe it to be bus 5 as busses 5 and 6 are on the same PCB) I have a
couple of resistors that look, well, burnt. So I suspect it's just
that. I wonder however if they were fried wouldn't the bus just not
work all-together?

thanks for the advise.


cheers

garrett
Anonymous
October 21, 2004 5:09:22 PM

Archived from groups: rec.audio.pro (More info?)

"Garrett Cox" <garrcox@yahoo.com> wrote in message
news:a727dac5.0410192233.488847ad@posting.google.com...
> So my Allen & Heath GS3 would seem to be having this problem... Group
> 5 and maybe 4 (four is intermittant) is about 3 db quieter than the
> other 8 busses. If I overdrive them (italian tune up) they seem to
> play along for a few minutes then start dropping again. It never gets
> below 3 or 4 db and I can only tell on the meter's. I can't hear a
> difference. I'm thinking it's a cap or resister but maybe the meters
> need to be adjusted? Anyone got advise on something like this? I could
> probably handle a soldering job like this but not sure I want to find
> out my skills are lacking halfway through the job. How much would a
> resistor or 2 cost to have done by someone that does this for living?

The Resistor, Cap or dodgy joint is cheap to fix the expensive bit is
tracking down exactly which of hundreds of components or joints is Faulty as
especially with an intermittant Fault such as the one you have described
this can take some time.

Regards
Richard Freeman
Anonymous
October 22, 2004 3:08:25 AM

Archived from groups: rec.audio.pro (More info?)

A simple test would be to use a multimeter across the leads on either end of
the suspect resistors. Usually, when semiconductors (which a resistor is, by
definition, a semiconductor) burn up, they fail to conduct at all. I'd be
surprised that they'd still be working if they truly burned up. On the other
hand, some resitors, particularly power resistors, are made of brown
ceramic. Is there evidence they actually did burn up (e.g. melted/burned PC
board or solder points)?

If you think these resistors did fail, you can check the ratings on the
"blue" resistors if they have the standard color code for resistors.
Otherwise, you can measure the resistance as described above and then
purchase replacements. A simple soldering job.

Craig

--


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"Garrett Cox" <garrcox@yahoo.com> wrote in message
news:a727dac5.0410210909.3925eff9@posting.google.com...
> So on further inspection...
>
> The board has a built in Oscilator at 1k and like 10k for testing the
> bus. Still can't hear a difference although I wonder if the difference
> is so small that I can't hear it but can only see this problem on the
> meters....
>
> later that evening...
>
> I removed the sheetmetal off the back of the board and continue to
> inspect the mass of wiring and PCB's. I notice all the resistors are
> of blue colour and find that on buss 7 or 8 there are 2 that are brown
> and look like something similar must have happened before I purchased
> the board. Clearly this not uncharted territory. So on Bus 5 (I
> believe it to be bus 5 as busses 5 and 6 are on the same PCB) I have a
> couple of resistors that look, well, burnt. So I suspect it's just
> that. I wonder however if they were fried wouldn't the bus just not
> work all-together?
>
> thanks for the advise.
>
>
> cheers
>
> garrett
Anonymous
October 22, 2004 8:49:24 AM

Archived from groups: rec.audio.pro (More info?)

> A simple test would be to use a multimeter across the leads on either
> end of the suspect resistors. Usually, when semiconductors (which a
> resistor is, by definition, a semiconductor) burn up, they fail to conduct
> at all. I'd be surprised that they'd still be working if they truly burned up.

Several points, technical and practical.

Ordinary resistors are not semiconductors. The term "semiconductor" was coined
to describe materials such as silicon, germanium, cadmium sulfide, gallium
arsenide, etc, whose conductivity fell between true conductors (silver, gold,
aluminum, etc) and insulators. Semiconductors also have significantly different
properties from conductors -- for example, they usually have a negative
temperature coefficient of resistance, rather than positive (that is, their
resistance drops with rising temperature), and they often show significant
sensitivity to light.

An ordinary resistor can be damaged to where it shows large increase in
resistance without actually opening up.

Finally... If any circuit component has burned -- especially a "sacrificial"
device, such as a resistor used as a fuse -- you should try to find out why it
failed before replacing it.
Anonymous
October 22, 2004 1:34:24 PM

Archived from groups: rec.audio.pro (More info?)

Often you will find that desk manufacturers fit "fuse" resistors on the
power supply inputs to each module. These are a different type and colour
to normal ones. Someone may have replaced these at some point on buss 7 and
8, or perhaps they are burnt normal resistors, possibly only partially burnt
due to an accidental short circuit one time, causing by poking and prodding
with a metal inplement instead of a wood or plastic one :)  Measure them in
circuit and see if there is any difference with a good channel.

Gareth.

(AFAIK, fuse resistors are flameproof and will fuse at a lower current than
a normal one)


"Garrett Cox" <garrcox@yahoo.com> wrote in message
news:a727dac5.0410210909.3925eff9@posting.google.com...
> So on further inspection...
>
> The board has a built in Oscilator at 1k and like 10k for testing the
> bus. Still can't hear a difference although I wonder if the difference
> is so small that I can't hear it but can only see this problem on the
> meters....
>
> later that evening...
>
> I removed the sheetmetal off the back of the board and continue to
> inspect the mass of wiring and PCB's. I notice all the resistors are
> of blue colour and find that on buss 7 or 8 there are 2 that are brown
> and look like something similar must have happened before I purchased
> the board. Clearly this not uncharted territory. So on Bus 5 (I
> believe it to be bus 5 as busses 5 and 6 are on the same PCB) I have a
> couple of resistors that look, well, burnt. So I suspect it's just
> that. I wonder however if they were fried wouldn't the bus just not
> work all-together?
>
> thanks for the advise.
>
>
> cheers
>
> garrett
Anonymous
October 23, 2004 1:06:27 AM

Archived from groups: rec.audio.pro (More info?)

I did some testing and this is exactly the result I get. I am
wondering if it was the "sacrificial" resistor that failed. I have the
schematics but I'm pretty poor at reading them. I guess I'll just have
to replace it and watch it for a few weeks to see if the problem
reoccurs. Thanks to you all for your insight and experience.


cheers


garrett


>
> An ordinary resistor can be damaged to where it shows large increase in
> resistance without actually opening up.
>
Anonymous
October 23, 2004 5:48:56 AM

Archived from groups: rec.audio.pro (More info?)

On Thu, 21 Oct 2004 23:08:25 -0700, "ceedub"
<craigmw@EFOFFSPAMcox.net> wrote:

>. Usually, when semiconductors (which a resistor is, by
>definition, a semiconductor)

It semi-conducts, in so much as it resists. But, by that definition,
every circuit component except a super-conducting wire would be a
semiconductor. As you well know, the term has a different usage.

CubaseFAQ www.laurencepayne.co.uk/CubaseFAQ.htm
"Possibly the world's least impressive web site": George Perfect
Anonymous
October 23, 2004 3:03:24 PM

Archived from groups: rec.audio.pro (More info?)

On 22 Oct 2004 21:06:27 -0700, garrcox@yahoo.com (Garrett Cox) wrote:

>I did some testing and this is exactly the result I get. I am
>wondering if it was the "sacrificial" resistor that failed. I have the
>schematics but I'm pretty poor at reading them. I guess I'll just have
>to replace it and watch it for a few weeks to see if the problem
>reoccurs. Thanks to you all for your insight and experience.

Resistors don't generally fail spontaneously. They fail because an
inappropriate current flows through them. Something caused this to
happen.

If you'd been lucky, someone experienced with these units would have
said - "Yeah. This is a common fault. Replace components X, Y, Z."

You weren't lucky. Take it to a repair shop. The bill will be less
if he doesn't have to clear up after your botched attempt first.

CubaseFAQ www.laurencepayne.co.uk/CubaseFAQ.htm
"Possibly the world's least impressive web site": George Perfect
Anonymous
October 25, 2004 2:05:43 AM

Archived from groups: rec.audio.pro (More info?)

In article <a727dac5.0410210909.3925eff9@posting.google.com>,
garrcox@yahoo.com (Garrett Cox) wrote:
> I removed the sheetmetal off the back of the board and continue to
> inspect the mass of wiring and PCB's. I notice all the resistors are
> of blue colour and find that on buss 7 or 8 there are 2 that are brown
> and look like something similar must have happened before I purchased
> the board. Clearly this not uncharted territory. So on Bus 5 (I
> believe it to be bus 5 as busses 5 and 6 are on the same PCB) I have a
> couple of resistors that look, well, burnt. So I suspect it's just
> that. I wonder however if they were fried wouldn't the bus just not
> work all-together?

Some resistors, like the excellent Dale metal films, have a nice milk
chocolate brown color when they're brand new. Many commercial metal
films from KOA and others in Japan have a light blue color. None of
them have been cooked, and it's hard to make a blue one turn brown
without also burning the PC board severely. Your board may have been
stuffed with a mixture of two vendors parts. Not a problem, and not
necessarily a sign of rework or damage.

I don't know what the actual issue is here since I jumped in late, but
brown resistors aren't automatically a sign of burnt resistors. Those
brown Dale parts are actually quite nice ones.


Best of luck with whatever the problem might be,

Monte McGuire
monte.mcguire@verizon.net
!