PSN-L Email List Message
Subject: Re: Seismograph noise problem
From: ChrisAtUpw@.......
Date: Mon, 11 Feb 2008 18:53:34 EST
In a message dated 11/02/2008, lconklin@............ writes:
Regarding corrosion under solder joints, I haven't really checked
thoroughly for that yet, but the board looks very clean.
Hi Larry,
I had a whole Sony TV with crevice corrosion. The joints looked perfect,
but you could peel them off a black corrosion coat on the circuit strips. I
had to unsolder, clean and resolder every joint on the **** board.
Re. your and Roger's comments about the cover, It will take me a little
time to build a new one.
Putting the cover on the floor isolates the seismometer from pneumatic
effects. I use 2" Celotex, but it isn't cheap. Bubble wrap can also be very
useful in reducing temperature changes and drafts ....
One other thing that I'd be interested in hearing your thoughts on is
the fact that the "noise" isn't really as random as I'd expect from
something like bad solder joints and such. If you look at the data I
posted, especially from the LF channel, there definitely seems to be a
dominant component with a period of around 20 seconds or so.
I had noted that. It looked as if you were experiencing greatly
increased gain, rather than just random noise. This could be resistors, solder
joints, diodes or the opamp.
Do measure the DC levels on TP. Does the Red/Green LED ever light up?
The NE5534 does take about 0.5 micro A to drive it - quite thirsty...
Try tapping the components?
Unsoldering C49 would isolate everything downstream of the first two
opamps.
Could there be any strong radio signals at 2 / 4 / 8 / 12 MHz? You do
have two radio receivers on the input... Electricity Utility time switches work
off radio signals on the power lines.
Try connecting an audio amplifier to the circuit before the integrator
and listening with headphones? I have solved some noise problems this way. I
was getting quite large random pulses which seemed to be real, not
instrumental. When I listened, I heard a heavy lorry approaching a sunken drain grating
on the corner of the local main road....
I've got too many irons in the fire right now to devote full time to
debugging this, but I plan to revisit all of your suggestions. Aside with messing
with the cover a little, the other very easy test will be
to disconnect the oscillator to see what happens. I still have an old test
data file from the last time I tried it, and it doesn't look much different
from what I saw then with everything hooked up, or now.
I would expect there to be a simple fault which is sensitive to humidity
- since heating the board reduced the signal. Good Luck!
Regards,
Chris Chapman
In a message dated 11/02/2008, lconklin@............ writes:
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
size=3D2>Regarding corrosion under solder joints, I haven't really checked=
=20
thoroughly for that yet, but the board looks very clean.
Hi Larry,
I had a whole Sony TV with crevice=20
corrosion. The joints looked perfect, but you could peel them off a bla=
ck=20
corrosion coat on the circuit strips. I had to unsolder, clean and reso=
lder=20
every joint on the **** board.
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>Re. your=20
and Roger's comments about the cover, It will take me a little
time to=
=20
build a new one.
Putting the cover on the floor isolates the=20
seismometer from pneumatic effects. I use 2" Celotex, but it isn't cheap. Bu=
bble=20
wrap can also be very useful in reducing temperature changes and=20
drafts ....
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>One=20
other thing that I'd be interested in hearing your thoughts on is
the=20=
fact=20
that the "noise" isn't really as random as I'd expect from
something l=
ike=20
bad solder joints and such. If you look at the data I
posted,=20
especially from the LF channel, there definitely seems to be a
dominan=
t=20
component with a period of around 20 seconds or so.
I had noted that. It looked as if you were=20
experiencing greatly increased gain, rather than just random noise. This cou=
ld=20
be resistors, solder joints, diodes or the opamp.
Do measure the DC levels on TP. Does the Red/Gr=
een=20
LED ever light up?
The NE5534 does take about 0.5 micro A to drive=
it=20
- quite thirsty...
Try tapping the components?
Unsoldering C49 would isolate everything downst=
ream=20
of the first two opamps.
Could there be any strong radio signals at 2 /=20=
4 /=20
8 / 12 MHz? You do have two radio receivers on the input... Electricity Util=
ity=20
time switches work off radio signals on the power lines.
Try connecting an audio amplifier to the circui=
t=20
before the integrator and listening with headphones? I have solved some nois=
e=20
problems this way. I was getting quite large random pulses which seemed to b=
e=20
real, not instrumental. When I listened, I heard a heavy lorry approaching a=
=20
sunken drain grating on the corner of the local main road....
<=
FONT=20
style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I've got=20
too many irons in the fire right now to devote full time to debugging this=
,=20
but I plan to revisit all of your suggestions. Aside with messing wi=
th=20
the cover a little, the other very easy test will be
to disconnect the=
=20
oscillator to see what happens. I still have an old test data file f=
rom=20
the last time I tried it, and it doesn't look much different from what I s=
aw=20
then with everything hooked up, or now.
I would expect there to be a simple fault which=
is=20
sensitive to humidity - since heating the board reduced the signal. Good=20
Luck!
Regards,
Chris Chapman
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