Hi Larry,

Have you tried locking down the pendulum so it can't move and letting you system run 
for a while? Looking at the schematic I see two parts I would replace. They are the 
two back-to-back 100uf (I think) capacitors driving the feedback coil. I would 
replace them with one 47uf non-polarized cap. DigiKey has these 
http://www.digikey.com/product-detail/en/ECE-A1VN470U/P1190-ND/227631 in-stock.

Regards,
Larry Cochrane
Webtronics

On 6/20/2012 7:11 PM, Larry Conklin wrote:
> Hi Roger,
>
> I think I remember your having posted an account of your "rug affair".
> In fact I think that it prompted me to improve the leveling screws on my
> system, which at the time were rather flimsy. I replaced them with
> larger, stiffer screws and I think that it may have helped, or even
> "solved" the problem for a while.  I'm now using fairly substantial
> screws and the system is (and already had been) sitting on a couple of
> 1/8 inch thick strips of aluminum that are epoxied to the basement
> floor.  The assumption being that the plates are a more rigid surface
> than the bare concrete would be.
>
> The only pivot points I can identify are the pendulum hinge itself
> (consisting of thin metal shim material, phosphor bronze or some such).
> But there is certainly the possibility that the contacts between the
> feet and the plates might shuck around a little with temperature changes?
>
> I also have had a series of cover experiments.  Original cover was a
> wood box that sat on the frame of the sensor.  Very bad idea. Rebuilt it
> to fit over the sensor and sit on the floor.  Better, but probably
> vulnerable to transmitting noise to the instrument.  Added "stuffing" to
> fill up the unused volume and suppress air movement. Not much noticeable
> change.  Current cover is light weight, built of insulating board and
> sitting on the floor.  At times I've duct taped it to the floor, but at
> the moment it's just sitting there.  Maybe putting the tape back would
> be a good idea.
>
> But the overall behavior of the problem makes a lot of these
> possibilities seem unlikely.  In one subset of episodes of the problem,
> the noise starts abruptly and then continues indefinitely for days of
> weeks at a time.  The data shown on my web page is typical of this
> "class".  (And I noticed that this episode started on March 30, and is
> still ongoing, although there were couple of periods of a week or so
> duration since them where things were much better.)  Other episodes have
> emerged gradually over the course of several hours, continued for days
> or even weeks at a time and then subsided.  I'm at a loss to come up
> with a theory that is consistent with both kinds of behavior.  And none
> of the experiments I've tried have made any clear and lasting impact on
> the problem, although I've tried a few things that I've thought fixed
> it, only to have it crop up six months later.
>
> I guess that's what makes this business interesting.
>
> Larry
>
>
>
> On 6/20/2012 9:41 AM, RSparks wrote:
>> Hi Larry,
>>
>> My experience parallels yours with loose mounted components.  I once
>> went through a rug to concrete below and failed to make good contact
>> with one screw on the concrete.  I was effectively floating on the rug
>> with one of the three seismometer legs!   Very noisy!
>>
>> Based on this experience, I am careful to make all mechanical contacts
>> solid connections in some way.  I even drilled holes into the concrete
>> and mounted my seismometer solidly.  I thought there was a small
>> improvement in the noise level after taking this somewhat extreme
>> measure.
>>
>> I also avoid pivot points in favor of bending joints to avoid noise.
>> Friction is present in our seismometers if there is a moving joint and
>> mechanical friction is always noise.
>>
>> Maybe look more carefully at any mechanical connection that might be
>> loose, maybe  not only in the leveling screws.  Look also at the
>> mounting of the surrounding air/insulating box, making sure it is not
>> rocking from the ever present 0.2 Hz peak noise or more likely, the
>> thermal air currents in your room.
>>
>> Good luck,
>>
>> Roger
>> .------ ------ ------ ------ ------ ------ ------ ------ ------
>> ------. | Message 3 | '------ ------ ------ ------ ------ ------
>> ------ ------ ------ ------' Subject: Haunted system misbehaving again
>> From: Larry Conklin  Date: Tue, 19 Jun 2012
>> 14:54:30 -0400 I have an SG sensor that has intermittently had serious
>> noise problems, literally for years. Mechanically, it is very similar
>> to the design that is shown on Larry's PSN web site, and it uses
>> Larry's electronics board, which I believe he is no longer selling.
>> When the thing is running properly I've been quite happy with it. But
>> occasionally, for reasons I have never been able to pin down, it
>> exhibits extreme low frequency noise, to the point where it is
>> basically useless. The current episode began with the system running
>> very well, but it was in need of leveling, which I've typically need
>> to do every couple of weeks or so. Before I adjusted the leveling
>> screw, it was quiet. After messing with it it became extremely noisy.
>> So, you'd believe that it was some sort of mechanical problem, right?
>> And I've had several other episodes that began the same way. This
>> time, when I brought it upstairs on the bench, I did in fact discover
>> that the lock nut on the leveling screw was loose, and I "fixed" the
>> problem by re-tightening it. Ran pretty well for a week or so
>> thereafter, but not really as quiet as it should be. Then, it
>> spontaneously got quite noisy again, interspersed with periods where
>> it ran ok. I have a lot of other history with seemingly mutually
>> exclusive symptoms/probable causes, but the bottom line is I don't
>> have a clue what is really going on. I'm tempted to believe that there
>> is something subtle wrong with the electronics board, but in past
>> attempts to trouble shoot it, haven't been able to find anything. If
>> there is anyone out there who has one of Larry's SG boards that
>> they're willing to part with, I'd be interested in buying it. If for
>> no other reason than to rule out the board as the source of the
>> problem. For the curious, I have a little web page that I dump drum
>> reports up to daily. The report for today (so far) shows a
>> particularly noisy day, but does include the quake that happened in
>> the Aleutians this afternoon. The page also shows drum reports from
>> the day this round of the problem started. The day started just fine,
>> until the big transient that resulted when I went down and adjusted
>> the leveling, at which point all hell broke loose. You can also see
>> the consequences of two subsequent leveling adjustments later in the
>> day. After that data was recorded, I didn't mess with the thing for
>> maybe a week, until I finally got around to taking a closer look at
>> it, at which point I realized that the leveling screw was loose and
>> re-tightened it. I'd be very interested in anyone's thoughts on this
>> problem. The link to my web page follows:
>> http://home.roadrunner.com/~lwconklin/ Larry Conklin Liverpool, NY .-
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>
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