Need help fixing thermal imager.

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Need help fixing thermal imager.

I have an Argus EEV P4438 Thermal Imager.

Here's the link to the pdf.

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved0C%CkQFjAA&url=http%3A%2F%2Fwww.isbgroup.com%2Febay%2Fargus.pdf&ei=T9cQT5PhGOHRiALamqSQBg&usgAF%QjCNF40_N9ZFJJTSQZIqiL2uYrPy4HAA

It's designed for firefighters to see bodies in dense smoke.   Built in 1998
It has no absolute temperature readout.  The auto-iris adjusts the gain
and I get to see relative
temperatures.  That's fine.

When I turn it on, I get an image, but the contrast is low and the image
is negative.
Hot spots are supposed to be bright.  On mine, hot spots are dark.

If I stand barefoot on the carpet and step off, I can barely see the
image of my footprints.
A wall-wart plugged into the wall shows up prominently, but it's black,
not bright.
So, the unit is not dead, it's just not right.

After a minute or so, a white area appears on the edge of the picture
and slowly moves
toward the center.  It's like someone poured cream on the edge and it
flows toward the center.
Then the whole screen goes white.  Cycling power brings it back.

There are also some artifacts in the center of the screen.  Look kinda
like black lightning
flashes.  It's position dependent.  Point the unit down and they all but
disappear.
Point it up and they are the most prominent.  They are less prominent as
it warms up.

I've done a lot of googling and reading of patents.

The thing claims to have a TGS sensor.  The sensor looks like a vidicon
with a wire coming out the front
to a shielded box that I assume is the high sensitivity input.  Has WAY
more circuitry than you'd expect
and dozens of variable resistors.


There's a 6V NiCd battery that measures 3V and won't accept any current
at 6V.
I assume this stores some calibration stuff.  I'm afraid to replace the
battery for fear of losing
info I can't get back.  Or maybe it doesn't work because the info is
already lost???

I've found mention of  a "white out" phenomena that causes the screen to
go white when you look at very hot objects.
I'm looking at room temperature stuff only.

If I can fix the negative image issue, and the white out issue,
I might be well on the way to making it useful.


It's not worth spending a lot of money, but I'd like to make it work
properly if I can.

Anybody got any ideas on how to proceed?
Any chance of finding a service manual or calibration procedure?


Thanks, mike

Re: Need help fixing thermal imager.
Hi Mike,

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Have you tried talking to your local fire department?

First thought:  are you operating it so far out of its normal
operating range that the rules don't apply?  I.e., does the
manual claim that using it the way you are *will* produce useful
results?

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I the image presented on the video out identical?

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So, you know for a "fact" that this isn't as it should be
(you know it to be a 6V battery by counting the cells?
Can you measure individual cells to verify one or
more are toast?)

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So, you can safely ^^^^^^^^^^^^ shunt it with a *good* 6V
battery?

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Lots of pots *and* calibration constants?

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Re: Need help fixing thermal imager.
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I went to the local fire department.  The imager is older than
the oldest guy there.  Nobody had a clue.  They send newer units back
to the factory for repair, so nobody knows what's inside.

Need to stumble upon a service manual.

Re: Need help fixing thermal imager.
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OR a bad bias, bad deflection...., on the vidicon itself...

If I were you I would check around the vidicon (anodes, grids,
cathode...),  you may find the answer there

The problem is that you will most likely find no spec. for the
pyroelectric vidicon, so you have to guess for anodes, grids, cathode,
etc... and their operate voltage respectively...

That's fun enough if you have time, and beware for high voltages
around the tube




Re: Need help fixing thermal imager.
On a sunny day (Tue, 17 Jan 2012 14:35:42 -0800 (PST)) it happened halong

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Vidicon? Looks like not enough beam current.
Could be worn out heater (cathode).
Increasing the heater voltage a bit might help,
but is considered bad practice, and shortens life of the vidicon.
Playing with the grid bias may be better, maybe there is a trimmer there.
The beam current has to be just enough to compensate for the charge
released from the target by the incoming light.


Re: Need help fixing thermal imager.
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Yup, in the old days I used something like this for the tubes..

http://videokarma.org/showthread.php?p3D%3024290

Re: Need help fixing thermal imager.
On a sunny day (Wed, 18 Jan 2012 07:31:38 -0800 (PST)) it happened halong

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Yes, I have used those to repair BW tubes, and also color tubes.
Yo ucan make yoru own by using a 10W bukb i nseries wit ha diode and capacitor
rectifier.
                                            button  
                                             ||
                                            ====
  -------------|>|--------------- 10W 240V bulb --  -- CRT whenelt (grid 1)
240 V |                    |
 AC   )|| ---CRT heater   ===
      )||(12 V AC         --- 100 uF
      |   ---CRT heater    |
 ---------------------------------------------- CRT cathode
  

Connect it, let the heater warm up,
press the button until the big bulb glows constantly.
made a lot of mony 'rejuvinating' old sets with that,

Also works for color sets, you need to do it three times.

I woul NOT try it like that on a vidicon, at least never have,
but who knows if all else fails.
Vidicon current is normally just a few uA.

BW sets go to several hundred uA, color sets to 1.5 mA per gun.

Re: Need help fixing thermal imager.
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Just the idea of rejuvenating for old tubes (if it's the case)

Agree to make sure to limit the current for the vidicon.  He can't use
one like that anyway until re-arrange the socket...until then he must
know well about the vidicon's spec


Re: Need help fixing thermal imager.
On a sunny day (Wed, 18 Jan 2012 12:54:34 -0800 (PST)) it happened halong

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Right, some vidicon I used had for exampe a 6 V heater.

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