Need help fixing thermal imager.
I have an Argus EEV P4438 Thermal Imager.
Here's the link to the pdf.
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