Author Topic: (new pic posted, please help) Cairns Viper, self-heating, some other questions  (Read 5664 times)

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Offline Bill W

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Voltages with and without the peltier connected.  Resistance likely less interesting.

The idea is to work back until we find where the output of a bit of circuit is no longer reasonable when compared to the input.
The important thought is that 'garbage out' is OK if it is correct for a given 'garbage in'.

The circuit operating principles will be along the lines of any Peltier drive IC even if built from discretes, maybe a micro, and (op-amp+TR) instead of the mosfets.

Maybe see how much of this is in there:
http://www.anderswallin.net/2013/08/tec-drive-prototype/
http://www.anderswallin.net/wp-content/uploads/2013/08/sbea001_tec-drive_v3.png

There will be a comparator (or high gain op-amp) to compare the reference to the sensor temperature feedback
There will be an integrator
You already have the output drive stage (opamp and 4 transistor)


Bill


Offline Logan

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Here's the raw test result for the OP295 on the back of the sensor board:

No TEC, just on
45
154
978
7
10
167
749
350

No TEC, 15min
56
154
972
6
9
166
740
349

TEC on, 3min
4520
2191
2185
6
1451
1448
1775
6140

TEC on, 25min (high temperature warning on)
5890
1513
2189
13
44
985
175
6115


Tested voltage against GND, all numbers are in mV, DC mode. Sequence are pin number defined in official spec sheet:
https://www.analog.com/media/en/technical-documentation/data-sheets/OP295_495.pdf
« Last Edit: October 07, 2021, 04:35:28 pm by Logan »
 

Offline Bill W

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Ok I'd conclude that:

The 'TEC connected' is in fact power to the device and driver.
(as pin 8 is not 6100 or so unless TEC connected)

Initially the device is working OK (for itself) if not what you would want it to be doing
(pins 2/3 and 5/6 very close, 1 and 7 not at limits)

Does run flat out eventually
(pins 2/3 and 5/6 no longer close, 1 and 7 hit rail)

Now need to find where pins 2, 3, 5 and 6 come from.

Bill
 
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Offline Logan

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Thank you Bill and sorry for the late reply.
Where should I find them? There are too many components...
 

Offline Bill W

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No idea, you are going to have to look and probe. 
First check if they go to any of the connectors on the PCB (ie come from another PCB) or look to track back the traces.

I'd expect the inverting input on each op-amp to attach to the (joined) emitters of each pair of  the drive transistors very like the attached opamp drive booster.

The non-inverting ones are the interesting one to follow.

Bill
 
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Offline Logan

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Now need to find where pins 2, 3, 5 and 6 come from.
Thank you for help.
Please look at the picture and tell me what to do next.
 

Online Fraser

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Logan,

As no one has responded yet, I will comment.

Well done for tracing the interconnections in the H Bridge that drives the Peltier Element  :-+

Now the bad news. Diagnosing a fault and tasking another person to do diagnostic tests remotely is very challenging and time consuming. I have had a lot of experience of doing this and sadly stopped taking on such tasks some time ago as a diagnostic that would take me less than 15 minutes with the patient on the bench was taking hours of my time via messages to someone else doing the work. This is likely why you had limited responses to your request for help with this camera. Without schematic diagrams, working on thermal imaging cameras can be very challenging. I address that issue with complex faults by reverse engineering the area of the camera that I believe contains the fault. This is a time consuming task but is sometimes justified in time saved by not stumbling around a PCB in the dark looking for faulty components.

You have begun the process of reverse engineering the Peltier element control circuit but, alas, there is more work to do. Once the interconnections of the various components have been established, a proper schematic diagram needs to be drawn to provide a simple and clear picture of the circuits operation. The Peltier driver H Bridge is the output drive section of the Peltier Element controller. There will be control signals or voltage levels coming from other components on the PCB and it is important to reverse engineer that area of the design as well as that may well be where the issue with your camera resides.

Repairing thermal cameras is not a simple task for anyone not experienced in electronics repair and PCB reverse engineering. It can take a long time to build up the knowledge required to do it efficiently. It is certainly not a technology on which to ‘cut your teeth’ as no schematics are available. By comparison, repairing a laptop PC is relatively simple as schematic diagrams have often found their way into the public domain.

I am sorry that I cannot move forward with you on this repair adventure but I just do not have the spare time at the moment.

Fraser
« Last Edit: October 30, 2021, 12:04:21 pm by Fraser »
 
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