Thermal Camera Teardown - The FLIR TAU 320 by Fraser

[Fraser]

I recently purchase a faulty FLIR HS324 thermal camera/scope in the hope of restoring it to full operation. I traced the failure to the TAU core which is a bit of a nightmare on the repair front. The Tau core in the HS324 is a TAU320  that produces a 320 x 240 image. This particular implementation use a standard TAU with some additional modules attached to its rear. I will not be covering those modules in this post as they are being included in my HS324 thread.

The good news is that a failure in the TAU means that you will get to see inside this camera core. In order to investigate the fault I have used another TAU 320 as a working reference core from which I can the readings. This thread will include pictures of PCB's from both cameras and a comparison of them as they are differing revisions.

Pictures follow. I am providing the normal VGA resolution images plus some slightly higher resolution images of the more intricate parts. There will be plenty of pictures for those interested in the TAU and I will also be commenting on my fault finding progress.

On with the show.....

Fraser

[Fraser]

The interior views begin.......

[Fraser]

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[Fraser]

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[Fraser]

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[Fraser]

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[Fraser]

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Good PCB on Left, Faulty PCB on right

[Fraser]

The Microbolometer.

Note that it is a high quality encapsulation and superior to that found in such cameras as the Ex series.

Fraser

[Fraser]

More......

[Fraser]

Fault tracing ......

I hot wired the TAU interface PCB that is used in a FLIR PS32 in order to power the TAU cores for testing. The TAU needs no other support in order to produce an image. The indication of normal operation is the twin FFC event just after power is applied. Failure to produce these two events indicates a critical error or fault in the core. My faulty core does not produce that twin FFC event and no video is output.

Access to the PCB test points in the TAU is made more difficult by the close proximity of the adapter PCB that I am using. I have been using PCB track repair wire to extend the test points to a more accessible position.

The components on the TAU are small in order to keep the unit compact. 0402 discrete passives are used all over the small PCB. Good magnification is needed to work on the PCB.

Comparisons with my working TAU PCB revealed that the faulty TAU PCB has a problem with its 12V supply rail which is reading only 9.3V. The 12V rail is generated from the main 5V supply using an LM27313 Boost regulator. testing revealed that the potential divider in the Boost converter feedback path is in trouble. One of the resistors was way off value and so has been removed. I will fit a replacement resistor and its associated parallel 220pF capacitor tomorrow. This may, or may not, be the only fault on the unit. We shall see. I am getting too old to be working with 0402 components !

In the attached picture there are some bare pads in front of a larger brown 4.7uF SMT capacitor. These are where the removed components once sat.
 
Fraser

[Chanc3]

Great teardown as always - saving me from my curiosity as always! I don't think my boss would appreciate me taking out Tau apart!

Looking forward to the repair results!

[Kilrah]

Nice, beautiful construction!
And I'm wishing for more 1600px photos, the 640px postage stamps are always a bit deceiving!

[Fraser]

I will certainly include more higher resolution pictures in the future. The 1Mb file limit does constrain image resolution and I can only upload posts every 60 Seconds so two images per minute.

Fraser

[Fraser]

It should also be noted that the TAU is not a FLIR design. It is an Indigo product that came to FLIR when they purchased Indigo.

With modern integration there is not much to be seen inside the TAU camera.  A small double sided PCB is all that is needed. Impressive. The LEPTON is another impressive example of thermal camera miniaturisation. Miniaturisation of thermal cameras will always be hampered by the physical requirements of the microbolometer and it's lens though.

Fraser

[Kilrah]

Interesting, is that the reason for your 2 PCBs being different, i.e one being the original Indigo design, and the other a Flir-designed minor rev?

Instantly looks even more modern/advanced knowing that the design must then date from before 2003...

[Fraser]

Indigo were specialists in thermal camera miniaturisation. That is why FLIR bought them and their expertise.

Both my Tau cameras are from the FLIR owned era, but there are different revisions of this platform. It's predecessor was the Photon. A similar camera but a little less integrated.

Fraser

[Fraser]

I am investigating the 'faulty' 12V rail on the failed Tau PCB. I want to be sure that this revision of board is supposed to have 12V on that rail.

Time to reverse engineer that part of the PCB.To help me, I put the PCB in the high resolution X-Ray machine. As you can see, this is a reasonably high component density board with several layers. The X-Ray image gives me the information I need in the area around the 12V boost converter though. I include the X-Ray images for your interest.

Fraser

[Fraser]

Using the physical magnification available in the MX-20 I closed in on the 12V Boost Regulator area. The MX-20 also provides a zoom feature an further image enhancement but this is good enough for my needs.

Fraser

[Fraser]

For comparison, a Raytheon PCB from an EEV Argus camera that basically does the same job as the TAU pcb. There are two versions, Analogue, and Digital, so I have included both types fro interest.

Fraser

[Fraser]

A couple of PCB dimension reference images to show how compact the Tau Core PCB is. The tiny 0402 passives are barely visible to my 48 year old eyes so I use a microscope to work on this sort of kit.

Fraser

[Fraser]

For those interested in the chips used on the Tau PCB, here they are:

KLB = BAT54BRW Schottky Barrier Diode array
6210 = BD6210  DC brushed motor driver for FFC flag drive
EP3C25U256 Cyclone III  FPGA - The 'brains' of teh TAU
SRPB = LM27313  Boost converter for 12V rail
25P64 = M25P64  64Mbit serial Flash SPI
PDII = TPS3828-33   Voltage monitor & supervisor IC
BYJ = TPS62240 300mA step-down converter
BQE = TPS62400 400mA step-down converter
ADV7127 10 Bit 240MHz D to A converter
D9JRN = MT46H8M32LFB5-6   256Mb SDRAM  2Mb x 32 x 4

Fraser

[Fraser]

The 12V rail on the working TAU Core is making me scratch my head.

The chipset on the TAU PCB requires the following voltages +1V2 , +1V8, +2V5, +3V3 and +5V0

There is no obvious requirement for +12V that I can find on the PCB. Even the 'RS232' data link is 3V3 only.

The 5V supply rail is up converted to +12V and this is fed the Microbolometer PCB. On that PCB, the +12V feeds a LT1761 (marked LTGC) LDO +5V regulator. That regulator is intended to provide a well regulated low noise supply of +5V. No great mystery there, but why boost to +12V ?

If that is the only purpose of the '12V ' supply, then the +9V3 supply on the faulty unit would be more than enough to meet the needs of the LT1761.
Hmmm more investigation needed.

Fraser

[Kilrah]

On that PCB, the +12V feeds a LT1761 (marked LTGC) LDO +5V regulator.

Are you sure it doesn't also go straight to the sensor?

If not I'd check the output of that LDO, there could be a problem downstream of it that loads 5V too much, in turn loading the 12V too much... in which case the problem would not be the 12V rail itself, but whatever draws too much.

[Fraser]

@Kilrah,

Thank you for the comments.

I tested the voltage of the power supplies with the Microbolometer disconnected so thankfully the microbolometer is not loading the '12V rail'. I have yet to find any components using the '12V rail' on the PCB and can find no low impedances on that rail. It also worth mentioning that i monitored the current draw from my PSU when powering the good and faulty PCB's. Both drew 134mA. this suggests no excessive loading on any rail WRT to a known good board. There are some minor differences between the two PCB's including the FFC Flag motor driver IC running off of the 3V6 rail on the faulty PCB and the 5V rail on the good PCB. I am wondering if the 9V3 reading  found was indeed legitimate. No harm dome as I have not changed the rail to 12V yet   

I was tired when I was looking at the supply voltage lines and now I look at the Boost converter again, I doubt that the potential divider was faulty as a resistor normal cracks, going O/C or high in value. That would wildly change the output voltage, not just change it by 3V. There is always a risk when using a different revision of PCB as a voltage reference unless you are certain that the supply rails are unchanged between revisions.

Fraser
 

[Fraser]

When working on a faulty PCB without schematics, I always draw up a simple block diagram showing the interconnection of the various modules, PCB's and major components. This provides an easy topology reference and diagram on which to annotate test results.

The block diagrams are usually pretty rough and always hand drawn. I attach my present diagram for the TAU320 for others reference. Please note that this is a sketch and is not supposed to conform to any schematic or block diagram standards, it is just my shorthand when repairing kit 

As you can see, the camera PCB is actually pretty 'simple' in terms of the number of IC's used. The FPGA is the brains of the outfit and enables such integration.

The Video DAC produces the composite video signal for direct feed to the Hirose I/O connector with no buffering.


UPDATE: The Block diagram has been updated and corrected. You will find the latest version here:

https://www.eevblog.com/forum/thermal-imaging/thermal-camera-teardown-the-flir-tau-320-by-fraser/msg1004215/#msg1004215

I am removing the old version from here as it could cause confusion.

Fraser

[bktemp]

Would it be possible to use boards from the working unit to see which board is faulty?
Could it be a dead sensor? It looks like all the analogue stuff is integrated into the sensor, so if the FPGA does not receive any valid data from the sensor it may go into fault mode.
What happens if you connect the sensor from the dead unit to the good one?

MT46H8M32 is a DDR SDRAM, not an SRAM.

[Fraser]

@bktemp

Already done 

The working PCB works fine with the non-working units microbolometer PCB and sensor. Obviously the calibration and NUC data is invalid, but it works. The 'main' PCB is at fault.

Thanks for the typo correction 

Fraser

[bktemp]

Good to hear that the sensor is ok.
Debugging such a dense design is probably very difficult unless it is a rather simple analogue problem, because almost all signals are hidden on the inner layers.

Could it be corrupted NUC/calibration data?
It looks like the FPGA is running, so the main block of the SPI flash must be ok. The calibration data is probably stored at the end of the flash after the FPGA code.
If you can't find any hardware fault, you could try to copy the SPI flash from the working unit.

[Fraser]

As added information for others working on these cameras.

Even without the Microbolometer pcb connected, the TAU PCB will output a composite video image with the FLIR LOGO in the top right corner. The green FFC event square also appears in the top left corner after initial power on. This camera board does not seem to care whether or not it is receiving information from the microbolometer and, unlike my PM series cameras, there is nothing on the microbolometer PCB needed for completion of boot. 

So in summary

1. Disconnect the Microbolometer PCB ribbon from the main PCB connector
2. Connect an NTSC monitor between Pin 19 of the ADV7127 video DAC and the 0V rail
3. Apply +5V to the PCB via the Hirose connector or direct to the power input filtering chain
4. The TAU PCB will boot and draw 134mA at 5.0V
5.The FLIR Splash screen will appear
6. A plain grey screen will appear with the white FLIR Logo in the top right corner

If you do not get the same as above, your main PCB is likely not operating correctly

Fraser

[Fraser]

@bktemp,

Sadly I am not certain that the FPGA is working correctly, or even running 

I did think the TAU was generating the colour bar display whilst it was in the HS324 camera, but sadly that is incorrect. The colour bar display is in fact being generated by the later video stages that are fed with video from the TAU. I believe the video stage generates a colour bar image until a valid video signal is presented to it. As the faulty TAU is not producing any video, the colour bar display remains active.

Fraser

[Fraser]

Next steps will be to recheck all power supply rails after I fit parts to replace those I removed from the 9V supply. I will then start the usual checks on clocks, reset lines, bus activity etc. The FPGA Reset line is connected to an LED so I can see that the RESET is not asserted.

Compared to other cameras that I have worked on, this is relatively simple in some ways. Far fewer components to check. That said, it is high density and access to some IC pins will be challenging, if not impossible.

Fraser

[Kilrah]

I would think the FPGA is running if you say the current drawn by both boards is identical. An unconfigured FPGA will typically have a significantly lower consumption than one that's running.

Since no video seems to be the main fault I'd start checking the video path starting from the output...


EDIT: Forgot the shutter issue... 

[Fraser]

Kilrah,

Thank you. I completely missed that an unconfigured FPGA will draw less current. Good spot chaps and very helpful.

Yes the lack of the FFC flag activation is a fly in the ointment. Otherwise I would be looking at the video DAC for a failure.

The FPGA may be configured, but in some form of HALT due to an issue that I have yet to discover. I shall have to spend a little time on this little core and attempt RS232 communications with it.

Thanks for the input guys, very much appreciated 

Fraser

[Fraser]

Some 'quick & dirty' screen captures of the good TAU PCB running with just a 5V supply and Pin 19 of the video DAC connected to a test monitor. Note that the test monitor has a single white pixel fault that is nothing to do with the TAU. The 'AV2' annotation is generated by the test monitor so I know which input channel I am monitoring.

Fraser

[Fraser]

More of my TAU diagnostic 'working notes'. Yep they are ugly, but good enough for what I need during a repair 

This time identification of the power supplies used in the TAU 320 main PCB. Other separately regulated supplies exist on the Microbolometer PCB.

I have indicated the inductors associated with each supply rail as they are easy to identify and you just test the voltage at the inductor output.
On the boost and buck converters the layout of the circuit is very simple and clear so the schottky rectifier diodes and smoothing capacitors may also be easily identified.

The indicated supply voltage are theoretical values so I have tested my working PCB with the microbolometer disconnected and just a 5V0 supply connected to it. The 'real world' voltages for each rail are as follows:

1V2 Rail = 1V210
1V8 Rail = 1V825
2V5 Rail = 2V512
3V3 Rail = 3V348
3V6 Rail = 3V633
5V0 Rail = 5V000 (as set on Power Supply)
12V Rail = 11V59

On my faulty PCB there was a 9V0 Rail in place of the 12V0 Rail

9V0 Rail = 9V30

All voltages measured with a Fluke 87 III multimeter

PCB current consumption = 134mA Stable

Fraser

[bktemp]

It looks like most pins of the BGA packages have a via next to it. So it should be easy to look at the CLK pins of the DDR SDRAM. If the differential clock is present, the FPGA is running.
You can also check the clock line and the data lines at the video dac.
Since all voltage rails are fine, my guess would still be corrupted SPI flash data, because there is not much else on the PCB that can go wrong except from broken solder joints or vias.

[Fraser]

Hi bktemp,

Many thanks again for your help on this. I would be the first to admit that working with FPGA chips is a bit of a nightmare for me. They are great for the designer and integration, but a nightmare to diagnose faults as they do so much inside that little BGA package, with no way to know the configuration unless you are the designer. What I do like about them though, is the fact that they are configured on boot rather than a custom one time programmed device or mask programmed device. If one fails, you just put another one in and the Flash chip provides the configuration at boot Well that is my limited experience with them anyway. Far better than custom programmed chips IMHO.

If the FLASH has been corrupted, I may have a challenge on my hands as that will contain the essential Microbolometer dead pixel and NUC data.

I hope to have some time to 'play' this afternoon so may make some progress with the diagnostics. It is fortunate that I have a working unit that can provide, hopefully, useful reference data to compare with the faulty PCB.

Fraser

[Fraser]

An updated and corrected TAU 320 block diagram plus the schematic of the +5V supply input filtering.

With regard to the +5V input, it has no reverse polarity protection and FLIR warn of this in the User Manual. I would have expected a diode across the 5V rail and a very fast IC protection fuse in line with the supply input. This camera is not exactly cheap !

Fraser

[Fraser]

OK, I have 'proof of life' from the faulty TAU core 

She is currently failing to initiate the two FFC events that sort out the image and vertical lines in it. There is no input occurring to the motor FFC Flag driver IC, and no green square in the top left of the image to show the FFC event is about to start.

Pictures attached. Note the Indigo Logo on this TAU at boot. You will recall that I said it was an Indigo design and not from the FLIR designers.

More when I have some spare time.

Fraser

[Fraser]

My hand in front of the lens. All seems to be working except FFC.

[Chanc3]

My hand in front of the lens. All seems to be working except FFC.

I don't mean to sound silly or anything, but is the shutter stuck?

[Fraser]

Hi Chanc3,

No, sadly not so simple. I attached the whole optical and microbolometer assembly to the good PCB and it worked fine, including the shutter. There is also the matter of the green FFC warning square not appearing and no signal to the motor driver to actuate the flag.

I have just received some USB to 3V3 UART adapters that use the CP2102 chip. This is what lives inside the FLIR USB adapter module. I will make a DIY version of the FLIR adapter module and use the FLIR GUI to see how the TAU is configured. etc. Sadly I have virtually no spare time at the moment.

Fraser

[Fraser]

For anyone wanting to connect to a TAU core without the FLIR VPC module, here is the information you need.

The FLIR VPC  provides the following facilities to the user:

1. 5V power for camera from USB source or external 5V power supply. Current at boot is ~500mA dropping to a nominal 180mA

2. USB to Pseudo 'RS232' conversion, providing the required 3V3 levels for the core.

3. Analogue Composite video output NTSC or PAL depending upon core settings.


So what 'lives' inside the VPC ?

In truth I do not know as I have not seen one up close. I do know that it contains a CP2102 USB to UART converter that provides a 3V3 TTL output. The VPC may contain some power input protection, I would hope so for what it costs.

To build your own VPC you will need the following parts

1. Hirose DF12-50DP-0.5 header connector (costs less tha £1 from Farnell)
2. Some form of PCB on to which to attach Hirose connector. Pin pitch is 0.5mm
3. CP2102 converter PCB from ebay (costs less than £2.00)
4. Video connector of your choice
5. Micro USB cable
6. Micro USB Power supplu 5V, 1A max (optional)

The pins that must be connected to the core connector:

Pin   Function

1     RS232 TX
2     RS232 RX
5     D Gnd for RS232
43   Video out High
44   Video out Low
47   0V
49   0V
48   5V
50   5V

Note that the TAU core provides a Hi-Z analogue video output that is intended to be terminated with 150 Ohms or 75 Ohms depending upon user requirements.

I would add a protection diode across the 5V supply rail and a series high speed fuse to offer some protection to revers polarity errors.

All this costs a few pounds and is pretty easy to build. The official VPC costs around £150 in the UK and has to be ordered.

The TAU GUI software for testing and configuration is free and available from the FLIR download page.

http://www.flir.com/cores/display/?id=51880

The software comes with the CP2102 driver software and installs it after the GUI installation is complete. Power can come from the USB port so no other power supply is needed. The CP2102 PCB that I bought from ebay includes a 5V output pin for just such use.

I include pictures of the FLIR VPC, CP2102 PCB, Hirose DF12 connector information and an extract from the TAU manual detailing the interface and pin layout.

UPDATE: Note that the TAU uses inverse UART polarisation. Tht is to say, Logic 0 = +3V3 and Logic 1 = 0V. You need to place a 74HC04 inveter IC in line with the RX and TX lines if using a standard USB to CP2102 adapter. Take the 3V3 supply for the inverter from the CP2102 PCB. All will work well then.

Fraser

[Fraser]

I have all the parts I need to make a DIY VPC adapter. see pictures.

Surprisingly the prototyping PCB has the exact same mounting hole spacing as the FLIR PS32 adapter PCB. I will join teh two PCB's together with some stand-offs and 2.5mm screws.

I decided to X-Ray image the PS32 adpater PCB to see how it is configured. It is a hybrid FPC/FR4 PCB so I was looking for hidden tracks within the layers. Those images will be in my next post. It sure makes life easier when you can X-Ray image a PCB.

Fraser

[Fraser]

Both sides of the FLIR PS32 adapter PCB that connects the TAU core to the controller PCB. I am 'borrowing' it from my spares donor PS32 unit to use on the faulty TAU core for tests. The adapter will be returned to the donor once I have finished with it.

Fraser

[Fraser]

X-Ray images of the PS32 adapter PCB showing all the tracks and their connectivity.

Fraser

[Fraser]

X-Ray image of the PS32 adapter FPC but I will not be connecting to the edge contacts.

Fraser

[Fraser]

I had a few minutes this evening to knock together the little TAU test jig. It is a simple little assembly so did not take long.

I tested it with the TAU PCB and the FLIR GUI for TAU cameras. The result...... communictions with the core could not be established. The CP2102 USB-RS232 bridge is recognised and working, but the camera is not responding to the GUI initialisation sequence. Tried different baud rates, tried reversing TX and RX lines, no dice. tried the working core and that behaves the same. Why can't things be simple eh 

I will have to scope the TX and RX lines to see what is going on. I will also try direct commands via Hyperterminal to see if any response can be obtained from the core. No time or inclination to do that tonight so it will have to wait.

Such is life 

Fraser

[Fraser]

Jig with TAU core fitted.

[Fraser]

I may have found the reason for the lack of communication. A chap on another forum was having the same trouble with a TAU and FLIR told him the logic on the TAU serial port is Logic 0 = 3V3  and Logic 1 = 0V.  It is inverse to normal unbuffered UART Logic. I will have to graft a 74HC04 Hex inverter in the serial comm's lines. What a PITA 

Update: I just found the interface and software design documents for the later TAU2 camera. That camera has auto detection of logic polarity but always defaults to inverse logic in the first instance. That kind of confirms that the TAU runs inverse logic. The earlier TAU does not have auto polarity detection, hence why I am having problems. Why have FLIR done this you may wonder....... well they say the I/O on the TAU follows the RS232 protocol except in terms of voltage levels. In RS232, any voltage more negative than -3V is a Logic 1, and any voltage more positive than +3V is a Logic 0. Shifting those voltage into the single polarity domain above 0V and changing to 0/3V3 logic levels results in FLIR's inverted UART logic on their camera I/O of L1=0V and L0=+3V3.

Powering a 74HC04 from the 3V3 supply rail should sort things out as that IC works down to a Vcc of +2.0V. It will just invert the TX and RX lines polarity.

Fraser

[Kilrah]

If you've got an FTDI-based USB adapter you can invert polarity in software.

[Fraser]

@Kilrah,

Thanks for the suggestion but it was just as easy to fit a 74HC04 in the end and I like the little CP2102 PCB that provides 5V and 3V3.

Fraser

[Fraser]

I installed a 74HC04 hex inverter in my Tau test jig to invert the UART TX and RX lines. Hooked it up to the laptop, ran the FLIR Tau GUI software and ...... my laptop immediately connected to the TAU. Success 

Scrolling through the Tau GUI menus provided a full run down of the cameras configuration. The FFC shutter was set to external which puzzles me a bit. The Tau normally controls its own FFC needs but being installed with the optional modules that attach to its rear in the HS-324 could mean that the micro in those add on modules controls FFC events.

I carried out a camera Reset and manual FFC and was rewarded with a nice clean grey screen as you should get when no microbolometer is fitted. I will refit the microbolometer later but expect the camera to work fine now.

I attach pictures of the modified test jig and screen grabs of the GUI pages for informational to other Tau owners.

Fraser


 

[Fraser]

GUI screen grabs

[Fraser]

More pictures

[Fraser]

More pictures

[Fraser]

More pictures

[Fraser]

After activating the test chart that is within the Tau.

[Fraser]

The correct blank grey screen after a camera reset and manual FFC

[Fraser]

Tau microbolometer reunited with the main PCB.

Tested and all working well.

The FLIR Tau GUI controls the camera without difficulty and all modes and options were tested. no faults found. the little Tau is working perfectly 
The GUI provides acess to all manner of modes that are not used in the HS324 and it is good to see that all except 'snapshot' mode are enabled and functional. X2 and X4 zoom works and even provides an electronic pan tilt mode when in Zoom mode.

Very happy about this. BUT, and it is a BIG but, is the add on module that normally commands the Tau working correctly ? There is a known issue with the early Tau module crashing. I need to get it running as a complete system and upload the later fixed firmware version to the controller module. FLIR released this as a fix for the H series cameras and it requires the add on controller and the SD card to install it. FLIR have not made Tau firmware available for direct upload via the cameras RS232 port.

At this point in time, the working Tau camera alone is worth to me what I paid for the HS324 

I just hope i can get the whole system up and running. A job for tomorrow me thinks.

Fraser

[Fraser]

Test jig and re-assembled Tau320 ready for assembly and testing

[Fraser]

Pictures from the testing phase

[Fraser]

More pictures

[Fraser]

X2 and X4 Zoom modes that include interpolation algorithms.

[Fraser]

Radiometric mode enabled.

Spot Temp and Temp range screen annotation switched on

[Fraser]

OK some comment on the TAU core crash that is detailed in this thread.

The core had crashed and locked up for reasons unknown. It would not activate its FFC shutter at boot and it was not producing a video image. It was effectively in a HALT condition.

Through fault exploration of the TAU circuit I was able to be confident that all supply rails and chips on the PCB were in a state where they should be working. This just left a firmware corruption or other similar software related cause for the cameras failure to produce an image. The firmware is not easily accessible on the TAU but if the firmware is intact and just a camera reset is needed, there is hope. I got some help with resetting the camera to a point that it would talk over its RS232 port. Once I was able to talk to the camera via its GUI, I was able to see that the FFC shutter was set to"External". That is to say, a external controller was telling the TAU when to generate an FFC event. Remember that this HS324 can record video so I an guessing that the external ARM processor that drives the TAU controls the FFC event so that it can stop the FFC whilst in video recording mode.

Why did the camera crash ? At first I blamed a known problem with early firmware but having re-assembled the HS324 to the point that i could test the complete system, I now believe there is another issue at work here.

I have set the TAU to internal auto FFC as a way of monitoring its boot sequence, and making it independent of the rest of the HS324. The HS324 was switched on and the normal boot screen of a colour bar chart appeared. The TAU booted and carried out the normal two FFC cycles as it should when set to AUTO FFC. All was looking promising. The HS324 has three power modes, OFF, Standby and ON. From Standby to ON takes but a second or two for an image to appear. From OFF to ON takes 90 seconds. I waited the 90 seconds and heard some odd behaviour from the TAU. It was making a varying whine and the FFC shutter sequence was repeating. I striped the chassis off of the TAU and the PCB's that attach to its rear so that voltage checks could be carried out. I could immediately see that the TAU was in a ON/RESET loop as the 3V3 rail monitor RESET LED and FPGA boot LED were blinking alternately. No wonder the TAU had crashed if it was in a ON/RESET loop for very long. Such is a recipe for disaster.

With the TAU power input rail now accessible I could see that the 5V rail was all over the place with very poor stability and dropping as low as 3V. The poor 3V3 power rail monitor IC had no choice but to reset the camera every time the supply dipped below the 3V3 buck converters minimum operating voltage. It is the buck converters that are producing the noise as they try to maintain their power rails. The sound is barely perceptible unless you place your ear right next to the PCB.

It is now pretty obvious that the poor TAU was a victim of a highly unstable 5V supply rail. I suspect that same unstable supply rail is causing similar issues for the ARM chip that controls the TAU. Hence no boot completion. Its supply monitor will also be having a minor fit if the supply keeps dropping. I shall investigate the cause of this irregular supply rail but at least I have something to chase down and a possible, ney likely, cause of the TAU crash.

Sadly I did not previously monitor the supply rails on the HS324 and the add on modules that attach to the rear of the TAU as my priority was to get the TAU functioning again. Knowing that the supply rail to the TAU was compromised would have helped explain the crash and I would not have searched so hard for a hardware fault in it that was not present. You live and learn eh    I did learn a lot about the TAU hardware in the process though and I enjoyed exploring it so no worries really. The camera did need to be recovered from its crashed state anyway.

The next steps will be to check the power main power supply rail into the cameras 'Power & Video PCB' and trace its through the various Boost/Buck converters that are present in the modules. The fault could be a component failure that is leading to an overload of the 5V supply rail.

I did a quick check across the 4V8 Ni-Mh pack and was surprised to see it alternating between 4V94 and 3V6. Something nasty is going on. The rail cycles in sync with the TAU trying to Boot and I know the TAU current draw is correct. Something may be causing an over current event soon after camera power is applied. It is just a case of tracking down the guilty component  It could, of course be a poor connection in the sealed battery bay so that will be checked fist by replacing it with a current limited  bench power supply.

All good fun.

Fraser   

[Fraser]

As the TAU core is now fully functional again, I will end my commentary here as this is a thread dedicated to the TAU core and not the FLIR HS324.

I have another live thread covering the HS324 so will post any repair information on the HS324 chassis there.

https://www.eevblog.com/forum/thermal-imaging/flir-hs324-commander-thermal-camera-teardown-by-fraser/

Fraser

[Chanc3]

Thrilled you managed to get it working! and loved the process you took. The cores are very nice little IR cameras, although they are not very user friendly unless you have a special board connected to save the images etc. We ended up using a 3rd party control board to give us full radiometric images and video, for when we mount it on our UAVs.

[Fraser]

Hi Chanc3

Yes I have seen those UAV add-on modules. Very nice

The Tau appears to be a pretty versatile little core that receives good support in the UAV community.

I am very pleased to have brought the little Tau back to life. If I were to have the time again, I would do things a little differently though.  I was too eager to dive into the Tau on this occasion. The benefits of hind sight eh

I did learn quite a lot about the Tau architecture and power supplies though.

Fraser

[ry21]

Wow! There is one thing that confusing me. I don't see any high-speed ADC on the pcbs and it means, I guess, that the FLIR bolometer sensor has a digital video output? 

[Fraser]

Modern Microbolometers have moved to integrated ADC's on the ROIC

Take a look at the ULIS web site and products for a view of current technology. The microbolometers 'on board' ROIC is getting 'smarter' and more heavily integrated with every generation.

Fraser

[Tomas]

Hi do you have this bord in spare?   

[Fraser]

Hi,

Sadly I do not have a spare board. The TAU interface board belongs in my FLIR MS224 scope and will eventually return to it when needed.

Fraser

[Ultrapurple]

Modern Microbolometers have moved to integrated ADC's on the ROIC

Take a look at the ULIS web site and products for a view of current technology. The microbolometers 'on board' ROIC is getting 'smarter' and more heavily integrated with every generation.

Fraser

Do you foresee a time when the ROIC will include things like a NUC stage followed by whatever output you want (digital video, data stream, LCD drive, PAL...)? It's a fair degree of integration beyond the present state of the art (as far as I know...) but, I suppose, possible.

[Fraser]

The latest ULIS offerings integrate many functions into the ROIC But they are not a 'camera on a chip' solution yet. The Lepton core is getting closer to what you describe. There are issues with a thermal camera on a chip as any form of true processing power on the imaging array die would generate heat. Die self heating is the enemy of thermal FPA's. Any design that placed any serious processing power on the imaging die would need to find a way to thermally isolate the heat sensitive structures from the heat sources. This would need to cope with conducted, converted and radiated heat energy. I see it more likely that we will see sandwhich designs that keep the thermally sensitive components physically separated from the heat producing processing elements by a thermal break. Active temperature stabilisation has been around a long time and these can help keep the die at a reasonable temperature. The downside of Peltier stabilisation is current consumption and bulk as a heatsinks is needed to dissipate the heat produced.

The Raytheon Thermal Eye 2000AS and its descendants are the sort of topology I see as the most versatile. The sensitive imaging microbolometer sits on the back of the lens module and links to the heat producing processing engine via a ribbon cable. Good thermal isolation is relatively easy to achieve in such a design.

Fraser