Repair of a high resolution thermal imager (IRC-640ca)- No analog output - Page 1
Forum section: electronics / repair

author: Westcoastweenie
author_rank: Newbie
timestamp: June 14, 2025, 01:55:04 am
content: Hi there everyone, i hope I'm posting this correctly as i am a first timer here... I apologize in advance if I've mixed something up. In any case, I picked up a used thermal imager and unfortunately, the unit is DOA. After a week of poking and probing, i think I'm in need of some advice from those with far more experience than me. I'm most certainly out of my depth with this.When initially testing it, the power draw is roughly correct, the shutter operates as it should and closes when recalibrating to different heat sources, so i am hopeful the camera itself is still functioning. However the analog output is totally dead, just noise from my benchtop power supply is measurable.One possible hint, there was a small ferrite core inductor that had burnt varnish. In the photos it has been removed as I'm trying to figure out its values for replacement... that will probably be another post in itself lol.I've attached some photos with some annotations on what's going on to the best of my understanding so far. Unfortunately i lack a solid fundamental understanding of circuits and don't really know where to go to find relevant information on analog video systems like this. I've been searching for about a week but i may be a really poor googler, so it has been slow going.It seems that the only electrical path between the video out on the TV encoder (DAC) and the CVBS output wire was that burnt inductor. With the inductor removed, the yellow wire to DAC output measures open circuit while Ground wire to the DAC out was reading closer to 0.5 ohms. I have to assume the only path between the DAC and video out wire shouldn't be a filtering inductor, given its a high frequency signal. I'm also guessing that the inductor is supposed to be the only link between analog out and ground, which is currently not the case. Or maybe I'm wrong on both assumptions as my electronics repair skills previously ended at small appliances and audio equipment.If the consensus is that the analog section is probably un-salvageable, a last effort would maybe be tapping into what i think is a usb header. I was able to see some kind of pulses on 2 of the 4 pins with an oscilliscope while the others were voltage and ground. Im not sure if anyone else on here has played with the digital out one of these units before, but if someone has, id love to hear about if it can be done and if so, how to make it all work.Thank you in advance everyone, any advice or wisdom is well appreciated. I want to give it everything I've got before throwing in the towel.

author: m k
author_rank: Super Contributor
timestamp: June 22, 2025, 07:24:41 pm
content: CVBS output can't be GND if you want a picture from it.

author: Westcoastweenie
author_rank: Newbie
timestamp: June 23, 2025, 08:12:19 pm
content: Thanks for the reply, im glad to hear the cvbs pin should not be tied to ground. That gives me a good starting point to follow traces out from the cvbs pin, so its much appreciated.Would you happen to have a guess on what components may run between cvbs and ground under normal operation, other than the inductor? I was guessing maybe a diode with a low breakdown voltage to protect against connecting things backwards (swapping v+ and cvbs)... Or some other components that achieve the same protective task. Im not sure what else that would be.Thanks again.

author: m k
author_rank: Super Contributor
timestamp: June 24, 2025, 08:28:54 am
content: Not much.Reverse diodes are not very usual as external components.https://www.labguysworld.com/VideoCookBook_005.htmhttps://www.analog.com/en/resources/technical-articles/video-signal-distribution-using-low-supply-voltage-amplifiers.htmlhttps://www.analog.com/media/en/technical-documentation/application-notes/an57fa.pdf

author: Gyro
author_rank: Super Contributor
timestamp: June 24, 2025, 11:54:44 am
content: You might want to report yourself to the moderators (use the Report to moderator link, bottom right) and ask politely for this thread to be moved to the Thermal Imaging section. You're more likely to get help there and it might not be noticed by the folks here.Do it that way rather than starting a duplicate thread there as double posting is frowned upon.

author: Westcoastweenie
author_rank: Newbie
timestamp: June 28, 2025, 06:04:32 am
content: Thank you for the links! They look like a great place to start gaining a better understanding of what I'm actually looking at here. Much appreciated.

author: Westcoastweenie
author_rank: Newbie
timestamp: June 28, 2025, 06:06:45 am
content: Will do Gyro, thanks for the tip. I only noticed the thermal imaging section after posting here and figured it may have been a bit of a faux pas to double post.

author: AlexKr
author_rank: Newbie
timestamp: September 22, 2025, 08:34:55 pm
content: Hello. I didn't find this topic in another thread. Did you manage to solve the problem? I'm facing the same issue - no image on the video output.

author: Westcoastweenie
author_rank: Newbie
timestamp: October 02, 2025, 02:42:53 pm
content: It never got moved unfortunately and since then life got in the way so ive shelved the project until later this fall. Ill be making a new post in the thermal imaging section of the forum sometime in late october when crops are harvested and the time frees up.If its of any help, after some more digging a while back, i found the sensor appears to be made by GSTiR, and is the GST612c (or GST412c if its a 384 sensor). They might sell a bare interface board for cheaper... I havent tried yet.If you made any headway on repairs yourself, id love to hear about it.