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| TC1 lcr-meter transistor-tester fix |
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| TurboTom:
@masster: I'm not questioning your repair success. But I would really like to understand the undisputable findings that in your thermal image, the microcontroller heated up while this cannot be clearly told for the capacitor. The thermal part of your image is too far out-of-focus to tell. I assume you took the images with a FLIR ONE or a similar device which has the thermal and the optical cameras installed side-by-side, so at close distance you've got a parallax error. The wide angle optics will result in this problem to vanish at higher distance. Moreover, there may be some active correction for this parallax error built into the thermal imager's software. FLIR's more recent cameras offer an optical overlay mode that they call "MSX" which is enabled by default. And that's contributing the apparent in-focus structures in your thermogram. Try disableing MSX display mode and experiment a little with your TIC. If the replacement of the apparently shorted capacitor C7 (and maybe the 5V linear voltage regulator) brought your TC1 back to life as you reported, and the microcontroller no longer heats up, the only explanation for this is that the designer of this PCB made a bad error: He may not have connected all the supply lines of the ATMEGA to Vcc individually and have the node where C7 is attached floating. This means, C7 will buffer this supply line but power will flow over the metallization of the ATMEL's die. And if C7 shorts this supply, this metallization layer can well become a heating element. It would be interesting to check that on the current TC1 version's PCB... As I reported before, my TC1 is of the previous design with the single voltage converter and the transformer. Depending on the ruggedness of the ATMEGA die and the current limit of the voltage regulator, this may or may not cause permanent damage to the microcontroller. That's IMO the only reasonable explanation that a shorted capacitor C7 may result in the microcontroller to heat up. |
| MarkMLl:
I'm just about to lob one of these into the spares bin, I've spent more time on it than it's worth. However, a couple of comments if I may: The PCB is as shown in Kamlakkannan's #78 with silkscreened "LCR-TC" and "XR-112" markings, and an unpopulated 8-pin outline next to the ISP header position. C11, 12, and 13 appear to be in roughly the same place and have the same function on all boards discussed (all appear good in my case). C6 and in particular C7 appear to vary. On my (and most) boards they're associated with U4 (8-pin chip probably STC) while on the board discussed by Masster C7 is associated with the Atmega's pin 38 (Vcc). I agree with the points made by various people about the parallax error between the optical and IR optics on IR cameras. I'm surprised that there isn't an offset table, either on the side of the camera or at least in the manual. MarkMLl |
| PcarSBA:
Hi, I blew up my Atmega324 based TC-T7-H transistor tester by connecting a 470uF capacitor charged to 5V to pin 1 and 3 |O It took out the TVS diode array. With it removed the Atmega324 comes on again but I get the dreaded 4.1V cell voltage between 1 and 3. Pin 3 has 56Ohm to Vcc. And that resistance remains with it lifted off the PCB when measuring the pin directly to Vcc. So I conclude that I need to replace the Atmega. Can someone help me decide what version of main firmware I should or can install onto the new Atmega324. I read through a lot but am still not clear as to whether I also need to change firmware on the STC15W104 when I pick one of the versions of Github? Thanks for any help |
| abdulbadii:
original C is non polarized C isn't it, how can be replaced by polarized one? |
| madires:
--- Quote from: PcarSBA on January 09, 2023, 06:47:27 pm ---So I conclude that I need to replace the Atmega. Can someone help me decide what version of main firmware I should or can install onto the new Atmega324. I read through a lot but am still not clear as to whether I also need to change firmware on the STC15W104 when I pick one of the versions of Github? --- End quote --- If you want to run one of the two OSHW firmwares you need also to reprogram the STC15W104 or replace it with a simple 2-transistor circuit. |
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