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$20 LCR ESR Transistor checker project

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indman:

--- Quote from: bffargo on January 10, 2022, 03:39:54 am ---I am having a problem with a new GM328A (red pcb) kit.

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In this topic and the author's manual repeatedly reiterated condition, which solves 99% of all problems with measurements and calibration, replacement of the weak Chinese +5V regulator to a QUALITY (MCP1702, LP2950)!

bffargo:

--- Quote from: indman on January 10, 2022, 07:29:28 am ---In this topic and the author's manual repeatedly reiterated condition, which solves 99% of all problems with measurements and calibration, replacement of the weak Chinese +5V regulator to a QUALITY (MCP1702, LP2950)!

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--- Quote from: Yuriy_K on January 10, 2022, 07:08:57 am ---I had a similar issue when upgrading from 1.12k to 1.13k. The problem is in the 7550 and the capacitance of 10 microfarads, to the right of the crystal. Change the 7550 or match the indicated capacitance with a large ESR within> 3 ohms

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I swapped the capacitor, the 7550 and the TL431 between boards and the problem stayed with the board. I then replaced them all with other parts and the problem again stayed with bad board and the good board still worked fine with parts from the bad board.

Any other ideas as to the source?

Yuriy_K:

--- Quote from: bffargo on January 13, 2022, 01:17:11 am ---Any other ideas as to the source?

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Compare the selftest run on your boards with the picture:

Feliciano:

--- Quote from: bffargo on January 13, 2022, 01:17:11 am ---Any other ideas as to the source?

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Besides the Atmega or the ZIF socket (it can be bypassed for tests), other user found a bad PCB with a tiny shortcircuit among traces, and we have found some shorted ceramic capacitors too (SMD and/or through-hole).

bffargo:
As stated in the original post, ATMEGA was swapped between boards and problem stays with board; the microcontrollers are healthy in the other board.

ZIF socket bypassed for SMD pad but same results.  Show 0 ohm continuity between all pad and zif pins as well no cross shorting there. 

All resistors measured in circuit with ATMEGA removed and show in spec and same between boards within ~1%. 


Edit: I pulled every transistor (except the LED one ) and every capacitor and tested and swapped between boards. Still same problem that always stayed with the bad board.

Could not see any damaged/shorted traces anywhere.  Metered for shorts in the microcontroller socket and ZIF and found nothing.  I'll do a bit more digging then get config data.  Thanks.

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