Re: what else to do before pronouncing IC2 dead?


scot forshaw
 

I have seen this for many reasons related to the ATmega CPU and the LCD. The LCD is testable on breadboard with a spare Arduino board. 

The CPU May be loose in socket, bent pin hiding underneath (really common)

Hey here’s
Scot
2E0WWV 


On 27 Aug 2020, at 06:16, Mike KK7ER <groupio@...> wrote:

After finishing construction of the QCX+, I have the "row of black squares" issue.
I followed the troubleshooting section and read through various group messages.
I traced all the relevant pins from IC2 to the display board header using an ohm meter:

IC2-2      LCD D4  JP4-5     DispHeader 11   continuity good

IC2-3      LCD D5  JP4-6     DispHeader 12   continuity good

IC2-4      LCD D6  JP4-3     DispHeader 13   continuity good

IC2-5      LCD D7  JP4-4     DispHeader 14   continuity good

IC2-6      LCD EN  JP4-1     DispHeader 6     continuity good

IC2-8      GND                                                continuity good

IC2-20   AVCC                     R61-1                 continuity good

IC2-22   GND                                                  continuity good

IC2-27   LCD RS  JP3-4     DispHeader 4     continuity good

Sadly, I do not have an oscilloscope.
I measured voltages with a volt meter while the rig was powered up:

IC2-1      not(RESET)                                    4.38V     chip not being held in reset

 

IC2-2      LCD D4  JP4-5     DispHeader 11   4.90V

IC2-3      LCD D5  JP4-6     DispHeader 12   4.90V

IC2-4      LCD D6  JP4-3     DispHeader 13   4.90V

IC2-5      LCD D7  JP4-4     DispHeader 14   4.90V

IC2-6      LCD EN  JP4-1     DispHeader 6     0.00V     LCD is disabled???

IC2-7      VCC                                                 5.00V     correct supply voltage
IC2-27    LCD RS  JP3-4     DispHeader 4     3.55V     LCD is being held in reset???

I checked if LCD EN was shorted to ground and it was not.  I also checked to see if any data pins were shorted together and they were not.

Assuming the sense of LCD EN and LCD RS are as marked on the schematic, IC2 is disabling the display and holding it in reset.  That does not seem like proper behavior if IC2 has booted and it executing code.  While I realize that volt meter measurements on serial data lines is inconclusive at best, it sure seems that there is an issue with IC2.

What else should I test before ordering a replacement?

73, Mike KK7ER

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