开云体育

I'm working on a QMX for someone. The display is showing one row of black rectangles. I assume that means the display and the microcontroller are not communicating as in the QCX. The unit is drawing about 50 mA more than expected in receive mode and the microcontroller is getting very warm to the touch. The device is showing up on Putty and firmware is successfully loaded. It even is recognized in wsjt-X and CAT test is green, so it seems that most of the ?microcontroller functionality is good. I have good continuity from all LED display pins to their respective pins on the microcontroller BUT I am seeing a short to ground on pin 5 of the microcontroller which is connected to LCD D6. The short is still there with the display board removed. Can someone verify for me that there should NOT be a ground on that pin? I don't see any obvious shorts external to the microcontroller chip. Thanks ... Ron

Hi Ron,

That pin 5 should not be shorted to GND. ?I always use a milliohm meter to try to find the precise location of a short. ?Maybe it’s within the processor or along the pc trace somewhere. ?I replaced a cpu in a QMX that had one pin shorted to ground but was otherwise ok. ?In my case it was pin 26. ?Replacing the cpu with a cpu from a donor board fixed the problem. ?Good luck.
Jeff
W1NC

Hi,
yes, you need the pin LCD D6 to be off GND.
Perhaps you can follow the path as in the attachment and look under the microscope for the short.
And hope that the pin 5 has survived.

73 Bojan S53DZ

Thanks Jeff and Bojan. I found the cause of the short. The builder repaired what was thought to be a ?broken trace on top of the board, below one of the regulator boards but this caused a short to ground on this pin when doing so. I now have a good display and 50 mA less current draw. I appreciate the helpful comments. 73...Ron