18F46K20 2x PCBs 1x works the other doesn't

Thread Starter

camerart

Joined Feb 25, 2013
2,771
Hi,
I have two identical?? PCBs with Crystal controlled 18F46K20 PICs
One of these boards, doesn't fire correctly. The Crystal is working fine. I've checked all of the relevant? tracks.
It should output a serial signal via a radio link, and there is a LED flashing each LOOP.
The reult is: I can hear the radio on a listening radio, but it is sparodic, along with the LED.
Any ideas please?
Camerart.
 

trebla

Joined Jun 29, 2019
470
Check decoupling capacitors and MCLR pull-up resistor. Usually this kind of behavior is caused by inconsistent or noisy power supply lines.
 

Thread Starter

camerart

Joined Feb 25, 2013
2,771
Check decoupling capacitors and MCLR pull-up resistor. Usually this kind of behavior is caused by inconsistent or noisy power supply lines.
Hi T,
I had checked the MCLR pull up, and gone round the CAPs, but it does look like that sort of thing.
I noticed the tracks aren't the best, so I'm going to make another PCB, and go from there.
C
 

Thread Starter

camerart

Joined Feb 25, 2013
2,771
Hi,
I've found the problem :)
It was the wrong PIC :rolleyes:After checking 'everything' a 100 times, I found the PIC was an 18LF4620, so I changed it to 18F46K20, and now it's firing ok.
Thanks.
C
 

cmartinez

Joined Jan 17, 2007
7,525
Hi,
I've found the problem :)
It was the wrong PIC :rolleyes:After checking 'everything' a 100 times, I found the PIC was an 18LF4620, so I changed it to 18F46K20, and now it's firing ok.
Thanks.
C
I bet it was one of those head-banging epiphanies that one never forgets afterwards ... some lessons are a PITA to learn, but the experience sticks for life.
 

Ian Rogers

Joined Dec 12, 2012
952
Hey C.. don't feel bad... I had an I2C 24lc256 soldered into an SPI 25lc256 position... Couldn't see it for love or money.. I tried everything... A younger pair of eyes found the fault.. In my defense, they were in the wrong bin..
 

Thread Starter

camerart

Joined Feb 25, 2013
2,771
Hey C.. don't feel bad... I had an I2C 24lc256 soldered into an SPI 25lc256 position... Couldn't see it for love or money.. I tried everything... A younger pair of eyes found the fault.. In my defense, they were in the wrong bin..
Hi P and I,
I don't feel bad, but from experience, I mostly know, a fault is usually something my end, so I keep checking, and those digits need a lens to check them. And I have done it before.
C
 
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