JYE Tech Forum

Hello.

Today I defeat the subj problem. The culprit was C14 capacitor 0,1 uF. It's resistance, when measured directly in the circuit was only 28K. C14 is in parallel of RESET button, and MCU was in constant reset mode. I delete C14 and everything became ok.
If you have the same problem, measure resistance of C14 directly in the circuit. It must be ~1,8M...2,3M. If no - delete C14.
I spent several days searching for a reason and even tried to change the MCU to another, but this, of course, did not help.

Just in case I give you the table of resistances between GND and MCU pins in a GOOD oscilloscope. Measured with NO display, all switches are in the center position, NO power supply. Hope this can help you to defeat difficult problems.
1 - 800
2 - 12,3M
3 - 12,3M
4 - 12,3M
5 - 1M
6 - 1M
7 - 2,2M
8 - 0
9 - 800
10 - 1,2K
11 - 4K
12 - 4K
13 - 4K
14 - 920K
15 - 920K
16 - 1,7K
17 - 960K
18 - 950K
19 - 950K
20 - infinity
21 - infinity
22 - infinity
23 - 0
24 - 850
25 - infinity
26 - infinity
27 - infinity
28 - infinity
29 - 102K
30 - infinity
31 - infinity
32 - infinity
33 - infinity
34 - 10K
35 - 0
36 - 830
37 - 10K
38 - infinity
39 - infinity
40 - infinity
41 - 1M
42 - infinity
43 - infinity
44 - 1K
45 - infinity
46 - infinity
47 - 0
48 - 830

What voltage does your multimeter present to the circuit under test on the highest resistance range?

Dave

davef wrote:What voltage does your multimeter present to the circuit under test on the highest resistance range?
Dave

It's about 0,55V. Multimeter is automatic.

OK checked my two DVMs and they are about the same. If someone grabs a old analogue multimeter to do these measurements they might want to check whether or not the meter will put excessive voltage on the chosen resistance range.

Cheers,
davef

MegaVlad wrote:Hello.

Today I defeat the subj problem. The culprit was C14 capacitor 0,1 uF. It's resistance, when measured directly in the circuit was only 28K. C14 is in parallel of RESET button, and MCU was in constant reset mode. I delete C14 and everything became ok.
If you have the same problem, measure resistance of C14 directly in the circuit. It must be ~1,8M...2,3M. If no - delete C14.
I spent several days searching for a reason and even tried to change the MCU to another, but this, of course, did not help.

Just in case I give you the table of resistances between GND and MCU pins in a GOOD oscilloscope. Measured with NO display, all switches are in the center position, NO power supply. Hope this can help you to defeat difficult problems.
1 - 800
2 - 12,3M
3 - 12,3M
4 - 12,3M
5 - 1M
6 - 1M
7 - 2,2M
8 - 0
9 - 800
10 - 1,2K
11 - 4K
12 - 4K
13 - 4K
14 - 920K
15 - 920K
16 - 1,7K
17 - 960K
18 - 950K
19 - 950K
20 - infinity
21 - infinity
22 - infinity
23 - 0
24 - 850
25 - infinity
26 - infinity
27 - infinity
28 - infinity
29 - 102K
30 - infinity
31 - infinity
32 - infinity
33 - infinity
34 - 10K
35 - 0
36 - 830
37 - 10K
38 - infinity
39 - infinity
40 - infinity
41 - 1M
42 - infinity
43 - infinity
44 - 1K
45 - infinity
46 - infinity
47 - 0
48 - 830

You tried the published solution and it worked perfectly for me. Replace the capacitor with a new one (C14)