Strange issue with 328p-pu

Hi all, This will be my first post, but I've been reading the forum's for quite some time. I'd like to thank everyone in advance for all the things I've learned on these forums. This one has me stumped.

I purchased a few atmega328p-pu chips on ebay, supposedly with the bootloader preloaded on them.

I hooked them all up to the breadboard (one at a time of course) per the instructions on this site as I have with other chips in the past.

These chips however appeared to not be working.

After playing around with them for a bit, I realized that if I plugged the 16mhz crystal into the xtal ports, the blink script was working... however if the 2pcs- 18-22pf caps are connected to the crystal, and ground as they should be, the chips stop blinking and I can not program it or bootload it.

If i pull the crystal, the chip stops blinking. If I put the crystal back in, with no caps, the chip will blink again. Basicly it works without the caps, but not with them.

If I hook it all up with just the crystal .... I can load a bootloader and program the chips using my uno as an isp.

I have tried programming and bootloading them with the correct setup (having the capacitors installed along with the crystal) and I get the dreaded YIKES Invalid device error from avrdude every time. Pop the crystal in without the capacitors and I can communicate with them again.

Is it possible that these chips were bootloaded with just a crystal and somehow the fuses are set wrong?

If so, can I clear them out and program them correctly?

Is my oscillator even capable of generating 16mhz freq without being grounded? (seriously).

This has been driving me bonkers. Any insight would be appreciated. Thanks in advance.

You are using a breadboard, aren't you?

The breadboard is the 22 pF caps!

When you add caps, the capacitance is excessive.

Paul__B: You are using a breadboard, aren't you?

The breadboard is the 22 pF caps!

When you add caps, the capacitance is excessive.

I'm not quite sure I follow you. I am using a breadboard. I've always used the 22pF caps in the past with the breadboard and never had a problem. Every "Arduino on a breadboard" tutorial I've ever seen has the 2 - capacitors linked between the crystal and ground. Could you elaborate a bit?

Others have used wrong capacitor values thinking they were 22pf. What is written on your capacitors?

@Paul__RB 2-3pf https://www.youtube.com/watch?v=6GIscUsnlM0

LarryD: Others have used wrong capacitor values thinking they were 22pf. What is written on your capacitors?

Hi Larry, the I've tried caps marked 22, and ones marked 104... neither work.

Show us a picture of your circuit with the capacitors installed. Also, a picture of the 22pf caps, both sides.

104 is wrong for this application!

Well, I think I figured it out. Thanks to the video link you left for me Larry. Paul, you were on to it. After watching the eev blog video, I broke out my cap tester and sure enough, between the crystal and ground on my board it measures 22 to 25pF.

I guess I'm going to have take that into consideration in the future. Is this measurement based on the number of components on the board? I may have to play around some more and experiment with my capacitance tester. Thanks for the help guys. :)

No, it’s just those long spring strips in parallel with dielectric separating them. And of course, ground is directly adjacent to Xtal1.

Behaviour may depend on the allocation of “pin 5” which is also adjacent - whether it is defined as an output or input, and to what it is connected.