Quote:
Originally Posted by byteoftce
Your last post might contain the solution. But I prefer to ask again. Are you sure the C11 and C15 must have 22Pico? According to the BOM list (Github), C15 is specified as 100 pico....
edit:
I think I found the mistake. The reference to C11 was entirely correct. I love our Chinese, who seem to be up for a joke from time to time. Instead of 22pico, they labeled a capacitor strip with 220pico capacitors as 22pico. Someone probably thought binary 0 or 1 (220 or 221 ...). Oh, that's right ^^.....
Now that I've replaced C11, it also works with fixed resistors. R3 with 4.7K -> J2 2.6V- Almost perfect....
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You fixed it! Yeah, 220pf is definitely too much and will make the PLL loop unstable. I am very happy to hear that your card now works as it should.
Also, you're right, C15 must be 100pf. Sorry for the confusion. It probably also works with 22pf but 100pf is best. My first prototype had no C15 at all and that worked not so well. Due to the weak signal level of the Amiga's 7Mhz clock the phase comparator produced a very jittery output. With capacitive coupling the phase comparator biases itself and the output is then (well, almost
) jitter free. PLL's are always tricky and I spend quite some time to make make it work proper.