I have a number of systems that work, enumerate, and function. And I have another number that does not even attempt to pass data to the host. Using a protocol analyzer it immediately tells me "device problem". I'm using 1/2 watt diodes and 68 ohms for my - + leads. I also have a 1.5k pull up on +. This is a atmega168 so I need the 1/2 watt diodes. Most of the troubles are on newer systems and I think mostly 2.0 ports ( more so in laptops ). Although most computers have 6 ports or more and if it fails on one port on a system it fails on all of its ports, likewise if it works on one port on a system it works on all of them.
Also in the cases where it fails, if I plug in a hub ( in between ) it works. I matched the device descriptors of the ports and I see no differences.
----
Ok I ruled out the diodes.. I found an old board and was able to make it work. I tried switching out the diodes on the trouble board and that didnt help. I would not think the 12mhz caps would matter. The 12mhz is identical. and all 3 resistor have the same value. I'm so confused on this one.
-------
Ok turns out it was the diodes. Note sure where I failed to test that the first time... The surface mounts produce 4.0 and my regular through hole shows 2.7 .. something weird there..