[time-nuts] FE5680A

[Rich]

This is my first post here. Unfortunately I found this informative group a
bit late.

I got from e-bay a similar unit to yours with an identical pin-out from the
e-bay listing. As in your case I did not get a 1pps output and there were no
lock indication although the 10MHz initially wandered and after 5 min or so
it locked.

I opened to unit and traced a good part of the circuit with the aid of about
25 high resolution x-rays of the board. I mounted them on a wall in my
workshop and created a composite high def x-ray about a yard across. This is
excellent to follow traces below the ICs and in the board layers and vias.
Don't know if I can post attachment but I'll try one to give you the idea
with a jpg of the layout. Should people be interested I can post all of the
25-30 x-rays of the pc board on a website for those who would like to trace
or troubleshoot the overall circuit without having to remove the chips.

Finally found the Fairchild 74ACT240 to be the culprit. It was pulling down
the lock circuit and preventing the 1pps from coming out. Seller must have
damaged it and that is why it was at a such low price I guess.

I now use a 330 ohm resistor in series with a LED and the lock indicator
work fine and well as the 1pps.

As to the RS-232 I get a response using 960 n 8 1 as outlined in these
forums. Did not dare changing the frequency yet until I get a higher
precision setup that will actually measure the change. No quite there yet.

Hope this is useful for some of the members.

Richnormand
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