[time-nuts] Reverse Engineering the FE-5680A and how to take it apart (was: Determination of the placement of the first pps)

Attila Kinali attila at kinali.ch
Wed Jan 25 18:21:46 EST 2012

On Wed, 25 Jan 2012 20:19:16 +0100
Magnus Danielson <magnus at rubidium.dyndns.org> wrote:

>  Reverse-engineering the schematics and functions has only 
> partly been done, but I haven't seen any systematic schematic popping 
> out of the work.

Now that i have received my units, i thought could help with the
schematics. But having had a look at mine, i dont think it's worth
the effort. The PCB has at least 4 layers, more likely 6. I don't
think it's 8 as the PCB looks cost optimized.

A few distinct subsystems can be identified by their position, but
their connections and the connections within are hard to get. It would
take countless hours with good measurement equipment to get anything
halfway usable.

I'd rather say, save the time, buy another spare unit if you think
one of those you have is going to fail.

For those who wants to open their unit here a few hints:

* Unscrew the unit from it's base plate
	They are either Torx or Hex. But this doesn't matter at this size,
	the difference is hard to tell and is very small anyways.
	I used a T6 Torx screw driver, as that was what i had at
	hand that did fit. Be carefull, the screws are cheap and very
	soft. It's easy to rip the torx/hex bit apart. Apply ample pressure
	to your screw driver.
* Unscrew all screws that you can see from outside
	* two in the center of the bottom plate
	* two underneath the DB-9 connector
	* two on the side of the DB-9
	* two on the sides
	These are Philips-1 and Philips-2 screws
* There is a screw under each lable at the top
* After this, you can take the unit apart. The heat spreader in the middle
  comes out together with the PCB
* Do NOT force the PCB out. If you need to, wiggle gently. If you have
  to use force, you've forgotten a screw.
* The two screws that you see on the PCB stay there (they hold the PCB
  on the head spreader). I do not recommend to unscrew them.

* Take lots of pictures while you are at it :-)

If possible, i'd be interested in two Revision markings on the PCB.
Mine has a sticker at the bottom, that reads "RevF".
Then there is a PCB number on the top side, at the edge near the
reference crystal (that with the PTC soldered to it). My unit reads there
"217421-30352" "Rev G"

			Attila Kinali

Why does it take years to find the answers to
the questions one should have asked long ago?

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