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[time-freq] Some interim construction notes for RefLock II

Christopher T. Day CTDay at lbl.gov
Fri May 19 21:13:30 UTC 2006


I've just finished the construction of my RefLock II kit and have fed my
notes to the manual writer. In the meantime, I'm posting them here in
raw form as them may be of some help to people holding back on this cool
kit. I hope they are of some use.

 

 

 

            Chris - AE6VK

 

P.S. - I don't know how to do this other than paste the text in here. My
apologies for the verbiage.

 

 

Tool suggestions:

 

A magnifying lamp or equivalent. The parts and silk-screen markings are
quite small.

 

A pair of tweezers with sharp points and a soft squeeze. Check local
cosmetic boutiques. If the tweezers are too stiff, there will be a lot
of energy stored in them while you are trying to manipulate tiny parts;
a slip will send the part flying into oblivion.

 

Some kind of "third-hand" to firmly hold the circuit board while you are
soldering parts. I used a Panavise with circuit board holder head.

 

One, preferably two, sharp tipped 15W soldering irons. I got mine at
RadioShack.

 

In a few cases, 15W will not supply enough heat so something bigger will
be needed. I used a small 100W soldering gun; I would be careful going
to higher power, and 50W is probably sufficient.

 

A non-clean flux pen is handy. I found a Kester #951 pen at my local
RadioShack.

 

Keep the tweezers non-magnetized and the tips clean of adhesive from the
parts pages. It can be frustrating to place the part perfectly and then
not be able to let go of it.

 

Keep the soldering iron tips sharp, and clean with a damp sponge, cloth
or paper towel.

 

Use anti-static precautions. Ground yourself just before touching
components, or use a grounding wrist strap. The CPLD at least is static
sensitive.

 

For soldering techniques, I basically followed the procedures described
at http://www.tapr.org/~n7hpr/dsp-10. I particularly like the twin
soldering iron technique for handling SMD resistors and capacitors. One
modification I made to the process was to put down some flux _before_
tinning the pad and placing the components. The parts in this project
are smaller than those on the DSP-10, and these tend to stick to the
flux pen.

 

It should take no more than a second or two with the irons to melt the
solder for each of the small parts. Don't linger as the small pads will
delaminate if too much heat is applied.

 

 

Notes on parts and silk screen outlines:

 

Because of the flexible nature of the hardware defined inside the CPLD,
you are not actually building a specific device at this point. It will
only be complete when the configuration file is downloaded. To maintain
flexibility for the contents of that configuration file, there are
various hardware options available on the PCB; not all of them are used
in most cases.

 

One option is a prescaler for use with VCXOs above about 250MHz. On the
assumption that most users will not be controlling an oscillator that
high, parts are not supplied in the kit for the prescaler, viz., there
is no U2, R20, R21, or C19-C22.

 

The note on the schematic Sheet 2 near the left edge of the page is
incorrect. It should read "NOTE; populate R17 only if Reflock VCXO IN
requires 50ohm termination.", so this is another part you might not use.

 

Three I/O pins of the CPLD are available for configuration files to use
to output the VCXO control voltage. You will choose one of these with a
0 ohm jumper at PD1, PD2-N or PD2-I, depending on the configuration file
you choose and the hardware you are controlling. Do not install any
jumpers here at this point.

 

Similarly, the pads along the bottom edge of the PCB are available for
supplying binary configuration data to whatever configuration file is
loaded. Do not install any 0 ohm jumpers here - they would go on the '0'
pads - but DO install R32-R49, one on each of the '1' pads.

 

 

Construction:

 

You will probably have to use a zoomed copy of the silk screen PDF file
to locate where the components go; the resolution of the text on the
silk screen is sometimes marginal. R32-R49, as mentioned above, go on
the '1' pads across the bottom of the board; they are not otherwise
labeled.

 

Install the parts in order from the Parts Sheets, but skip the 20 0 Ohm
"resistors" to start with. They will be installed later to configure the
CPLD file you eventually load.

 

Finish all components of a given value before moving on to the next
value. The resistors are actually marked with their values in very small
type, but the capacitors have no clue on them as to their value. If you
have several different values out of their packing strips at once, good
luck sorting them out.

 

The resistors and ceramic capacitors are unpolarized, so can be placed
in either orientation on the board.

 

The larger tantalum capacitors _are_ polarized. Be sure that the end of
the component with the line across it goes to the pad with the '+' sign.

 

The LEDs are also polarized. There is a very small colored dot on the
edge of the LED near one end. Be sure this end goes on the pad with the
small white dot near it on the silk screen.

 

For the transistors, I found trying to work with two soldering irons
awkward. Instead, tin only one pad, tack the transistor in place at this
pad, then solder the other two pads.

 

Use a similar technique for U3. Remember that U2 is optional and not
included in the kit.

 

Once everything from the parts sheets except the 0 ohm jumpers has been
installed, take a few minutes to check carefully that the parts are all
in the right place and have no obvious cold joints. Then start
installing parts from the envelopes.

 

When you install the 10 turn pot, once it is seated against the PCB
board, vertical and soldered into place, trim off the excess leads from
the back of the PCB.

 

All the headers are polarized. For the white headers, be sure the white
tab matches the small box on the silk screen. For the black JTAG header,
be sure that the side with the slot in the _center_ of the edge faces
_away_ from the edge of the board. [Note that the kit includes parts to
make up cables to plug into the white headers; these are the other white
things without pins, and all the little crimp-on clips.]

 

Install the four coax connectors in two phases. First, using a 15W iron,
solder the center pins to the PCB. Make sure the connectors are snug
against the PCB and vertical. This can be done by setting the four coax
connectors upside down on your bench and setting the PCB face down over
them; you will probably have to hang the 10 turn pot over the edge of
the bench to keep things level.

 

Once the center pins of the coax connectors are soldered, bring out the
higher powered iron and solder all the corner pins. Work quickly so as
not to overheat the PCB.

 

Finally, install the regulators as follows: Match the voltage rating of
the regulator to the silk screen marking at the white header below the
regulator. _Before_ soldering the regulators, apply a uniform, thin
layer of solder to each of the large pads at the regulator positions
using the 15W iron. Then solder the pins only of the regulators, again
using the 15W iron. Finally, using the more powerful iron, heat the
metallic heat sink's top edge on each regulator while pressing down
firmly on the face of the regulator. Watch for the solder you added to
the pad to melt and squeeze out from under the heat sink. At that point,
remove the iron but maintain the pressure until the solder solidifies
again. You don't want to leave gaps under the heat sinks as that will
lower the power that the regulators can handle.

 

Check again carefully for missing parts and cold solder joints. Fix
what's needed and you should then be ready to configure your CPLD and
decide what hardware you've really built.

 

 

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