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FM-100 Page 34
These capacitors give the crystal the proper loading so that it operates on
the correct frequency. In the FM band, our crystal can be off by as much
as .01% and most tuners will pick it up just fine. As this crystal is set up, it
will be within .001%, which is 10X better, and that’s without tuning!
55G. Install C34, a 220pF ceramic capacitor (marked 220K or 221).
56G. Install C7, a .001uF ceramic capacitor (marked .001 or 102).
57G. Install C11, a 10uF electrolytic capacitor. Check polarity!!!
58G. Install D10, the BB609 varactor diode (black diode with a green
band). The PC board silkscreen for this part looks like a transistor so you’ll
need to be careful to get the orientation right when installing this varactor
diode. The banded cathode end should be placed in the hole closest to
C13. Adjusting the voltage across this diode allows the PLL to do its job.
When in use, this diode is reverse biased so it actually acts as a capacitor.
When the voltage across the diode is high, the depletion layer internal to
the diode gets wider. This causes the capacitance to lower so that the os-
cillator changes frequency.
59G. Install Q2, one of the 2SC2498 UHF transistors. Make darn sure the
flat side is oriented as shown in the parts layout diagram. Notice because
these are not a standard transistor, the pin-out is not C-B-E like with
2N3904 transistors, instead it is B-E-C (Base Emitter Collector).
60G. Install Q1, the other 2SC2498 UHF transistor. Again make sure the
flat side is in the correct direction.
61G. Install VR1, the 78L02 2.5 volt regulator. Be sure the flat side is in the
right direction before soldering. This regulator only powers the BA1404.
62G. Install L1, the shielded metal canned coil. Solder both the mounting
lugs and the two connections. Be careful that you don’t bend over one of
the connections before it goes through the board, these are a pain in the
neck to desolder.
63G. Install Y1, the 6.00MHz crystal (Silver metal can marked 6.00). Make
sure and mount this part flush to the board.
Whew! That was a lot of steps. Definitely check all of your work up to this point
for mistakes in orientation. Double check all of your electrolytic capacitors to be
sure the positive symbols are on the opposite side of the negative stripe. Also
make sure there are no solder bridges or cold solder joints.
If there are no problems up to this point it is time to move on! Now we are on to
easier stuff with less steps. But still be careful of your assembly, you wouldn’t
want to get this far and then make a mistake causing the project not to work.
With soldering iron in hand, on to the next section!
Содержание FM-100
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Страница 22: ...FM 100 Page 22 MAIN BOARD PART LAYOUT...