Issue 5, April 1994
Mic-PreEminence User Guide
Page 18
Studio Technologies, Inc.
4)
Carefully remove the selected capaci-
tors. Use correct desoldering technique
for double sided boards. Do not use
force as that will ruin the plated-through
holes.
5)
Install and solder the replacement
capacitors into the board.
6)
Return the top and bottom cover to
their correct location and put the screws
back in.
7)
Check the Mic-PreEminence for correct
operation.
Appendix D
Solutions for RF Problems
The Mic-PreEminence’s circuit board
contains four locations (two per channel)
where chokes (inductors) may be installed.
These chokes, along with existing Mic-Pre-
Eminence circuitry, create low pass filters.
From the factory 51 ohm resistors are
inserted in locations R6 and R7 for channel
1, and R11 and R12 for channel 2. If RF
problems occur chokes should be installed
in series with these resistors. The first thing
to do is to obtain four 100uH chokes. A
good source to obtain these parts is Digi-
Key Corporation, P.O. Box 677, Thief River
Falls, MN 56701 U.S.A., telephone U.S.A
1-800-344-4539. They are well-equipped to
handle small orders and have a wonderful
catalog. The recommended part is the
8230-68 (Digi-Key part number M8037) or
9230-68 (Digi-Key M9101) made by J.W.
Miller division of Bell Industries. These
devices are about the size of ¼-watt resis-
tors; they are very easy to handle and
install.
The following procedures must be
performed by a qualified technician.
Operating the Mic-PreEminence with
the top and/or bottom cover removed ex-
poses the technician to points in the power
input section with hazardous voltages.
1)
Ensure that the AC mains cord is re-
moved from the Mic-PreEminence AC
mains input connector on the back panel.
2)
Remove the top and bottom cover (four
Phillips head screws for each cover).
3)
You will be installing four chokes in
series with four resistors. They should
be installed to form what circuit board
assembly people refer to as a “teepee”
arrangement. Using a soldering iron,
carefully lift one end of resistors R6, R7,
R11, and R12 (51 ohms) from their
solder pads. Use a solder “sucker” or
“solder wick” to open the holes in solder
pads. Don’t hurt the printed circuit board
with excessive force or heat.
4)
Insert and solder one end of a 100uH
choke into one of the empty solder pads.
Cut the excess choke lead on the under-
side of the circuit board. Solder the other
choke lead to the free end of the 51 ohm
resistor that was removed from the
solder pad. Cut the excess choke lead
from the newly formed junction of the
choke and the 51 ohm resistor. The two
components should neatly stick up from
the circuit board, forming an inverted “V”
or the “teepee.” Repeat this procedure
for the other three chokes.
5)
Return the top and bottom cover to
their correct location and put the
screws back in.
