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6) Fit and solder R1, the preset potentiometer
that sets the LCD contrast.
Be careful not to mix up the presets R1 (100K)
and R5 (4.7K)! The code on R1 is "104".
It is a slightly tight fit but apply pressure
carefully and evenly, and the pins of the
potentiometer will fit into the PCB perfectly.
Adjust this potentiometer to the fully clockwise position initially.
7) Fit and solder R5, the preset potentiometer
that sets the PA bias.
Fit and solder the fixed 4.7K resistor R6.
NOTE: the photograph incorrectly shows R5
as 100K ("104"). It should be 4.7K ("472"). Be
careful not to mix up R1 and R5!
IMPORTANT: Turn the trimmer potentiometer all the way ANTI-clockwise, BEFORE applying
power to the U3S board. Please see section "PA bias set-up" below.
8) Solder wire jumpers as shown in the
photograph and diagram below, depending
on your requirements.
Typical jumper connections are shown in the
photograph circled in yellow, and by red lines
on the parts placement diagram below.
Please read the "Hardware options"
sections below, to decide which jumpers to
fit.
The wire jumpers can be made from offcuts from the other components e.g. capacitor leads. When
installing these wire jumpers, I find it convenient to install them as a small semicircular arch,
perhaps 5mm high off the board, as pictured. This is so that later, if they need to be removed (for
different hardware options configuration), you can easily cut the links using wire cutters. It is easier
than un-soldering them.
The W0-W1 and W2-W3 jumpers hard-wire the LPF into the circuit. Note that when a relay is fitted
at RL0, you do NOT connect these two jumper wires. The relay is part of another kit, the relay-
switched LPF board, that expands the capability of the U3S kit to sequence through up to 6 different
bands.
If R2 is installed, in order to reduce LCD brightness, then connect A1-A2 instead of A0-A1 (see
"hardware options" section below). You may decide to connect A0-A3 to use the software-
implemented brightness control.
You may also install a jumper at the +PA and +5V connections at the bottom of the picture below, in
order to power the power amplifier (PA) with the 5V supply. You should leave out this jumper if you
intend to run the PA at a higher voltage. See more details in the
below.
gHardware options h section
6
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