T-238+ Assembly Manual
Rev. 3 March 2006
Page 9 of 11
Power Up And Initial Testing:
In this section you will slowly power-up the board and
check for assembly errors. It is important that you follow
these steps carefully. You will systematically apply power
to sections of the board while checking v oltages to find
and eliminate errors. Errors take two forms, the kind that
damage components and the kind that don’t. Neither is
desirable, but the kinds that damage components will
require you to find a replacement part.
Pre-Power Check
Before applying power for the first time, please check the
following:
[ ] ICs U1 and U2 are NOT installed.
[ ] Check the polarity of all the electrolytic or tantalum
capacitors. The capacitors negativ e side is usually
identified with a white stripe and a big minus sign on it.
The positiv e side is identified on the PCB. Not all the
capacitors hav e the same orientation; double-check them
with reference to PCB silkscreen.
[ ] Check the polarity of diodes D1, D2, and D3. The
band on the diode should match the extra stripe on the
PCB silkscreen.
[ ] Headers P1, J1, J2, j3, J4, J5 and J6 are not
connected.
[ ] The LCD module should not be plugged in.
First Power Check
The T238+ kit does not come with a power supply. An
ordinary wall transformer (“wall wart”) that prov ides 7 to 12
Volts DC at 300 milliamps will work fine. The closer you
can get to 7V the cooler the regulator will be. Be warned
that may “12V” wall transformers supply much higher
v oltages ev en under load. The T238+ is fitted with a
2.1mm power coaxial connector such that the center
conductor is positiv e and the outer barrel is ground.
Measure this with a v oltmeter to confirm both the v oltage,
but more importantly, the polarity. The Radio Shack
Model 19-1120/19-1140, supplied with the HTX-202 and
the HTX-404 handheld radios, is suitable for this
application.
[ ] The v oltage is between 9 and 12 Volts DC and the
center conductor is positiv e and the barrel is ground
[ ] Apply power to the T238+. Observ e anything unusual
such as components heating up, smoke or smell.
Remov e power immediately if anything unusual appears.
Place the ground lead of your v oltmeter on the center pin
of U3. This will be the ground reference for the rest of the
measurements.
[ ] Measure the v oltage on the v oltage regulator U3 on the
pin closest to the edge of the board. It should be between
8 and 14V. If it is 0V, then L5 is likely missing or
damaged. If it is low, the transformer may not be rated for
the right v oltage or something may be ov erloading it.
[ ] Measure the output v oltage on the v oltage regulator U5
on the pin furthest from the edge of the board. It should
be between 4.90V and 5.10V. If it is low, something could
be ov erloading the regulator and whatev er is doing that
should be hot.
WARNING! –
Don't proceed until the v oltages in and out
of the v oltage regulator U5 are within proper limits.
[ ] Voltages in and out of v oltage regulator U5 are within
limits.
NOTE –
In the sections below, there are frequent
references to +5V, which actually means the v oltage
between 4.90V and 5.10V that you measured abov e.
With the ground lead of your v oltmeter still on U3 pin 2
(center), confirm all the following test points also measure
+5V. Remedies are listed if you do not see +5V.
Check
Pin
Remedy if not +5V
[ ]
U1 pin 16
Check socket.
[ ]
J5 pin 5
(pin 1 closest to
board edge)
Check socket and L4
[ ]
J5 pin 3
Check socket, L1, and R16
[ ]
U2 pins 1, 20,
and 31
SW1 possibly installed
backwards. Check by
pressing SW1. If v oltage
appears when the switch is
pressed, it is in backwards.
[ ]
U4 Pin 14
(abov e square
pad)
Check socket
Next install the button board cable and the button board.
Conv ention has the brown wire as Pin 1, but as long as
you are consistent on both ends it does not matter. Check
the four switches following the table below. For each pin
on the microcontroller, v erify that the v oltage is normally
5V. Pressing the switch makes the v oltage go to 0V. If
the v oltage is always low (regardless of the switch), then
likely the RPACK is not installed correctly or the switch is
installed 90 degrees off.
Check
U2 Pin number
Switch
[ ]
U2-26
SW1 (up)
[ ]
U2-27
SW2 (down)
[ ]
U2-28
SW3 (select)
[ ]
U2-29
SW4 (menu)
