T-238+ Assembly Manual Rev. 8 March 2006 Page 5 of 6
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 voltages 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.
NOTE: -Before you power up the modem board, your
T238+ main board should be constructed and fully
checked out.
Pre-Power Check
Before applying power for the first time, please check the
following:
[ ] ICs U100 and U101 are NOT installed.
[ ] Check the polarity of all the electrolytic or tantalum
capacitors. The capacitorsnegative side is usually
identified with a white stripe and a big minus sign on it.
The positive side is identified on the PCB. Not all the
capacitors have the same orientation; double-check them
with reference to PCB silkscreen.
[ ] Check the polarity of the transistor, does the flat side
on the part match the silkscreen on the board?
[ ] Headers P100 and P101 are not connected.
[ ] Header P102 is installed on the BOTTOM of the board.
[ ] Plug the modem into the T238+. Take care to make
sure there are no components from the T238+ touching
the bottom of the board. Use the screws and spacers to
ensure a good fit for the board.
[ ] Apply power to the T238+. Observe anything unusual
such as components heating up, smoke or smell.
Remove power immediately if anything unusual appears.
Place the ground lead of your voltmeter on pin 4 of U101.
This will be the ground reference for the rest of the
measurements.
NOTE –In the sections below, there are frequent
references to +5V, which actually means the voltage
between 4.90V and 5.10V.
With the ground lead of your voltmeter still on U101 pin 4,
confirm all the following test points also measure +5V.
Remedies are listed if you do not see +5V.
Check Pin Remedy if not +5V
[ ] U100 pin 16 Check socket.
[ ] U101 pin 8 Check socket.
[ ] P100 pin 9 Check connector
[ ] P100 pin 6 R109, D101, Q100.
[ ] Check the positive pin of C108. It should be between
2.45 and 2.55V. If not, check R114, R115, C108
(polarity), C109, R112, R113.
Using a small wire bent in a U-shape, short between U100
pins 14 and 16. Do this carefully so you don’t damage the
IC socket. The amber “BUSY” LED should light. If it does
not, there is a problem with R106 or more likely, the LED
is installed backwards.
[ ] Amber LED works
Using a small wire bent in a U-shape, short between U100
pins 3 and 16. Do this carefully so you don’t damage the
IC socket. The red “XMIT” LED should light. If it does
not, there is a problem with R111, R109, Q100, or the LED
is installed backwards.
[ ] Red LED works
[ ] Remove power from the T238+.
Next you will insert U100 and U101. Make sure you
match the pin-1 notch of the device to the notch on the
silkscreen. It can be difficult to line the pins up with the
socket. Your best bet is to place the chip sideways on a
flat static-safe surface so that one row of the pins all lie
flat on the surface. Carefully rotate the body of the IC
while pushing down on the pins. Rotating while pushing
down should bend all the pins together and bend them
where they protrude from the body. Bend the pins a little
at a time, then check to see if they are perpendicular to
the body of the IC. Once perpendicular, the pins of the IC
will be much easier to insert as they line up with the
socket.
Insert U100 and U101 slowly. Observe that all the pins
slide into the socket. Watch for pins that bend under the
IC or out of the IC socket.
[ ] Insert U100, MX-614.
[ ] Insert U101, LM358.
[ ] The notch on the chip is aligned with the silkscreen
notch on the PCB.
[ ] Apply power to the T238+. The red LED on the main
board or button board should still flash three times quickly,
and after approximately 10 seconds it should start flashing
once per second.
If the LED does not flash at all, remove the modem board
to confirm the LED works OK without the modem board
installed. If it does, check the modem board for short
circuits, especially between the connector and MX-614.
