T-238 Assembly Manual
Rev. 1 February 2001
Page 8 of 11
Next you will insert U3 and U4. Make sure you match the
pin-1 notch of the device to the notch on the silkscreen.
There are a lot of pins on U3 and it can be difficult to line
them 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 U3 slowly. Observe that all the pins slide into the
socket. Watch for pins that bend under the IC or out of the
IC socket. Follow the same process for U4.
[ ] Insert U3, MC68HC908GP32
[ ] Insert U4, MAX232
[ ] The notch on the chip is aligned with the silkscreen
notch on the PCB.
[ ] Apply power to the T238. LED DS2 will flash three
times quickly, and after approximately 10 seconds it should
start flashing once per second.
If LED flashes after approximately 30 seconds and then
flashes once every three seconds, either OJ1 in the wrong
position (jumper between pins 1 and 2) or you have the
crystal oscillators swapped. If the jumper is in the wrong
position, power down the T238 prior to changing jumpers.
If the LED does not flash at all, check OJ2 (jumper
between pins 1 and 2). If the jumper is in the wrong
position, power down the T238 prior to changing jumpers.
If the LED still does not start flashing, make sure that all
the pins in U4 were inserted cleanly into the socket and
check the following components carefully: R1, R2, R3, R4,
R5, and R6. Do not proceed until the LED flashes as
described above.
[ ] LED flashing approximately once per second
With a the ground lead of your voltmeter on pin 15 of U4,
check the following voltages:
Check Pin
Voltage
Remedy
[ ]
U4 Pin 16
+5
Check IC socket
[ ]
U4 Pin 2
Greater than
8V
Check IC socket,
C8, C9, C10, C11
[ ]
U4 Pin 6
Less than
-8V
Check IC socket,
C8, C9, C10, C11
[ ] Remove power from the T238.
[ ] Locate the flat ribbon cable. Notice that one of the
leads nearest one of the edges is a bluish color compared
to the rest. This lead denotes pin 1. You may wish to
place another indication of pin 1 such as a sticker on the
connectors.
WARNING!
–
Polarity of the flat ribbon cable must be
observed. Pin 1 of the LCD display must match pin 1 on
the PCB.
[ ] Plug the flat ribbon cable into J10; line up the bluish
stripe of the cable with pin 1 on the silkscreen. Pin 1 on
the PCB is identified with the square pad and silk screen
square around it. It is the closest to U5, the voltage
regulator.
[ ] Plug the other end of the flat ribbon cable into the LCD.
Line up the cable bluish stripe with pin 1 of the LCD
module.
[ ] The flat ribbon cable should lay flat and not twist or
bend when connecting the PCB to the LCD.
[ ] Cable installed with marked wire next to Pin 1 on T238
and LCD.
Place multi-meter in Ohms mode. Measure the resistance
between U3 pin 2 and pin 1 on the LCD module. The
resistance should be less than 1 ohm. If not, the cable is
either bad or installed backwards.
[ ] Resistance from U3-pin 2 to LCD pin 1 is less than 1
ohm.
[ ] Measure the resistance between U3 pin 1 and pin 2 on
the LCD module. The resistance should be less than 1
ohm. If not, the cable is either bad or installed backwards.
[ ] Resistance from U3-pin 1 to LCD pin 2 is less than 1
ohm.
[ ] Adjust VR1 to mid-position.
[ ] Apply power to the T238.
[ ] After about 1 second you should see the opening
banners displayed on the LCD module. If you do not see
them or they look dim or overly dark, adjust VR1, the LCD
contrast adjustment. Fine tune VR1 for best viewing. If
text is not visible, check the soldering on U3 and J7 as well
as the LCD cable and the header on the LCD module.
[ ] LCD showing legible text.
During the power up sequence, you will get a message
saying that there is a 1-wire bus error. If the error says no
devices are present, you are OK. If it says the bus is
shorted to ground, then check U3, J6, D2, D3, R11, L2,
and J2 for assembly problems or bad solder joints.
Do not select any menu options at this time.
[ ] Received error message saying no devices on the bus.