Tucson T-238 Assembly Manual Download Page 7

 

T-238 Assembly Manual 

Rev. 1 February 2001 

Page 7 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 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. 
 
Before applying power for the first time, please check the 
following: 
 
[  ] ICs U3 and U4 are NOT installed. 
 
[  ] Check that oscillators U1 and U2 are oriented correctly.  
Three of the corners are rounded and one is squared.  The 
squared corner is pin 1 and should match the square pad 
on the printed circuit board. 
 
[  ] Check the polarity of all the electrolytic or tantalum 
capacitors.  The capacitors negative 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 diodes D1, D2, and D3.  The band 
on the diode should match the extra stripe  on the PCB 
silkscreen. 
 
[  ] Headers J6, J8 and J10 are not connected. 
 
[  ] The LCD should not be plugged in. 
 
[  ] Jumpers OJ1 and OJ2 have jumper between pins 1 and 
2. 
 
The T238 kit does not come with a power supply.  An 
ordinary wall transformer (“wall wart”) that provides 9 to 12 
Volts DC at 300 milliamps will work fine.  The T238 is fitted 
with a 2.1mm power coaxial connector such that the center 
conductor is positive and the outer barrel is ground.  
Measure this with a voltmeter to confirm both the voltage, 
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 voltage is between 9 and 12 Volts DC and the 
center conductor is positive and the barrel is ground 
 
[  ] 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 2 of U3.  
This will be the ground reference for the rest of the 
measurements.   
 
[  ] Measure the voltage on the voltage regulator U5 on the 
pin furthest from the power jack.  It should be between 8 

and 14V.  If it is 0V, then L1 is likely missing or damaged.  
If it is low,  the transformer may not be rated for the right 
voltage or something may be overloading it.   
 
[  ] Measure the voltage on the voltage regulator U5 on the 
pin closest to the power jack.  It should be between 4.90V 
and 5.10V.  If it is low, something could be overloading the 
regulator and whatever is doing that should be hot.   
 

WARNING! – 

Don't proceed until the voltages in and out of 

the voltage regulator U5 are within proper limits. 
 
[  ] Voltages in and out of voltage regulator U5 are within 
limits. 
 

NOTE  – 

In the sections below, there are frequent 

references to +5V, which actually means the voltage 
between 4.90V and 5.10V that you measured above. 
 
With the ground lead of your voltmeter still on U3 pin 2, 
confirm all the following test points also measure  +5V.  
Remedies are listed if you do not see +5V. 
 

Check 

Pin 

Remedy if not +5V 

[  ] 

U4 pin 16 

Check socket. 

[  ] 

J2 pin 2 

Check socket and L8 

[  ] 

J2 pin 3 

Check socket, L2, and R11 

[  ] 

U3 pins 1, 20, 
and 31 

SW5 possibly installed 
backwards.  Check by 
pressing SW5.  If voltage 
appears when the switch is 
pressed, it is in backwards. 

[  ] 

U3 pin 14 

Check OJ2 

 
Next check the four switches following the table below.  For 
each pin on the microcontroller, verify that the voltage is 
normally 5V.  Pressing the switch makes the voltage go to 
0V.  If the voltage is always low (regardless of the switch), 
then likely the resistor is not installed correctly.  If the 
operation is opposite (normally low and pressing the button 
makes the voltage go high), then the switch has been 
installed backwards. 
 

Check 

U3 Pin number 

Switch 

Resistor 

[  ] 

U3-26 

SW4 

R10 

[  ] 

U3-27 

SW3 

R9 

[  ] 

U3-28 

SW2 

R8 

[  ] 

U3-29 

SW1 

R7 

 
Using a small wire bent in a U-shape, short between U3 
pins 20 and 21.  Do this carefully so you don’t damage the 
IC socket.  The LED should light.  If it does not, there is a 
problem with R12 or more likely, the LED is installed 
backwards. 
 
[  ] LED works 
 
[  ] Remove power from the T238. 
 

Summary of Contents for T-238

Page 1: ...tended for use with the Dallas Semiconductor 1 Wire bus and any device that needs a serial connection Four push button switches and a Liquid Crystal Display LCD provide the user interface The initial application for the T 238 is a controller that accepts data from a Dallas Semiconductor weather sensor unit processes it and formats it for sending either directly to a Terminal Node Controller TNC fo...

Page 2: ...tor 1 2 w 5 Carbon Film 1 4 7 Ω yellow violet gold R13 Resistor Trimpot 1 10K Ω Trimpot 103 V1 Capacitors Capacitors may be marked in various ways The typical markings are listed but may vary Find all that match and the remaining ones if any should become apparent by elimination Mylar or Monolithic 5 0 1 uf 104 C3 C7 Electrolytic or Tantalum 5 1uF 105 or 1 35 C8 C12 2 10 uf C1 C2 Diodes 2 1N4148 S...

Page 3: ...ayout diagram for clarification of parts placement All references to up down left and right assume that you are looking at the PCB with the text right side up that is the four switches are at the bottom and the five big connectors are at the top Resistors Resistors have a lead spacing of 0 4 and should lie flat on the PC board You may wish to use a lead former to pre form the resistor leads for ne...

Page 4: ...oldered connections or cold gray and or grainy looking solder connections OK so far This completes the IC socket installation Capacitors All capacitors should be mounted as nearly flush to the board surface as practical without stressing the leads Install the following capacitors C3 0 1 uF 104 C4 0 1 uF 104 C5 0 1 uF 104 C6 0 1 uF 104 C7 0 1 uF 104 Solder and clip the leads 10 total Electrolytic a...

Page 5: ...arked on the PCB with a square pad Pin 1 on the crystal oscillator is marked with a black dot and or an edge of the can that is square instead of rounded CAUTION Make certain that the U1 metal housing does not short to nearby R10 or R12 U1 32 000 MHz U2 9 8304 MHz Solder and clip the leads 8 total Connectors Gently rock the RJ 11 connector until it snaps into place and solder the leads J2 RJ 11 co...

Page 6: ...x16 pin male header with pins facing to the rear of the LCD module and in holes 1 through 16 NOTE J8 on the PCB is an alternate connection for powering the LED backlight on the LCD There will be a red and black wire a polarized Molex plug housing and two pins remaining These are for LCD displays that do not have a 16 pin header but rather a 14 pin header Pins 15 and 16 supply power to the LED back...

Page 7: ...as components heating up smoke or smell Remove power immediately if anything unusual appears Place the ground lead of your voltmeter on pin 2 of U3 This will be the ground reference for the rest of the measurements Measure the voltage on the voltage regulator U5 on the pin furthest from the power jack It should be between 8 and 14V If it is 0V then L1 is likely missing or damaged If it is low the ...

Page 8: ...t 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 rib...

Page 9: ... not cause any damage but the unit will not work Some telephone cables reverse the wires and some do not In addition some telephone cord couplers reverse the wires Find a telephone cable that does not reverse the wiring Hold the connectors side by side and oriented the same direction for example the clip tab down on both connectors Observing the red and green wires inside If for example red is on ...

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