Check Fix on the PCB
It is so hard to make the perfect board; this one is no exception. Line "G" on the PIC board was extended so it shorted the 220 ohm resistor taking it out of the circuit.
Two problems resulted, a very bright "G" segment and it blew out the 4077 IC chip.
The fix is to cut the "G" segment line just above the bottom connection to the 220 resistor. This fix will be done before the boards are shipped, but it is a good idea to double check this fix before stuffing the board.
With a DVM on ohms, check for no connection between the "G" line resistor pads.
Arrows show where the leads of the DVM go to check fix.
Picture showing the fix on the bottom side of the board and pads to place the DVM leads to check the fix.
If you do get a connection between the two points, use a sharp knife, razor blade, or some appropriate instrument to make sure there is no connection between the pads of the 220 ohm resistor.
The location of the cut is important. The hole in the upper right of the small copper square of the fix must remained connected to the upper lead of the 220 resistor. If you get a board without the cut, make the cut in the same place as shown in the above picture.
Step 1 - Resistors
The footprints for the resistors have the value printed inside the footprint. Double check the value when inserting a resistor. Bend the leads of the 1/8 watt resistors about 1/16" from the body of the resistor to fit into the footprint. The leads of the 1/4 watt resistors are bent right against the body of the resistor.
1 - 10K, 1/8 watt, bend leads 1/16" from body
3 - 1K, 1/8 watt, bend leads 1/16" from body
4 - 100K, 1/8 watt, bend leads 1/16" from body
2 - 6.8K, 1/4 watt, gently bend leads against body
8 - 220 ohm, 1/4 watt, gently bend leads against body
Step 2 - Diodes
4 - 1N4148 diodes, bend leads 1/16" from body
Make sure the black band on the diode is inserted the correct way. The wide white band on the footprint is where the black band should go on the diode. To double check, the bands should be opposite each other at each pair.
Step 3 - Capacitors
1 - .1
1 - 2.2mfd electrolytic
1 - 100mfd electrolytic
Notice the electrolytics are polarized, they must be put in with the ground and positive side correctly. The short lead on the electrolytics is ground and the long lead is positive. The plus "+" side is marked on the board. Put them in incorrectly and they could explode or get very hot!
8 - .01, Note: Some kits may contain large .01 disc capacitors.
Start on the left side of the board and work around the top edge to the left side to get them all.
2 - .01 bottom side of board - Do not solder now!
This picture shows the location on the top of the board where two .01s are soldered underneath the board.
These will be put on the board in Step 8 after the ICs and 10 MHz oscillator have been soldered on the board.
Step 4 - 2N3906 Transistors
The kits have 7 - 2N3904s with straight leads for the LED cathode drivers and one flared (on a small piece of cardboard) for the crystal oscillator switch.
It is not necessary to push the transistors against the PCB. The footprint for the transistors was necessary because of the tight fit between the traces for the LED readout. As a result, a slight offset of the center lead is needed to fit the transistors in the footprint.
7 - 2N3906 straight leads
Insert 3 2N3906 in the top row. Notice the flat side of the transistor and match it to the footprint flat.
Solder the lower row of pins first. Then clip those leads so there is better access to the top row of leads. Solder the remaining leads.
Insert 4 2N3904 in the lower row. Match the flat of the transistor to the flat of the footprint.
Solder the lower row of pins first. Then clip those leads so there is better access to the top row of leads. Solder the remaining leads.
Check for solder bridges and bent wires shorting against adjacent pins after soldering and clipping all the transistor leads. Solder bridges can be easily removed by wiping the tip of the soldering gun between the pins.
1 - 2N3906 flared leads
Cut the transistor from the cardboard and insert in the place indicated above by the yellow arrow.
Step 5 - 7805 and 10MHz Oscillator
Location of parts. Please note the dots in the lower left hand corner of the 10MHz oscillator and the front and heatsink of the 7805 voltage regulator.
Be careful when inserting these parts, they must have correct orientation!
The 10 MHz oscillator can must have the dot in one corner at the lower left hand side as shown above in the picture. The dot is in the footprint and just outside so you can double check after the part is in place.
The 7805 voltage regulator must have the front of the part toward the outside of the board. Also, the front side of the part should be pointed to the part number "7805". The metal heat sink for the 7805 is the back of the part and should be toward the center of the board. See picture above.
Step 6 - PIC IC socket 28 pin
The orientation of this socket is important! Notice the notch on the right hand side of the socket.
The notch on the footprint and the notch on the socket should be seen together as shown in the picture.
Solder all the pins as shown in the picture. The arrows point to the beginning and end of both rows.
The one on the bottom left can easily be overlooked as there are other holes very close by.
Step 7 - Solder 5 ICs
The 5 ICs are soldered in this step. The most important part of this step is getting the notches correctly placed as shown on the footprints on the board.
There are 2 ICs that require special attention.
The first one is the 74AC151:
Pin 5 on the 74AC151 is cut off. Pull the pin out from the IC as shown above and cut it off. Pay particular attention to the location of the notch on the IC.
The picture above shows the location of the IC and the location where the pin is cut for. After the pin is cut insert into the board and solder.
The second one is the 4077:
It was a surprise to see this dot on the part at the wrong location! Insert this part according to the notch only! Ignore the dot.
Next, insert and solder the 2 74HC4046 and the 4066:
Be sure you have it right BEFORE you solder. Removing parts from plated through holes is very difficult.
Step 8 - Solder two .01 caps
This picture shows the location on the top of the board where two .01s are soldered underneath the board. At this time they will be covered up by the oscillator and 28 pin socket.
If you received large .01 disc capacitors with your kit, please click here for instructions. Click "Back" on your browser to return here.
The leads of two .01 caps are cut to 1/8". Insert the caps into the pads and solder. May take a little effort. To make it easier, be sure the width of the leads match the holes before cutting them short.
The Crystal Oscillator sets 1/8" above the PCB, enough to see if the leads of the cap are not touching the bottom of the oscillator. Double check to make sure the leads are clear of the oscillator.
There is little worry with the PIC cap as it is all plastic above where the .01 cap goes.
Step 9 - Solder the 7 LED displays
Look closely at the pin pattern of the readouts and it is obvious that the readouts will fit only one way. The notch is at the top of the readout and the decimal point is at the bottom right side.
The LED displays all soldered.
Step 10 - Solder the Headers on the PIC and Display Boards
The boards are connected back to back. The connecting pads are labeled 1 - 16 on both boards. Identical pin numbers are connected together. The back-to-back configuration gives easy access to the connections on the PIC board.
The headers can be soldered anyway you like. The following is my suggestion. The stronger headers are soldered on the PIC board in case a different display is used later on.
The male headers are soldered on the PIC board. The male headers have short pins on one side and much longer pins on the other. Solder the short pins onto the PCB, they fit perfectly.
Solder one pin of the header and then double check to make sure it is mounted 90 degrees to the board. Reheat the soldered pin if an alignment is necessary.
After alignment, solder the rest of the pins.
The female headers are soldered on the display.
Solder one pin of the header and then double check to make sure it is mounted 90 degrees to the board. Reheat the soldered pin if an alignment is necessary.
After alignment, solder the rest of the pins.
Step 11 - Insert the PIC16F72 into the Socket
Remember to bend the pins toward the center of the IC until they are pointing straight down. Look down the rows of pins to make sure one is not bent further toward the center than the others. If one is bent too far, it may bend against itself or against the bottom of the IC, not going into the socket correctly. This will cause an intermittent error when the counter is turned on.
Lay one side of the pins into the socket, do not push down.
Roll the other side of pins into the socket. They may not fit in. If they don't, push on the pins slightly with your finger until they slip into the socket. Or, bend them some more toward the center of the IC and try again. Be careful, go slowly.
Now push down on the IC to set into the socket. Look down each row of pins to make sure, as best as can be seen, that all the pins are inserted into the socket.
On the machine pin sockets, as shown in the PIC socket solder Step 6, a lot of pressure is needed to seat the PIC. Be sure the pins are all partially seated before pushing the PIC into the socket. If you are h | 
