SBC-3 Construction

SBC-3 contains through hole parts and a few surface mounted parts.   With care, the average hobbyist can successfully build this project.

The board measures 4" x 6.5" - Here is a parts reference:

The following are most of the parts needed to build SBC-3.

Part ID   Description       Digikey Part #
=============================================
C1        220uF             493-1492-ND
C2        0.1uF             BC1160CT-ND
C3        0.1uF             BC1160CT-ND
C4        0.1uF             BC1160CT-ND
C5        220uF             493-1492-ND
C6        220uF             493-1492-ND
C7        0.1uF             BC1160CT-ND
C8        1uF               P13460-ND          ALT 493-1099-ND
C9        1uF               P13460-ND          ALT 493-1099-ND
C10       1uF               P13460-ND          ALT 493-1099-ND
C11       1uF               P13460-ND          ALT 493-1099-ND
C12       1uF               P13460-ND          ALT 493-1099-ND
C13       .01uF             BC1158CT-ND
C14       .01uF             BC1158CT-ND
C15       .01uF             BC1158CT-ND
C16       .01uF             BC1158CT-ND
C17       .01uF             BC1158CT-ND
C18       .01uF             BC1158CT-ND
C19       .01uF             BC1158CT-ND
C20       .01uF             BC1158CT-ND
C21       .01uF             BC1158CT-ND
C22       .01uF             BC1158CT-ND
C23       .01uF             BC1158CT-ND
C24       .01uF             BC1158CT-ND
C25       .01uF             BC1158CT-ND
C26       .01uF             BC1158CT-ND
C27       .01uF             BC1158CT-ND
C28       .01uF             BC1158CT-ND
C29       .01uF             BC1158CT-ND
C30       10-30pf           490-3703-ND  (20pf) (PAL ONLY)
F1        1A                507-1013-ND
F2        375mA             507-1010-ND
F3        375mA             507-1010-ND
F4        375mA             507-1010-ND
F5        100mA             507-1004-ND
IC1       W65C816S          WDC - W65C816S6PG-14 
IC2       CY7C1049B         428-1980-5-ND
IC3       28256             CAT28C256LI-12-ND
IC4       XC95108           122-1460-ND
IC5       AD724             Newark.com - 87H9975
IC6       DS1813            DS1813-5+CT-ND
IC7       LM7805            497-1443-5-ND
IC8       XC9572            122-1443-ND
IC9       W65C22            WDC - W65C22S6TPG-14
IC10      W65C22            WDC - W65C22S6TPG-14
IC11      ATMega8           ATMEGA8-16PU-ND
IC12      MAX232            296-1402-5-ND      Alt MAX232CPE+-ND
J1        Power jack        CP-102A-ND
J2        Comp Vid Out      CP-1403-ND
J4        VIA1-A            *  A26529-40-ND
J5        VIA1-B            *  A26529-40-ND
J6        VIA2-A            *  A26529-40-ND
J7        VIA2-B            *  A26529-40-ND
J8        SPI Expansion     *  A26529-40-ND
J9        6 pin DIN sckt    CP-4060-ND
J10       SPI 0             *  A26529-40-ND
J11       SPI 1             *  A26529-40-ND
J12       SPI 2             *  A26529-40-ND
J13       SPI 3             *  A26529-40-ND
J14       SPI 4             *  A26529-40-ND
J15       SPI 5             *  A26529-40-ND
J16       Serial Port       A35105-ND          Alt A32072-ND
J17       SPI 7 or EXTC     *  A26529-40-ND
JP1       DTR-DSR           #  SAM1029-06-ND
JP2       CTS-RTS           #  SAM1029-06-ND
JP3       J5-CB1VIA1-ATM8   #  SAM1029-06-ND
JP4       J5-CA1VIA1-ATM8   #  SAM1029-06-ND
JP5       AD724 NTSC Clk    use wire
JP6        NTSC/PAL         #  SAM1029-06-ND
OSC-1     14.318 MHz NTSC   XC246-ND (NTSC ONLY)
OSC-1     16 MHz PAL        X216-ND  (PAL ONLY)
R1        75                75QBK-ND
R2        75                75QBK-ND
R3        75                75QBK-ND
R4        1.8k              1.8KQBK-ND
R5        1k                1.0KQBK-ND
R6        470               470QBK-ND
R7        1.8k              1.8KQBK-ND
R8        1.0k              1.0KQBK-ND
R9        470               470QBK-ND
R10       680               680QBK-ND
R11       330               330QBK-ND
R12       75                75QBK-ND
R13       10k               10KQBK-ND
R14       10k               10KQBK-ND
SW1       Power switch      432-1168-ND
SW2       RESET             CKN1667-ND         Alt P8072SCT-ND
XTAL1     4.43 MHz          X083-ND (PAL ONLY)
          Heat Sink plcc84  345-1060-ND
          Heat Sink tO-220  345-1016-ND
          9v power pack     % T460-P5P-ND
          plcc44 socket     ED90008-ND
          plcc84 socket     ED90011-ND
          dip28 .6 socket   ED3728-ND
          dip28 .3 socket   ED90054-ND
          dip 40 socket     ED3740-ND
          dip 16 socket     ED3316-ND

*  A26529-40-ND is a 2x40 pin breakable header 		
Buying 2 will be enough for all parts		

#  SAM1029-06-ND is a 1x6 pin breakable header
Buying 2 will be enough for all parts
   SAM1029-50-ND IS A 1X50 pin breakable header - buy just 1

%  If you don't want to buy the wall wart, you can buy the plugs for the power jack and make your own.
Digikey part # is CP3-1000-ND

Detailed steps for construction

1) Install the 36-pin SOJ SRAM Chip. This will be the harded conponent to install. See my comments below for help in sucessfully installing this part. I used an ohm meter to test that each pin was soldered correctly and that adjacent pins were not shorted. Use the schematic and PCB trace pictures to help

2) Install the AD724. This should go much easier than the first part.

The rest of the parts are through-hole and should be simple.

3) You can see if your C18 & C19 will fit on top of board and under the 84 pin PLCC socket. If so, install the caps then the socket. If not, you can solder the caps on the bottom of the board. I drilled holes in the socket above the caps to allow for top of board installation.

4) Install chip sockets for all of the IC's - at least the programmable ones so they can be removed if reprogramming becomes necessary. Do not install any chips yet. Ensire PLCC sockets are oriented with PIN 1!

5) Install all of the resistors - be sure to get the right value for each.

6) Install the jumper blocks and I/O blocks. Break the parts to the correct size using an exacto knive or utility knife.

7) Install the bypass capacitors. C18 and C19 were installed in step 3. Keep the leads short.

8) Install the fuses. You can use wire if you don't want to install the fuse. The fuses are larger than I expected so mount them veritcally (bend one end around so its beside and parallel with the other.

9) Build the power supply by installing the following parts: J1, SW1, C5, IC7 (7805), C6 and C7. Leave the leads of IC7 long and solder it at the ends, so it stands high on the board. This will give more room for the heatsink to clear the C5 & C6.

10) Apply +9 VDC power to J1 and turn on SW1 (handle towards IC7). Check for +9v and +5v on the IC power pins (refer to datasheets) and I/O ports. Check IC2 and IC5 to ensure they are not overheating from a shorted solder connection.

If all checks good, then proceed. If not, troubleshoot and correct first.

11) Install J2, J9, J16, C8 - C12, C1.

12) For NTSC, install the 14.318MHz Oscillator (use a socket if desired) and the jumper from JP5 to the lower pad of C30 (C30 and XTAL1 are not used).
For PAL, install the 16MHz Oscillator, 4.43MHz Crystal, and C30 (you may want to test it before soldering C30). C30 may be 10pf to 30pf in value.

13) Install a shorting block on JP6 - pins 1-2 for NTSC and 2-3 for PAL.

14) Install IC6 (DS1813) and insert IC4 (XC95108) into its socket, noting the location of PIN 1. You can leave the heatsink off for now to help remove the IC if needed.


*** Power should only be applied for 2-3 minutes at a time. If more time is needed to troubleshoot, Give the XC95108 time to cool in-between or place the heatsink on top (use a rubberband to hold it in place). Ensure IC7 (7805) has a heatsink installed.


15) Connect a video cable to J2 and to your monitor. Turn on power. You should see a random but stable pixel pattern on the screen.
If so, then proceed. If not, troubleshoot by using a logic probe or scope to ensure the RAM addresses are cycling and the CSYNC is being generated. The XC95108 is reading the RAM (random pattern of 1's and 0's) and generating the CSYNC.

16) Power off and install the EEPROM and CPU into the sockets. Re apply power and check the display for an SBC-3 splash screen. If its there, great, proceed. If not, check the reset line to the CPU and ensure the power supply is still working properly.

17) Install the remaining IC's, watching pin 1 orientation. IC8 (XC9572) is mounted with pin 1 pointing down.

18) Install shorting block in pins 2-3 of JP3, and pins 1-2 of JP4. JP1 and JP2 provide shorts on RS-232 handshake lines DSR-DTR and RTS-CTS respectively. They are optional.

19) Install a keyboard in J9 (PS/2) and re-apply power. You should see all three LED's come on then go out. The Numlock will come back on. Try typing something, the monitor should have provided a ">" prompt and your keystrokes should be displayed.

20) At this point, if all works good, install the heatsink to IC4 (XC95108). You can keep power on without restriction from this point on.

You can connect a null-modem cable from your PC to the SCB-3 J16 (RS-232) and try to do an xmodem transfer.

If you encounter trouble along the way, verify connections and pin orientations and check for valid and expected signals.

You can email me with questions and I'll try to help you past any stumbling point.

Finally, go play!!!


The follow narative describes my experiences with SMT soldering while building the SBC-3 core.

First, let's define some things.

Flux - This is used to help the solder flow and bond easier.   It is already in the core of most solder rolls.   However, itís not enough for SMT work.   Flux also comes as a stand alone product, in paste and liquid form.   Adding flux to the PCB is necessary in SMT work to help the minimal amounts of solder do its job.

Solder paste - This is a solder and flux mixture in a paste form.   I read that solder with a small silver content will melt at a lower temperature than standard tin/lead solder.   The paste I bought had silver in it but it also had a fibrous type consistency that proved troublesome.   I'll explain later.

Solder Mask - This is the (usually) green coating over the PBC's traces everywhere except where your components mount.   Its job is to help solder from getting where you don't want it.   It also helps reduce solder bridges.   This is very helpful in SMT work, but I've read itís not mandatory if you are careful.

The 4 packages I've used so far are a 36 pin SOJ, 16 pin SOIC, 32 pin QFN, and a 1206 resistor.   See the references below for the datasheets - they have package drawings included with them.   The 1206 resistor was done on some VHF radios at work.   We had to remove a 0 ohm part and replace it with a 1.5k Ohm part.   That went well.   You don't need to add much solder at all to get those to bond.

The 36 pin SOJ was my first IC.   The SOJ pins curl under the IC, which makes soldering a little difficult.   I started with an ExpressPCB miniboard.   These boards have a tin coating over the copper traces but no solder mask.   I read that most boards have enough solder content in this coating to attach your parts directly without adding solder.   Attempt 1 failed badly.   They recommend tacking down opposite corners first.   I did that.   Then you should work your way around the chip heating all pins.   This resulted in about 40% of the pins actually bonding to the board.   So, I tried adding solder.   This turned into a huge mess.   My soldering iron tip was too big.   Some traces separated from the pad due to overheating and I had some solder bridges to clean up.   The end result was 33 completed connections with 3 bridges that extended under the IC.   Scrap that one!

Attempt two was another 36 PIN SOJ with a new miniboard.   This time I used a new iron with a smaller tip and added solder paste to the board before placing the IC.   The paste had a fibrous content that made it hard to keep paste on just the pads.   I ended up spreading it down each row of pads.   The idea was the flux would help draw the solder to the pads.   I placed the IC then tacked two corners.   I proceeded to heat each pad and saw that the extra flux did help draw the solder to the pads.   I ended up with a 34 pins properly connected.   The last two required just a little more heat.   The down side was that there was still some un-melted solder paste between some of the pads.   That fibrous content caused some bridging that I didn't detect until I put the part through a test procedure and the O'Scope found them.   I used a single strand from stranded wire I had (approx size of our #30 wire wrap wire) to scrape the excess paste from between the pads.   At this point I was at work and used a magnifying lamp to help.   The pins are on 0.05 inch centers (half the spacing of the 0.1 inch DIP pins) and magnifying lamp was extremely helpful.   The part ended up working fine after that bit of cleaning.

The next part was the 16 pin SOIC.   I added solder paste to the pads and placed the part.   Tacked two corners and heated each pin.   This part was much easier as the pins are exposed.   I completed it in two minutes without trouble.   I did clean up the pads afterwards to remove excess paste.   It ran good the first time.

The last part was the 32 pin QFN.   It is extremely small - 5mm square.   The pad spacing is on 1/2 millimeter centers!   The Schmartboard really saved me here.   They are designed with a thick solder mask that creates valleys for the pins to fall into.   This helped with alignment and soldering.   Also, there is enough solder already on the traces to do the job.   You just add flux and heat the traces, moving your iron towards the pins to push the solder.   Read more about it on the Schmartboard website.   You need a very fine-tipped iron to use these boards.   It took me several re-tries to get all 32 pins bonded but I did it without adding solder.   I would try to run the part and it would not respond, so I reheated the pads.   I got to where I could talk to it over the address and data pins, but the tx and rx still didn't work right.   More reheating finally yielded a working UART.   I'm not sure if I want to try that part on a miniboard.   I may have to add a solder mask to my finished SBC-3 board in order to use it, or use a larger part from the same family.

So, what have I learned?   Use solder sparingly and flux generously.   Be patient and use a magnifying lamp to save your eyes.   A good iron (does not have to be expensive) with a fine tip is mandatory!   Keep the tip clean!   I used an ohm meter after soldering to verify that each pin was bonded to the pad - I did that by touching the top of the pin (not the pad) with one lead, and touching a connected pad or trace with the other lead.   The QFN package will not allow this method, but the SOIC and SOJ does.   For QFN parts, I found a logic probe worked well.   A good pair of tweezers is also recommended.   Although I have not used them yet, I agree, a good pair would be very helpful.

Would I recommend this to others?   Yes.   But I recommend reading up on these techniques and watching as many YouTube videos as you can find.   Filter out what will work for you and what won't.   Be prepared for failures and ruined parts and boards at first.   If you are able, pull some scrap PLCC parts from sockets and practice on cheap pre-made boards.

Resources:

CY7C1049B 36 pin SOJ
AD724 16 pin SOIC
XR16L580 32 pin QFN
32 pin QFN Schmartboard
Schmartboard instructions
My Soldering Iron
Extra small iron tip
My Solder paste
My Flux
My Logic Probe
YouTube videos
IC package types nfo


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All info provided "as-is" and is Copyright 2008.
Last updated on Sep 5, 2008.