Building the SX28 based game system (Joystick port version)
|Note: There is a separate assembly instruction for the version with built-in joypad.|
This text describes how to build my SX28 based game system (Joystick port version), before you start you should read through the whole text one time. Note that many components are sensitive to too much heat and will get damaged if you heat them too much when soldering. The drawn placement images show components to mount in each step in black and the components mounted in previous steps in gray.
When soldering the components onto the PCB it is easier if you can put the PCB with the components side flat down, so you should solder components of the same height at the same time. To be able to add components of different height you'll need to start with the lowest first and build your way up.
The first thing to mount when adding components to a single sided PCB is the wire bridges because they are the lowest "components", there are three wire bridges. I'm using 0.5mm tinned copper wire for the bridges as seen in the picture below:
|Location of the seven wire bridges.||Photo of the wire bridges mounted.|
Add the 22 resistors (9 x 221 , 12 x 442, 1 x 10k). Note that the reisistors used for the R2R-DA-ladder (221 and 442) must be 1% or better in order to get a linear output from the DA.
|Location of the 22 resistors.||Photo of the resistors and the diode mounted.|
The next step is to add the three sockets, the 1nF and the two 100nF capacitors (if they are of the same height as the sockets, mine was), the reset switch, the 100ohm potentiometer and the diode recifier bridge. Note that the sockets should be mounted with their polarization as in the component placement image with their dipple marking pin-1 in the same direction as in the image. The rectifying bridge also has polarity, the + and - are usually printed on the capsule in the same way as in the image.
|Location of the sockets, caps, switch, pot and diode bridge.||Photo of the sockets etc. mounted.|
The two 3.3uF capacitors and the SX-key 4 pin angled programming header should be mounted next. The 3.3uF capacitors are polarized and should have their plus side mounted at the side that is marked with a plus in the placement image below:.
|Location of caps and 4p programming header.||Photo of the caps and programming header mounted.|
7805, LED and high pin headers
Now you can mount the 7805 (including cooler), the 3-pin jumper pin header, the 2.1mm power jack and the LED. Note that the LED is polarized and should be mounted with the flat side towards the reset switch. The 2x5pin programming header is mounted with the gap closest to the side of the PCB.
|Location of connectors and last caps||Photo of the caps and connectors mounted.|
Conectors and high capacitors
Now you can mount the remaining components: The two female RCA connectors, the two 9p male DSUB connectors and the two 100uF capacitors. Note that the 100uF capacitors are polarized and should have their minus-side mounted closest to the edge of the board.
|7805 location on PCB||Photo of 7805 mounted.|
Safety tests before turning on the power.
The only thing left on the board then is the microcontroller and oscillator that should be mounted in the sockets later, but before mounting the socket we need to do some tests to prevent it from burning up in case something is wrong. First use a multimeter to measure if there is a short between VDD and GND (pin 1 and 2 of the 28p socket). If so then you have a short between VDD and GND and you should follow the VDD-line on the PCB and check for shorts between the VDD line and the ground plane. After removing all the shortcuts between VDD and GND you can apply 8 volts with a current limit of about 70mA to the power jack. If the current is over 30mA then there is something wrong, check that all components are mounted according to this description and all shortcuts have been removed so the power consumption gets less than 30mA.
Now you can put the microcontroller in the socket. Note the polarization
of the SX should be the same as the socket. Before turning on power again, make sure the
current limit is still on just to be safe. Check the current consumption, at this point the
consumption should be about 55mA. Increase the current limit to about 200mA, then you can mount
the oscillator. When turning on the power the current consumption should be around 145mA, if it
is around 85mA you most likely have a short between the reset-pin-line and ground. Remove reset
shortcuts before you can continue.
Note that there is an empty socket on the board, it is intended for an EEPROM but it is not used by my games so you don't need to add it. On the PCB there is also room for two PS/2 (6p miniDIN) connectors but they are not used by my games (yet).
Now you can connect the TV to the system. Use a prefabricated SCART or RCA cable that connects to the SCART connector or the composite video input on your TV. The right connector is video and the left one is audio. You will be able to control the sound volume using the potentiometer close to the video connector. What channel to select on your TV is depending on your brand and model, consult your TVs manual for which channel to use for the SCART or composite video input connector you connected the system to.
If you don't get an picture at all, make sure the the oscillator jumper is set in the OSC-position, the oscillator output has no shortcuts to ground and that your TV has the correct channel selected. If you have an oscilloscope you can check that the oscillator works and that the video output is generating a video signal.
If you get a black and white picture there can be a sveral reasons, for example:
If you get a colors but the picture is kind of distorted and the colors are not the same as in my homepage then there probably is a short between one or several resistors in the DA and ground, remove the shortcuts and the problem shall be solved.
If the picture is much distorted vertically or horizontally, make sure the video DA resistors connected the video RCA connector has no shortcuts to ground and is correctly connected.
SX Game System (C) Rickard Gunee. This is open source, use this at your own risk ! You may use the information on this page for your own projects as long as you refer to the original author (by name and link to authors homepage), don't do it for profit and don't hurt or harm anyone or anything with it. The author can not be held responsible for any damage caused by the information on this and related pages.