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VULCAN-74 RETRO GAME COMPUTER

A POWERFUL RETRO GAME COMPUTER BUILT USING ONLY 1980'S LOGIC AND A SINGLE 6502 CPU.


Multiple color hookup wire

Thin hookup wire in multiple colors.

Since my plan is to actually hand wire all 32 of the SRAMs to the DIP sockets, I will require 36 small wires per IC, for a total of 1152 cut, stripped, and tinned wires, no problem! Number 30 AWG wire or slightly smaller works perfectly for this kind of work, and it is available in multiple colors from just about any electronics supply store. 100 feet of this wire goes a long way when you are only cutting one inch sections at a time from it.

SRAM, sockets, and caps

Getting ready to adapt 12 megabytes of SRAM.

25 of the 32 DIP sockets I ordered arrived, so I decided to do them all at once to see how long it would take. Had a flu that day as well, so it was a perfect way to do something useful rather than laying around feeling bad. Shown in the photo are 25 DIP sockets, 25 SOJ SRAMs, and 50 decoupling capacitors with the value of .1 uF (104 marking). I add these to VC and GND pins on both sides of the SRAMs, just to play it safe and help eliminate high frequency switching noise and power spikes.

SOJ package showing pins

The underside of a 36 Pin SOJ package.

J-Lead packages actually have J-shaped legs that curl around to the underside of the IC body as shown here. These are designed to be push down into a mating socket that makes contact from pressure on the side. The rounded bottom of the J-shaped pins help to align the IC during insertion into the socket.

These leads make it quite easy to solder wires to, and can even be hand soldered as surface mounted components onto a mating land pattern. Although the SOJ package has a bad reputation in the industry, I kind of like it, and even use it when making actual circuit boards.

Bending SOJ pins

Bending the VCC and GND pins straight.

My method of socket mounting these SOJ ICs involves bending the VCC and GND rails outwards on both side of the IC so that they can be soldered directly to the socket. This hard mounting of the 4 pins creates a stable foundation to hold the IC so that I can easily add the rest of the wiring.

To straighten the J-lead, use a sharp and accurate tweezer to grasp the very end of the lead and twist it slightly to uncurl just the tip where is curls around to the underside of the IC. From there, it is easy to work the pin the rest of the way straight as shown here. Now your IC pins look like mini DIP pins.

Pins now flat

Bending the pins into a 90 degree angle.

Now I bend the two straight pins outwards at a 90 degree angle so they run parallel to the surface that the IC is sitting on. You can also see in this photo that I have forced the two flat legs away from each other at a very slight angle. This helps mate each pin with the .1” pitch of the socket pins as can be seen in the following image.

Soldering SOJ to socket

VCC and GND pins mated to the socket pins.

Since the pitch of the SOJ pins are half the distance of the DIP socket, the outward parting of the pins helps to align them for soldering. These four pins create the foundation for fastening the IC to the socket, so it’s important that they are secure.

Multiple SRAMS with bent pins

Multiple SOJs ready for socket mounting.

It’s always more efficient to do one operation at a time when mass producing something, so I bent the VCC and GND pins on all of the SOJ packages until all 25 where ready. It doesn’t take long to start getting fast at doing the same repetitive task over and over, but it’s not the kind of thing I would want to do for a living.

Adding decoupling capacitors

Setting decoupling capacitors for soldering.

I always use decoupling capacitors on large ICs such as microcontrollers and SRAMs, even though they are already added to the breadboard rails. For years, I never bother with decoupling caps at all for any design, and everything always worked fine, but once I started doing video generation projects, I did notice slight interference patterns on the screen when not using any decoupling capacitors.

I have also found that the 65C02 CPU is a very noisy beast as compared to something like an AVR microcontroller, so this will help keep interference patterns away from my NTSC video output. Decoupling capacitors are also best placed as close to the IC as possible, so having them built right into the socket like this is the optimal solution.

The legs of the capacitor fit right into the holes in the socket pins, and I left a little extra length so the bodies could be bent over the IC, keeping them out of the way of the wires that will soon be added.

Capacitors soldered

Capacitors bent over the bodies of the ICs.

Once both legs of the decoupling capacitors were soldered into the holes in the socket pins, I bent them over the top of the SRAM body so that they would be out of the way. The capacitors also help hold the IC in place, so it is now secure enough for handling when adding the other 32 small wires.

Multiple SRAMs completed

Socketed SRAMs ready for wiring.

Moving right along, I have all 25 SRAMs soldered to their sockets, each with a pair of decoupling capacitors for VCC and GND on each side of the package. This job didn’t take much time at all, but now the tedious work shall begin, cutting, stripping and soldering of wires, oh so many wires!






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