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SeaGtGruff

A couple of questions for the engineers

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I downloaded the free LTspice IV program a couple of years ago, thinking to use it to build a simulation of the TIA. Not being an engineer or electrician, I quickly found that it was WAY over my head. Specifically, I had virtually no clue about what to enter for the different parameters-- for example, it's very simple to pick a resistor and put it on your schematic, but you either need to pick an existing resistor from the library or enter the resistance, tolerance, and power rating yourself. Fortunately, I found some of this information in the parts listing included in the 2600 field service manual-- for example, it lists the resistance and power rating for each resistor, but says nothing about the tolerance. I was thinking that if I knew who manufactured the parts (or equivalent replacements), it might help me find existing definitions of those parts that I can download and use with LTspice IV. Does anyone know specific present-day companies that make resistors, capacitors, transistors, etc. that can be used as replacements for the Atari 2600's parts?

 

Second, I recently decided to model the 2600's oscillator from the schematic for the 2600 (as opposed to the 2600A, which uses a simpler design for the oscillator). I chose the XTAL symbol for the crystal, but have no idea what the parameters should be. LTspice IV needs to know the capacitance, voltage rating, RMS current rating, equivalent series resistance, equivalent series inductance, equivalent parallel resistance, and equivalent parallel capacitance. Holy cow! All the parts list says is that it's a 3.579575 MHz crystal.

 

I'd already given up on trying to model the TIA schematics in LTspice IV, and resorted to using an Excel spreadsheet to model the TIA-- which works pretty well for what I wanted; the biggest hurdles were teaching myself how to read and understand the schematics (which I've gotten reasonably good at), and figuring out how to eliminate problems caused by circular references (which I was able to do). My spreadsheet simulations don't show any timing delays due to signal propagation delays or gate delays, but they do let me follow the flow of the signals and see how everything works.

 

Now I decided to take another stab at learning to use LTspice IV to model the oscillator and the sound filters on the motherboard. At the moment my primary interest is in the sound generation, and I've got all the relevant portions of the TIA done in Excel spreadsheets, but I'd like to graduate to LTspice IV if possible, and I figured the oscillator would be a good place to start-- because it really is where everything starts (since the signal that feeds into XTAL or OSC-- TIA pin 11-- is used to get the PHI-0 signal, CLK signal, H-PHI-1 and H-PHI-2 signals, etc.), and also because the oscillator circuitry is fairly small and self-contained (I'm not sure about where the oscillator circuitry and the color delay circuitry are joined together, but they're separated in the 2600A design, so I'm just going to leave out the color delay stuff). Even if I decide to just use the 2600A schematics (I'd actually like to model the oscillator for both the 2600 and 2600A for comparison), I still need to know what the parameters for the XTAL symbol should be, and that's where I'm stuck.

 

Any suggestions or guidance would be appreciated-- although this project is just for fun, so if I can't get it off the ground because it's too much for my meager abilities, then no biggie! ;)

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