Ben_Larson

It could be a bad STIC chip as others said. But don't go trying to find a replacement just yet because first you'd have to get the RF shield off the board which isn't exactly simple. That's because the way it's designed is fairly idiotic - the two halves of the RF shield are soldered on. So you'd need a good soldering iron (i.e. 60+ watts) plus a screwdriver to pry with, or else a dremel. It's a real pain.

I think temperament is probably more important than age. Programming in ASM is tedious and debugging is often times hard as hell. I still get tripped up all the time. You really need to be the type of person who enjoys challenging yourself and sometimes spending hours trying to get some small thing working all for the 'aha' moment at the end when you finally figure it all out and it works. The best approach might be to start with batari BASIC and experiment with some inline ASM like KevKelly said to see if it's for you.

You can do it exactly as you said by just using the fine positioning to move the sprite around. That's how the designers intended the hardware to be used and that's perfectly fine ...if you don't plan to reuse sprites. If you do want to reuse sprites, though, then you will need a function to do sprite repositioning. Now why do the tutorials introduce the sprite repositioning function right off the bat? I'm guessing it's to make things easier, because if you use that function, then all the details of rough and fine positioning are abstracted away - all you need to do is set an X value for your sprite and call the function. But, as you've seen, if you actually delve into the function and try to understand the internals of how it works, it can make your brain hurt. Hope that helps.

walldog you and I think alike. I ordered some very small 25mm case fans for this same purpose to experiment with (not a lot of room in the case so I went as small as possible). I installed one in the location you did, and the other one down near the switch. Mine are definitely not 10cfm though. Probably more like 2 each. But I also didn't reinstall the RF shield, so that probably helps...

Hey guys, Picked up my first ever Intellivision I at an antique mall recently ('antique' in air quotes maybe but that's another story... ). Unfortunately when it plugged it in, it would work fine for a few minutes and then glitch out and freeze. Or sometimes the screen would blank out completely. After doing some research, I determined it was probably either a bad RA-3-9600 RAM chip or bad STIC chip. So I bought a donor Intellivision II unit and started swapping parts - turned out it was the RAM chip. I couldn't help but notice when I was inside the Intellivision I, how badly designed it seems to be compared to the Intellivision II. There's a giant RF shield, plus the plastic tray on top of that, but most egregious of all (to me), the motherboard faces down instead of up. This seems like a great recipe for trapping heat considering circuit boards are usually made from insulating materials. Is it true that the Intellivision I fails more frequently than the Intellivision II? (if so I think I can see why) Did I just get unlucky or is it pretty common?

I was actually able to salvage 3 of them using JB weld. The shrink tubing is a good idea, though. On 2 of the posts I fixed, even the first round of epoxy wasn't enough because when I inserted the screws, the posts promptly cracked again. For the second round, I left the screws in and added more epoxy where it cracked. That seems to have worked.

Looks pretty good. I have a 'brittle case' 7800 where most of the internal screw posts broke off. It's very strange because I have another unit made the exact same month and year (I think) and that one isn't really brittle at all.

You are right that the R/W signal is not exposed on the cartridge connector and that actually complicates things a lot on games that have extra RAM. The way it's solved is that the RAM read addresses are different from the RAM write addresses. In that way, the cartridge can determine if an access to the cartridge RAM is a read or a write. It's wasteful because it means that twice as many addresses are needed. So on a Superchip game, for example, 256 bytes at the beginning of the 4K ROM space are wasted for access to the 128 bytes of RAM. That means there's only 4,096 - 256 = 3,840 bytes available for program data in each bank. As for how they actually generate the signals, I think that's done internally on the Sara chip. If you wanted to do your own implementation using discrete logic, you would need to implement the glue logic to generate the /WE and /OE signals when a read or write address was decoded. I don't think the timing is necessarily as critical as you think, though. For a write, the data just needs to be present (and held steady) within some window of time after the control signals are set.

I wonder if terrible 2600 output is mainly a problem with the later 7800s then, because both of my 7800s are later model versions without an expansion port. I had an expansion port version 7800 when I was a kid, and I don't recall ever thinking that the output on the 2600 games was especially lousy.

Yea sorry, I guess I didn't really clarify that very well in the first paragraph. I'm only referring to the video output of 2600 games on the 7800. The mods I did only affect the TIA (2600 video chip) output - they shouldn't have any effect at all on the video output for 7800 games.

When I plug in my 2600 Jr., the output is really good. It completely puts my 7800s to shame. It's vibrant, bright, and sharp. Both of my 7800s are dull, not bright, and blurry. It's night and day when you look at them back to back. In fact, I got so irritated about it this last weekend that I decided to start tinkering with my 7800. Surely it must be possible to improve it, right? Well here's what I've come up with after a week or so of messing around with it and reading things online (please try these at your own risk btw - I am a shadetree electrical engineer at best ) Mod 1: Add resistor to TIA pins This mod involves adding an 820 ohm resistor between pins 6 and 9 of the TIA and was apparently added as a design change to the 2600 at some point (it's mentioned in the 2600/2600A Domestic Service Field manual tech tip #4). I'm not sure the exact history of the design change because the resistor seems to be present on one early model 2600 schematic I found, but then it seems to disappear on a later one, only to then reappear again (?). Some people on a previous thread here on AtariAge mentioned that it worked for them on their 7800s but someone else said it didn't (?). Well I tried doing it on mine and it dramatically improved the color output: Mod 2: Add piggyback resistor to chroma output Some other threads I found on here mentioned the chroma circuit as a source of the poor output, specifically R16 and R17 on the schematic. According to one of these threads, these resistors are present to prevent interference between the TIA and MARIA chroma output. I don't think this is the case actually, because as far as I can tell, each of them go into a high impedance state (i.e. become disconnected) when the other is active. I just tried adding a piggyback 1K ohm resistor to R17 to improve the TIA's chroma signal strength and it significantly increased the sharpness of the output: It did not have any effect I could see on the video output of 7800 games. I did find that if you go too low on this resistor value, though, it causes crackling in the 2600 sound output. I am guessing that's because when the chroma signal becomes too strong it starts to interfere with the sound signal. I don't think this mod excessively loads down the TIA chroma output, but that was my main concern before doing it. So that's what I've done so far - 2 resistors. But it seems to make a big improvement. Still not quite as good as my 2600 Jr but much closer. Does anyone else have experiencing messing around with the video output (other than the composite video mods)? Obviously it's possible to get better output even over RF since the 2600 Jr does it.

@vhzc Was it written in asm? There's 6502 disassemblers out there if you wanted to try to disassemble and get back to the source (assuming it is ASM and not C or something else).

I've probably been staring at old arcade schematics for too long but it seems like something like this might be solvable in hardware by tying an address line to a bus transceiver to disconnect the ARM when the 6507 is accessing RAM/TIA space. I'm not even sure if we're talking about existing hardware or new hardware at this point, though.

I don't know if this joke has already been made and I'm not willing to wade through 41 pages... ...but I am pleased to announce Knight Rider 2600: The Atariage Thread: The Game coming soon.

I was actually just watching this video the other day of the Atari 2600 version of Tomcat. It's really really impressive - nearly as good as the 7800 version IMO: