Multicart problems, again...

[WaverBoy]

So, as I mentioned in a previous post, I recently bought 2 multicarts for the Atari 2600, from different vendors. Both suffered from picture distortion in exactly the same way: weird lines of texturing. Regular Atari cartridges play fine on my system. Paul Slocum replied to my post and said that it's because the carts don't have RF shielding, and that no homebrew carts have it. My question for that response is, why not? One of the carts I got from 4-Jays, and I sent it back to have them test it out, and possibly replace it. Here's the response I got back from them:

 

"Hi,

 

The cart tests good. The problem is that your system is not adjusted to the original specs so that occurs. Have sold over 100 and only had 5 with this trouble. 4 units were replaced or adjusted and worked okay. Will send you a refund with shipping as a good gesture."

 

Now, what's up with that? Could my Atari 2600 really be out of adjustment? If it is, why would it play normal Atari cartridges just peachy? And again, if it is, how would I go about adjusting it properly?

[ussexplorer]

Old electronic stuff is interesting. When it comes to interference you can have a ball. At least they are aware of the problem and it is great they wil offer you a refund. As for adjustment, yes it could be. If you find out what to adjust make sure you mark it. Just in case you need to change it back. I was wondering if tinfoil around the cart/board (Be sure not to ground anything out) would sheild it. Perhaps somebody has a better idea. I asume the metal sheilds they are talking about go around the rom itself. You could find one but make sure it doesn't ground out on anything.

 

Later,

 

Josh

[Albert]

We've sold quite a few 2600 homebrew games through our store and I have not had anyone say anything about them being worse in terms of reception than typical 2600 games. It could very well be happening with some people, and perhaps the problem isn't severe enough for them to complain. I use Coaxial to RCA Adapter with my systems and this seems to help eliminate much of the interference (which seems to be coming from the RF Switchbox).

 

If you're only having a problem with multi-carts, maybe it's something inherent in the design of the multi-cart? Have you tried these carts on another 2600 system to see if they exhibit the same problem?

 

..Al

[WaverBoy]

Yeah, I got one of the adapters at Radio Shack so I could get rid of the switchbox. So, the switchbox isn't the problem. Paul Slocum's assertion that homebrew carts have no RF shielding is troubling me...why don't they have it? If original Atari carts had it, and the homebrew carts are built inside the original shells, why don't they have RF shielding as well? If they can't use the original RF shielding, couldn't new shielding be fashioned?

 

Re: problem being because of the design of the multicart, I thought that might be the problem, but as I said, the carts were made by different people, and one holds 256 games, the other holds 128. Then Paul mentioned the RF shielding factor, and now I really don't know what to think. Surely, if my system is out of adjustment, it would show these same problems on my regular Atari carts...unfortunately, I don't have access to another Atari 2600 on which to test the multicarts. Perhaps I'm the only crazy in town who has one.

[moycon]

I have several homebrew and repo games I'll assume without the RF shield and they play fine in my system.

[Albert]

If original Atari carts had it, and the homebrew carts are built inside the original shells, why don't they have RF shielding as well?  If they can't use the original RF shielding, couldn't new shielding be fashioned?

 

I was always under the impression that the RF shielding on Atari's 2600 carts was overkill. I don't even think most (any?) third-party manufacturers shielded their carts. Atari's RF shield (I'm looking at one now) is actually *soldered* to the board and fits cleanly over the ROM chip. While this shield could be desoldered from Atari's boards and new 2600 PCBs could be designed to accomodate it, it would only work with 2K/4K games which use chips that are the same physical size. 8K+ games use larger EPROMs, and they also typically have chips on the opposite side of the board, which would necessitate shielding on the opposite side as well.

 

Since the lack of RF shielding has not caused any evident problems, there is no reason to pursue RF shielding on homebrew carts. It would just add further cost, time and complexity to building homebrew carts, and it already is a fairly labor and time intensive process.

 

Re: problem being because of the design of the multicart, I thought that might be the problem, but as I said, the carts were made by different people, and one holds 256 games, the other holds 128.  Then Paul mentioned the RF shielding factor, and now I really don't know what to think.  Surely, if my system is out of adjustment, it would show these same problems on my regular Atari carts...unfortunately, I don't have access to another Atari 2600 on which to test the multicarts.  Perhaps I'm the only crazy in town who has one.  

 

If you're only seeing this with multicarts and not normal homebrew games (do you have any?), it could very well be that the more complex circuit employed by the multicarts is generating more radio interference. But I'm not an EE, so I'm only speculating on this point.

 

..Al

[Paul Slocum]

Paul Slocum's assertion that homebrew carts have no RF shielding is troubling me...why don't they have it?

 

Same reason we homebrews don't use mask ROMs: Companies in the 80's had the money to have custom parts like those fabricated. When companies sold thousands or millions of carts that was one thing, but now we're talking quantaties of usually less than 100 and they're hand assembled. And like Albert said, it usually doesn't make much difference.

 

The Multicarts you're talking about are no different from a regular homebrew. They just have a larger EPROM with switches on the high address lines.

 

Some TVs and some Ataris are more prone to interference. Which model of 2600 are using? The Jrs tend to the have the most interference, while heavy sixers tend to have the least.

 

-Paul

[WaverBoy]

Thanks guys for the info. Paul, I've got a 4-switch woodgrain 2600, the same model I had as a child (sigh). But, could it be that 4Jays is right? Perhaps mine is out of adjustment? If so, what settings are there on it to adjust, and is it something a layman like myself could do?

[+Mitch]

Thanks guys for the info.  Paul, I've got a 4-switch woodgrain 2600, the same model I had as a child (sigh).  But, could it be that 4Jays is right?  Perhaps mine is out of adjustment?  If so, what settings are there on it to adjust, and is it something a layman like myself could do?

 

It could be the RF unit in your 2600 is slightly out of calibration. It's that little metal box inside your 2600. You need a plastic hex screwdriver to adjuust it.

 

Mitch