5200 - 2 port compatibility problems

[+Mitch]

I've been wanting for awhile to figure out why a few 5200 games (pitfall, etc) won't work with most 2 port 5200's. Hampering me is the fact that I only currently have one 5200, a 2 port that is compatible with all 5200 games.

 

I decided to take a look at the 5200 FAQ to see if I could dig up any info about the differences in the 5200 models. I found a listing of differences between the 4 port and 2 port models and decided to compare them to my 5200. I found a couple differences.

 

The FAQ says:

 

4.10 - 2-PORT PRODUCTION MODIFICATIONS

--------------------------------------

 

There are three production modifications to the logic board of 2-port

5200 systems. A number of people have seen these mods on their 5200s

and the mods appear to have been factory installed.

 

*(two points cut)*

 

3. A wire is run from the feed thru below C94 to A27 pin 1, pin 1

and 2 of A27 are connected together on the back of the board, pin

10 of A15 is lifted, and connected to A27 pin 3. This

modification alters the timing of CAS to the dynamic RAM.

 

OK, the parts that are in bold are where I have a difference. On mine the wire is run from the feed thru hole below C99 not C94. I took a quick look over the board and I couldn't even find a C94. Also, the pin on A15 that is lifted and wired to, is pin 11 not pin 10.

 

I was looking over the rest of the FAQ and I saw this part:

 

Later releases of the 5200 incorporate some minor hardware changes.

(snip)

Also, on power-up, the monitor

program checks for the PAL version by examining the GTIA register PAL

after step 2 of the initialization routine. It also checks the

cartridge program for PAL compatibility. The byte at $BFE7 should

read $02 if compatible, or $00 if not. This is the only important

change to the monitor program.

 

So, apparently there is a difference in the OS chip between the 2 port and 4 port. Then I noticed this:

 

A8 C019156A ROM BIOS

 

The A8 chip on my 5200 is CO19156-05 and is dated 1982.

 

Now what does this all mean. The first two differences could possibly be typo's in the FAQ but the difference in the OS chip is more interesting. Apparently the standard 2 port OS was changed from the 4 port OS to add PAL support. However, on my 2 port the OS chip is dated 1982 and lacks the "A" at the end of the model number. Apparently I have a 4 port OS in my 2 port 5200! The different OS may be what is causing the compatibility problems in the 2 port.

 

Can someone with different 5200's models verify these results?

I am very curious now to see if the different OS is really what is causing the problem.

 

Mitch

http://atari7800.atari.org

[Charlie_]

Mitch, you are the man!

 

Let me explain........

 

Today I received in the mail 2 atari mod kits for 4 port 5200s. I installed them. (What a pain in the ass.) Both 4 ports now work with my VCS adaptor. I'm a happy guy. But not happy enough. I too have a 2 port system. Mine did not run pitfall.

I had read your post before I checked the mail this morning and got into this whole moding the 4 port deal. And it was bouncing around in my head that I had a blown 4 port system in the attic. (sucked too it had a * serial number) So after both 4 ports were up and running every thing, I said why not swap the bios from the broken 4 port to the 2 port like mitch was talking about. I was already "in the grove" from having my head in 5200s all day.

So I opened my 2 port. Just like the FAQ claims, my 2 port had a bios with the "A" on it. I pulled the broken 4 port out of the attic and swapped the bios chips.

BAM!! It now runs pitfall!!!!

 

So thats the answer. It's the bios chip that causes compatibility problems with the 2 port systems.

Thanks! Now all my 5200s are 100% compatible.

 

Geez, with all this work I did today, I think now I might actualy sit down and PLAY one of these systems. :-)

 

Charlie

[+Mitch]

quote:

---

my 2 port had a bios with the "A" on it. I pulled the broken 4 port out of the attic and swapped the bios chips.

BAM!! It now runs pitfall!!!!

---

 

Great! I'm glad to hear that my theory was correct. I guess I should email Keita and see if he's interested in incuding this info in the 5200 FAQ.

 

Mitch

http://atari7800.atari.org

[Genki]

So basically you could swap the BIOS to make newer 5200 system play all games? And that the BIOS are not related to VCS adapter?

 

How sneaky... that's what Mattel Electronics did to Intellivision to "fix" it so Coleco games wouldn't work. And that "fix" has nothing to do with the 2600 adapter. You can modify any other Inty system to work with the 2600 by modifying the pin 2 of cart port so it feeds to the RF modulator. I believe the full details are on Blue Sky,

[+Mitch]

quote

So basically you could swap the BIOS to make newer 5200 system play all games?

 

Yes.

 

quote

And that the BIOS are not related to VCS adapter?

 

Yes again.

 

The reason for the new OS was because Atari was planning on making a PAL version 5200 (a prototype exists) and it needed a new OS to check whether an NTSC or PAL cart was inserted. They probably didn't check the 3rd party games for problems, just their own. I doubt it was intentional.

 

Mitch

http://atari7800.atari.org

[Tempest]

I'm getting two PAL 5200 prototype cartridges soon (Star Raiders and Missile Command), but I didn't know any PAL 5200 prototypes existed. I'm not exactly sure if thee are going to be any differences in the carts themeselves (I doubt it), but they clearly say PAL on the labels. I'll let you know when I get them.

 

Tempest

[Charlie_]

>And that the BIOS are not related to VCS adapter?

 

Yeah, the bios has nothing to do with the VCS adaptor. In fact the busted 4 port I took the bios out of, would run the VCS adaptor but nothing else!! :-)

Getting the VCS adaptor to work on older 4 ports with Atari's mod kit is a major pain. I'd say about a dozen things to solder. You need to break a plastic pin off the inside top cover. All that is not to hard, just time consuming. The hard part is cutting the trace to isolate pin 24 of the cart slot. Its a fat ground trace, and half of it is under the slot. You have to be careful not to cut it for pins 23 and 25 that are very close to it and share this trace.

 

Charlie

[jsoper]

Great job on the detective work guys!

 

Seems like both the 5200 and 7800 compatibility problems involve Activision cartridges.

 

What does everyone think? Was Atari QA too stupid, too lazy, or too arrogant to verify their stuff with 3rd party cartridges?

John

[Charlie_]

Actually, the 7800 issue I know of is with the M network cart Kool-Aid man. This cart also does not work correctly in a Coleco Gemini. It does work right in the 5200 VCS adaptor.

There are other games that do not work with the 7800 but I don't think they are activision...(?)

 

Charlie

[jsoper]

Robot Tank, Space Shuttle, Decathlon

 

It's all in the FAQ

John

[Charlie_]

ah, ok. The 3 I don't have. :-)

 

Charlie

[Genki]

Also some models don't work with Supercharger (and presumably Cuttle too) and I've heard of instances where Dark Chambers for 2600 won't work on 7800.

[+Mitch]

I just checked with Brad of Best Electronics and he says that they have the original 5200 4 port OS available for $5. I thought I'd mention that in case anyone wanted to upgrade their 2 port system for full compatibility. Their minimum order is $15, I believe.

 

One note to the 5200 homebrew guys. Are you checking to see if your programs will run on the standard 2 port? If you're not, it may be something to consider.

 

Mitch

http://atari7800.atari.org