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Dizzy

Atari 800 strange problem ...

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Hello,

 

I just bought an Atari 800 (PAL). But it has a problem that I cannot explain : if I turn it on with a game cartridge inserted, then the game works perfectly.

But if I turn on the Atari with no cartridge inserted, or with the BASIC cartridge in the left slot, then after some seconds of usage the Atari crashes ...

I tried to swap the RAM and ROM boards with another 800, but the problem remains ...

 

Does anybody know where my problem comes from ?

 

Thanks !

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Might be a problem with memory selection. Game cartridges will tend to only use the first 16K of Ram. The first Ram slot grabs whatever Ram select lines it can handle and passes spares onto the next and same for slot 2 to 3.

 

Can you load disk games with real drive or via SIO2PC etc?

 

Have you tried with only one or two Ram modules present - try just 16K if possible.

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Yes, I have already tried with only one 16k module, but still the same ... I also tried to boot on my SIO2SD, but while the game is loading I get random crashes ...

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I tried Pacman, and a chess game, they both work fine. I just disassemblied the Atari, cleaned every connectors, pushed every chips in their sockets, but still the same ...

Edited by Dizzy

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I already tried to swap the OS ROM with another 800 (see my first post), but still the same. It crashes after a few seconds of use with notepad, basic, or while booting on a floppy disk. But I have not problem while using game cartridges ...

 

EDIT : most of the time, when I am using BASIC or NOTEPAD, in both cases the Atari crashes once I pressed the "RETURN" key. I can type many letters with the keyboard, and the Atari works fine until I hit Return.

In some rare cases, the Atari crashes right after having powered it on. I saw someone else message saying he has the same problem but with no answer ( http://www.verycomputer.com/10_c361dd63d484781d_1.htm).

Edited by Dizzy

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Sorry I missed that.

 

Since you have access to another 800, you can try swapping the main board and CPU board. Eventually you'll find out which board is responsible, and then you can start swapping chips until the problem moves to the other board.

 

It could also be caused by the power supply/IO board.

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Thanks for your answer, I guess I will have no other choice than trying, like you said, to swap everything from my working Atari to the bad one. But my working Atari 800 is a NTSC one, my new 800 which is not working is a PAL one ... So I guess some compenents are not swapable, and I do not know which ones ... And my fear is to break some components of the working NTSC 800 ...

Edited by Dizzy

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So here is my first swaping test result : the CPU board swaped solved the problem, but now I have colored stripes on the screen. I guess this is due to an NTSC GTIA/CTIA connected to a PAL motherboard ... I hope the problem does not come from this chip or I will have to find a working PAL GTIA chip ... Now I will swap all CPU board components to see which one is failing ...

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Yes, Antic and GTIA are unique to each system and you can expect strange results when swapping into a foreign machine.

 

My guess would be the CPU, second guess would be Antic.

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I replaced the CPU, but it's very strange : with the NTSC 800 CPU into my PAL 800, it displays a brown screen when powering it on. Very strange, I cannot understand why the CPU is not working in the PAL version, as there should be no change to the CPU if the 800 is NTSC or PAL ... I will now try to swap some other components ...

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Sometimes it's easier to try suspected components in a known good machine. Maybe try the Pal machine's CPU in the NTSC machine. Then try it's Antic at the same time.

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Here are the results of my tests : Antic and GTIA are working fine, I also swapped the 74LS244N wich is also working fine. The only untested chip is a 74LS74ANDS which seems to be specific to the PAL version.

The strange thing is when I swap the CPU from a NTSC 800 to the PAL 800, then the PAL 800 displays a brown display at startup ... I really cannot explain that, was there a specific 6502 for the NTSC version and for the PAL version ? I cannot imagine that ...

I think I will now try to take a 6502 from another computer (Apple II ?) and see what happens ...

Edited by Dizzy

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Don't do the 6510 swap from a C64 - they are very different and won't work, in fact might fry something.

Atari CPUs will either be 6502C which is the custom CPU only ever used in 5200, late 400/800, XL and later and the 7800. No other computer used it.

Earlier 400/800 use a 6502B which is the 2 MHz version of 6502. I think the 6502 from Vic-20 is the same pinout but probably the "A" 1 MHz version.

 

How do you mean brown screen? Sometimes the background colour will be dark brown on powerup but the operating system very quickly changes all colours to black on the 800, on XL/XE it has a delay so takes longer.

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Thanks for the advice, in fact I saw it was a 6510 and then didn't do anything with it. I then thought about swapping it with an Apple II, but the Apple II 6502 is running at 1Mhz only, compared to the 2Mhz of the 800 (as you said) ...

If I swap the 6502 of my PAL ATARI 800 with the 6502 of the NTSC ATARI 800, then when I power up the PAL ATARI 800 I get nothing else than a brown screen which is displayed forever.

As I have two different NTSC ATARI 800, I tried the processor swap with both of them, but still getting the dark brown screen ...

 

EDIT : you were right for the VIC20, only 1Mhz ... So I really don't know what to do now, as I do not have any spare PAL 6502 for ATARI 800 ... Damned !

 

Does anyone know where I could buy a PAL Atari 800 CPU board ? I can only find some NTSC versions on EBay ...

Is the Atari 400 CPU board compatible ?

Edited by Dizzy

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Some Apple II CPUs are the 2 MHz variety.

 

You need to be careful with CPU swaps on the 400/800. Check the code to ensure you're using the same type...

 

CO14377 (6502B - used in most 400/800 models - standard 6502)

CO14806 (6502C - used in some later 400/800, 5200, 7800, XL/XE models - "Sally" custom variant which was designed to allow Halt condition without need of logic support chips)

 

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Thanks a lot, I'll check that ... But can I use a 6502C into an ATARI 800 (not XL) which had a 6502B ?

Edited by Dizzy

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Does anyone know where I could buy a PAL Atari 800 CPU board ? I can only find some NTSC versions on EBay ...

Is the Atari 400 CPU board compatible ?

You don't say where you are.

 

Best Electronics www.best-electronics-ca.com

 

408-278-1070 1:30 PM to 5:30 PM Pacific time

or maybe

B&C Computervisions

 

http://www.myatari.com

 

530-295-9270 11 to 4PM PST

both in California

 

 

Best has:

400/800 PAL / UK CPU Board

with CO14887 + CO14889 PAL I.C.s

CO14806 MPU IC and support chip

 

is:

CA015967 or CA06113.

 

 

I'm not familiar with UK/Germany/EU companies.

You can look in the Atari8bit FAQ and get EU companies.

 

http://faqs.cs.uu.nl/na-dir/atari-8-bit/faq.html

Edited by russg

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Thanks for your answer (I am in France but I can order anywhere in the world if they do international shipping). But I finally swapped my PAL ATARI 800 6502 with a PAL VIC20 6502, and I have the exact same result as when I swapped the CPU with an NTSC ATARI 800 :

brown screen on power on ...

So now I am pretty sure that there is no NTSC or PAL 6502. There is only one 6502 processor for both PAL and NTSC version (which is very logic to me).

 

So now here is my very strange situation :

 

- If I use the original 6502 of my PAL Atari 800, then after a few seconds of use in Basic or notepad, or while booting a floppy, it crashes (and the reset button don't even work). But it works fine using a cartdridge !!! (????).

 

- If I use the NTSC 800 6502 in my PAL 800, then it just display a brown screen at startup ...

 

- If I use the NTSC 800 complete CPU board in my PAL 800, then it works fine except it displays colored stripes (wich is probably due to the NTSC / PAL differences). So this confirms the problem comes from my PAL CPU board, but according to my different tests, the problem is not coming from the ANTIC, GTIA, or 74LS244N.

 

So the only possibilites are that the problem comes from :

 

- the 6502, but why other working 6502's are working worse than the original 6502 in my PAL CPU board ?

 

- the 74LS74ANDS, but I have no spare part to try.

 

- an electronic component like a resistor for exemple, but my knowledges in electronic are too low to know how to test them ...

 

So I feel a bit desperate, as my only solution would be to buy a PAL CPU board .

Edited by Dizzy

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But you still have not answered Rybags question, do you have a 6502C on one of your CPU cards? A 6502B will not work in the spot of a 6502C definitely. Whether or not the 6502C will work in the spot of a 6502B depends on whether the board just so happens to be wired correctly. It's more likely that a PAL CPU board has a 6502C than an NTSC board to have one, since PAL were generally released later, and more likely to have additional revisions over the NTSC versions.

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Thanks for your answer. Here is what is written on my 6502 :

 

MOS

CO14806-6

0282

 

I guess my 800 was a "recent" one as on the box there was a sticker "Now with 48K". So it's not one of the first releases.

The 6502 chips I have on the NTSC CPU boards are 6502B. So you are right : my processor in the PAL 800 is a 6502C. This surely explain why when I was swapping my 6502C with a 6502B I had a brown screen ...

Now I need to find one. I have some Apple IIe with a 65C02 processor, but I guess it is not the same as 6502C, right ?

Edited by Dizzy

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Thanks a lot, I'll check that ... But can I use a 6502C into an ATARI 800 (not XL) which had a 6502B ?

No, they have a different pinout. A 65802 (if you can find one) will work in place of a 6502B, but not a 6502C (C014806)

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You have 2 different types of CPU board:

 

This is the old style (uses standard 6502 CPU):

 

atari_800_%20027a.jpg

 

On the left is the new style (uses 6502C/Sally CPU):

 

Atari_400_CPU_board_and_RAM_card.png

 

You cannot swap the CPU from one to the other, but you can use an XL/XE/7800/5200 cpu in the new style board.

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Thanks a lot ! My PAL 800 board is the one from the bottom left in your pictures.

So I cannot replace a 6502C by a 6502B, but can you confirm that I cannot also replace a 6502B by a 6502C ?

Unfortunatly I do not have any XL/XE computer ...

Edited by Dizzy

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