800XL hangs at blue screen with cursor

[matirwin]

I have recently pulled my 800xl out form the closet (I stored it when it died a few years ago). It initially was starting with the memory test  screen but I have now replaced and socketed all the ram chips (pretty much nothing was socketed so I need to socket each thing I change). It now boots up to the blue screen with the square cursor and hangs there. If I try to force it to diag mode with option key it also hangs at the same spot. If I put a bad mem chip back in I can get it to do the memory diagnostics screen.  Game cartridges seem to work fine as I have tried  star raiders, pacman, donkey kong and can play them ok.  Basic cart was tried for kicks and it hangs at the same blue screen.  I am assuming its one of the rom chips but before I go pulling anything else I wanted to check with others.  I of course dont have spare roms (I do have an eprom  burner) so cant do a simple swap test.  Any ideas?

[+DrVenkman]

If a BASIC cart won’t boot, then the OS ROM is likely bad. Could potentially also be a bad PIA but those fail very, very rarely. Same possibility for one of the 74-series logic chips or the MMU, but I’d start with the OS ROM and see if that gets you back up and running.

[+Nezgar]

@matirwin Since you've done all the tests I can think of, short of swapping an OS ROM from another machine which you indicated you don't have, if you like you can PM me and I can program and mail you a replacement OS EPROM to try...

 

Another remote possibility is bad RAM or MMU... I could send a 2nd chip programmed with Shoestring's RAM tester as well to eliminate that possibility.

Edited August 11, 2020 by Nezgar

[Rybags]

I'd be pulling and reseating (or adding socket for) MMU and PIA.

Though sort of strange that all those games were OK but a Basic cartridge failed.

[matirwin]

Thanks all for the quick replies! I have pulled the OS ROM and then realized I had no 28 pin headers. Luckily amazon had them so I should have that tomorrow. I also have no 27128 eprom but I do have a 27c256 so I assume I can double the rom image and burn it to that ?

[+Nezgar]

9 hours ago, matirwin said:

I also have no 27128 eprom but I do have a 27c256 so I assume I can double the rom image and burn it to that ?

You are correct!

 

Later with that chip you could even do a 2-OS switcher by bending out the highest address pin and tieing it to a switch between +5V or Ground...

[matirwin]

I burnt the rom and I can get the computer to start now without a cart, but not at initial power up, only on a reset. It still hangs on initial cold start.  I also did burn the shoestring ram tester as suggested above by @Nezgarand that passes, as does the built in system check (memory , audio/visual and keyboard all work)  which now starts when I press the option key.  Maybe the power supply is  sketchy and cant give enough juice to get the machine running? I tested it while running and its 4.94v. Not sure what the spec is for these (its just barely  over 5v with it not being connected to the machine). I am going to replace that power supply in either case.  At least it functions (or enough to use)  now. 

[+Nezgar]

@matirwin what speed is your eprom rated at? Faster than 200ns "may" produce random instabilities. But many may also work just fine..

 

Maybe as @DrVenkman suggested, some 74LS chips to try replacing, easily sourced. I'm not sure which specific ones are involved myself. Lastly the PIA or MMU...

 

I could program a GAL to replace the MMU for you for that test...

[ClausB]

I had this same symptom once in an 800. Turned out to be a bad CTIA which thought the START button was pressed when it wasn't and caused the cassette boot process to begin. I had the speaker unplugged and so didn't hear the beep, so it took a while to discover the problem. Substituting a good GTIA solved it.

[Rybags]

Good thought... quick way to abort a tape boot from memory is press Break twice quickly.

[matirwin]

Replaced all the 74ls chips and still same issue. I also socketed every chip while I was at it for more easy testing.  I tried the break key trick also but it seems still stuck at the blue screen unless you reset it a few times then basic runs.  Good news is its no worse after my socket installs.   I did notice something strange (before I socketed everything... still the same after) , the sound works in the self test (all the channels play)  but not in the donkey kong cart (or pac man either). I guess my pokey is bad or failing?  

[matirwin]

Adding to my previous thought. If my pokey is indeed bad , maybe it is trying to boot to a phantom SIO device, that is why a cartridge works fine but it hangs before basic because it thinks it wants to boot a disk?

[+Stephen]

Pretty sure that a machine without a pokey will hang as you describe so I can see a defective one causing this issue.

[matirwin]

It was the pokey that is "flaky". The pokey seemed to work fine  on reset (mostly) but never works correctly on power on from cold.  That is why the sound test passed in self test every time but failed when I tried a cart. To have made it that far to the self test without locking up it needed to do a reset not a cold boot. Same went for the carts to get sound.... they would work also from a cold boot but with no sound. I pulled the pokey from my missile command cabinet to verify (the chip is now back in its home and a replacement has been ordered)  and it starts perfect every time. Thanks to everyone for their help!

[+Nezgar]

Good stuff. Now how does it behave if you put the original OS ROM back in?

[matirwin]

Works fine with original rom back in as well. 

[lbaeza]

Hi matirwin

 

Thanks for reporting this was due to a faulty Pokey. I had exactly the same issue with my 800XL. It started out with a faulty RAM module which I located using Shoestring, and after replacing the faulty module, the computer showed the blue screen and the cursor, but it never showed the READY welcome message. I replaced the Pokey and then it booted without any problems. That PRRRRRRRRRRRRRR sound at boot may sound like a fart, but it's music to my ears now XD  

Regarding Shoestring, I can never stress enough how good is this tool. Man, it's just a matter of burning a 27C128 EPROM with this custom OS and power up your Atari. It will show you exactly what is the RAM module with problems so you can replace it. No need to use a logic probe or an oscilloscope for that matter. Just boot from Shoestring and you're good to go. I really want to thank the author for making this tool available to the community, it really helps to revive our loved computers and bring them back to life. If you haven't installed a 28 pins IC base for your operating system chip, please do so. It is the best decision you can take on your Atari. This opens the door for new and improved operating systems like Shoestring.

 

Kind regards,

 

Luis.

[shoestring]

On 3/1/2021 at 12:53 PM, lbaeza said:

Hi matirwin

 

Thanks for reporting this was due to a faulty Pokey. I had exactly the same issue with my 800XL. It started out with a faulty RAM module which I located using Shoestring, and after replacing the faulty module, the computer showed the blue screen and the cursor, but it never showed the READY welcome message. I replaced the Pokey and then it booted without any problems. That PRRRRRRRRRRRRRR sound at boot may sound like a fart, but it's music to my ears now XD  

Regarding Shoestring, I can never stress enough how good is this tool. Man, it's just a matter of burning a 27C128 EPROM with this custom OS and power up your Atari. It will show you exactly what is the RAM module with problems so you can replace it. No need to use a logic probe or an oscilloscope for that matter. Just boot from Shoestring and you're good to go. I really want to thank the author for making this tool available to the community, it really helps to revive our loved computers and bring them back to life. If you haven't installed a 28 pins IC base for your operating system chip, please do so. It is the best decision you can take on your Atari. This opens the door for new and improved operating systems like Shoestring.

 

Kind regards,

 

Luis.

You're welcome and thanks for your kind comments. I was working on improvements before I lost all my code in a HD crash. In it's current state, not much happens if the RAM chip is complete loss and the logic used for locating the faulty RAM chip isn't very reliable but at least you still get a display ( if RAM is the only fault in the computer and there is no short  ) even with no RAM installed.  

Edited March 14, 2021 by shoestring

[matirwin]

On 2/28/2021 at 8:53 PM, lbaeza said:

Hi matirwin

 

Thanks for reporting this was due to a faulty Pokey. I had exactly the same issue with my 800XL. It started out with a faulty RAM module which I located using Shoestring, and after replacing the faulty module, the computer showed the blue screen and the cursor, but it never showed the READY welcome message. I replaced the Pokey and then it booted without any problems. That PRRRRRRRRRRRRRR sound at boot may sound like a fart, but it's music to my ears now XD  

Regarding Shoestring, I can never stress enough how good is this tool. Man, it's just a matter of burning a 27C128 EPROM with this custom OS and power up your Atari. It will show you exactly what is the RAM module with problems so you can replace it. No need to use a logic probe or an oscilloscope for that matter. Just boot from Shoestring and you're good to go. I really want to thank the author for making this tool available to the community, it really helps to revive our loved computers and bring them back to life. If you haven't installed a 28 pins IC base for your operating system chip, please do so. It is the best decision you can take on your Atari. This opens the door for new and improved operating systems like Shoestring.

 

Kind regards,

 

Luis.

I am glad that this post was able to help you and thanks for shoestring as well for the ram tester as it helped me narrow my issue.  Also the dragonstomper under your username ...   that reminds me I had that cassette when I was a kid for my 2600 and supercharger, lots of great memories. 

Edited March 14, 2021 by matirwin