RETURN key on 800XL causes reset

[RETURN key on 800XL causes reset]

How about pulling ALL the socketed chips and measuring resistance on all address and data lines between +5 and GND? If one line shows a different measurement from the others, start checking the resistors connected to that line. Of course, compare address lines and data lines separately.

 

It could be a bad pull up on a single line, or some models have resistors in series with the RAM chips. If one is open, all kinds of strange things could happen.

Thats sound like good idea. I will do that as soon as i find some idle time.

[RETURN key on 800XL causes reset]

Was 'Zorro' a cart, or from disk? How about BallBlazer? This acts like a cart interface problem - sorta...

 

Bob

It was loaded from the disk

[RETURN key on 800XL causes reset]

Recap of what was done:

 

1. Replaced all the big chips including ROM from a working system
2. MMU has been swapped
3. Memory chips have been installed from a working system
4. Different keyboard was used
5. Address lines verified from CPU to Memory addressing chips
6. Re soldered address line joints
7. XL self test shows good
8. SALT RAM test shows good
9. Basic XL gives error -14 when hitting enter.
10. Mac/65 gives an inverse-heart symbol, syntax error
11. Ballblazer came up and looks normal
12. Zorro booted and played music, but the screen was corrupted...

[RETURN key on 800XL causes reset]

I have nothing useful to add here, but wanted to send kudos to MrMartian for hooking up personally with a fellow Atarian in order to help them out!

 

Whattaguy :-)

 

I've never heard of an 800XL suddenly developing such a fault, but if it's newly-acquired then here's my dumb diagnosis! Maybe the previous owner had the Return key hard-wired to work within a custom application/bit of hardware that's no longer there? Like one of those Atari-driven broadcast character generators that depended on bits of bespoke hardware hanging off the SIO? A hacked OS coupled with some crude soldering could ensure pressing Return jumps to a specific memory address (but now borked as its not being used as intended with BASIC commands in the buffer) or to poll missing hardware..? Probably pure fantasy! In any case, hope you get it sorted :-)

I have used different keyboard. The solder joints on the board look clean and untouched. I have also re-soldered address lines from CPU

[RETURN key on 800XL causes reset]

If you hadn't told me that memory test was OK I would have insisted that this was a RAM issue.

 

Which makes me wonder: Is there any chance that a faulty RAM giving you a false positive (green square)?

 

If your RAM is socketed, I'd still replace them all just to be 100% sure.

I have swapped the ram from working Atari.

[RETURN key on 800XL causes reset]

You wrote big chips... did you also try the PIA?

 

Port B is involved and perhaps unstable. That's the PIA.

Yes i have replaced PIA and MMU

[RETURN key on 800XL causes reset]

I'm in Woodstock, and have many spare chips.

That would be great, i could stop by after Wednesday (short drive from London) bring the board and check it.

[RETURN key on 800XL causes reset]

 

The MMU decides whether you have no cart, an internal cart, or an external cart in your system. It also decides whether you are addressing RAM, ROM, I/O, or cart. If it gets confused, you will crash at some point.

 

Since 'no cart' seems to work, the addresses from the CPU are probably OK and ANTIC/GTIA are behaving. You have done POKEY. It's possible that the 6520 is flaking out, more likely is MMU.

 

Bad MMUs are pretty common.

 

Bob

I have tested the big chips on other board and vice versa and all of them are performing fine. I will try the mmu

[RETURN key on 800XL causes reset]

I would go with the MMU. Something is broken when you address cart space.

 

Bob

When i run basic from the rom chip it behaves the same way as if i ran the basic from cart. Would that still be a valid statement?

[RETURN key on 800XL causes reset]

Outside chance you're in the northern Ohio? I have a socketed test board.

Thanks for the offer, I am in ShothWestern Ontario

[RETURN key on 800XL causes reset]

MMU

U3 CO61618, in the center, straight above the center CPU U8, 20 pin chip, longer one.

I will have to source one up to test it. Most of my chips on this board are in the sockets. But my working system has them soldered in.

[RETURN key on 800XL causes reset]

How can it be the keyboard, unless the return key somehow is shorting power to ground, or some other very strange thing. I guess anything is possible, but this is unlikely.

I would suggest trying a different keyboard if one is available. Hopefully, a friend will loan you one for testing.

I have already tried different keyboard, ram, and POKEY chip with no luck.

[RETURN key on 800XL causes reset]

Very strange. What happens if you turn it on with no cart and the option key held down during power up? That should take you to the self test menu. If it does, try running the tests.

All the tests in diagnotics are passing green.

[RETURN key on 800XL causes reset]

press the SELECT key and the RESET key together. release both then press the Enter key.

This causes system to freez with blue screen and READY displayed, but no reset

[RETURN key on 800XL causes reset]

What exactly do you mean by "code dump"? Stuff on the screen? Please attach a picture if possible.

Do you have any cartridges other than BASIC?

Try typing ?FRE(0) and pressing return. Try typing BYE and pressing return.

What happens?

Typing FRE(0)+RETURN creates white screen

BYE+RETURN black screen

Running basic from catriage i cant not reproduce the "code dump" and pressing RETURN key causes reset to black screeen

[RETURN key on 800XL causes reset]

I only have the computer, no floppy or tape yet. When I have basic cartridge inserted the RETURN key does not reset the system but produces a code dump

[RETURN key on 800XL causes reset]

I am looking for help/pointer how to fix my 800XL. The symptoms are very strange. The computers powers on and displays “READY” you can type anything and everything is fine until you press the ENTER key then the system resets to a black screen and freezes. I have tried different keyboard but no luck, build in diagnostics is green. Any help would be appreciated.