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When 800xl only works with BASIC chip removed...


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#1 seastalker OFFLINE  

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Posted Sat Jul 15, 2017 7:11 PM

FINALLY got my problem 800xl board running... EXCEPT it only works with the BASIC IC chip out. Tried two spare ones and both result in a black screen. Take it out and self test loads. Tried with holding option too.  This board has been nearly a year off and on to get working so any ideas to finish would be wonderful! Thank you!  

 

 

Process: checked all chips and put in good ones if needed. Even installed a new power switch and SORTED THE COLOR with the NTSC color adjustment knob on the board. WHOOOHOO!  



#2 DrVenkman OFFLINE  

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Posted Sat Jul 15, 2017 8:11 PM

FINALLY got my problem 800xl board running... EXCEPT it only works with the BASIC IC chip out. Tried two spare ones and both result in a black screen. Take it out and self test loads. Tried with holding option too.  This board has been nearly a year off and on to get working so any ideas to finish would be wonderful! Thank you!  

 

 

Process: checked all chips and put in good ones if needed. Even installed a new power switch and SORTED THE COLOR with the NTSC color adjustment knob on the board. WHOOOHOO!  

 

Dumb question but it's worth asking: are you sure you're inserting the BASIC chips oriented correctly? It's unlikely all three of them are bad. Another (more likely) possibility: is the socket for the BASIC chip bad? Look at it closely under magnification with a bright light with the chip removed and see if any of the wipes are bent and no longer flexing out properly. Are any of the wipes broken or heavily corroded? After that, watch closely as it you put in the chip: are all the legs of the chip are making good contact with the socket wipes? 

 

I bring this up because one of my 1200XL's had THREE (3!) bad sockets that had to be replaced before the machine would run. 



#3 seastalker OFFLINE  

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Posted Sat Jul 15, 2017 8:41 PM

Very good idea!  I may swap it out all the same if ram testing fails. I'm swapping out ram chips. I heard one YT video repair say if it goes right to self test it is probably a bad ram chip(s). Wish I had a working board to test as process of elimination would be easier. :)



#4 Rybags OFFLINE  

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Posted Sat Jul 15, 2017 8:52 PM

Can you transfer downloaded programs to load on the real Atari?  Or use another Atari in Basic to run a program to write a disk file?

 

A quick and dirty program could be used to display the Basic Rom onscreen which could tell you if the Rom is being read properly.



#5 seastalker OFFLINE  

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Posted Sat Jul 15, 2017 9:22 PM

Using RespeQT I was able to load Frogger and Football, but not Forbidden Forrest. This only works if I do NOT hold option like normally required, AND I must remove any Basic IC. With it installed, the 800xl boots and freezes at the normal blue screen but no sound nor "ready" prompt.  If I hold option before booting it goes to black.

 

Does this sound like a socket issue or is the no need for holding option plus it wanting to boot the self test more indicative of ram issues? I'm going to look for a ram test program that can pinpoint WHICH ICs are problematic.  Thanks so far to everyone- I feel so close to the finish line... :)

 

 

EDIT: Self Test memory only shows 40 consecutive memory green squares. Hmmm... if 8 (kb?)  are bad that means at least two chips fail... thinking 8 chips = 6kb per chip?  Going to start swapping and retetsing    


Edited by seastalker, Sat Jul 15, 2017 9:52 PM.


#6 Rybags OFFLINE  

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Posted Sat Jul 15, 2017 10:18 PM

Try this executable.

First boot Dos with Basic Rom in the socket, holding Option to disable Basic.

 

Then Binary Load the program BASICON.XEX.  It will change the screen origin so that it's showing the contents of the end of the Rom.

 

Screenshot for reference, this is what you should get onscreen.

 

Attached File  BASICON.XEX   81bytes   8 downloads

 

Basic Rom screenshot.png

 



#7 seastalker OFFLINE  

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Posted Sat Jul 15, 2017 10:44 PM

Again, I can't load when basic is present, but I did try again with DOS.  Best I could do was use the respecQT program to boot an executable and I pointed to your file and got a screen with some of the characters blinking. What does this program do or let us now know? Thanks.



#8 Rybags OFFLINE  

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Posted Sat Jul 15, 2017 11:29 PM

It should be loaded with Basic present but disabled, ie hold Option when booting.

 

It sets up a screen display with the Basic Rom enabled, showing most of the last 1K of the Rom area.  If the machine works properly then it should look exactly as shown.



#9 walter_J64bit OFFLINE  

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Posted Sun Jul 16, 2017 4:15 AM

Is it a bad thing? Just get your hands on a Basic cart and just run your 800Xl as is!  :music: 



#10 seastalker OFFLINE  

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Posted Sun Jul 16, 2017 5:52 AM

looking into a basic cart now... always good to have as a backup. Will experiment more with the attachment too. Seems I at LEAST have a ram issue to address. If I cant work it out I suppose one of the available memory upgrades would be better than replacement chips.



#11 Rybags OFFLINE  

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Posted Sun Jul 16, 2017 6:44 AM

Self Test result is as expected.  It will only check a maximum of 48K of the 64 installed.  If Basic is present it'll only check 40K.

 

8 Ram chips each supply a single bit for any possible address.  My suspicion is your Ram is fine, the Basic problem is probably the socket, MMU, PIA or physical connection going to the socket.



#12 DrVenkman OFFLINE  

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Posted Sun Jul 16, 2017 7:19 AM

If the BASIC socket itself is fine, PIA and MMU would be my next suggestion as well.

 

I'll note that in the case of two of the bad sockets in the 1200XL referred to above, the only way to know the socket wipes weren't making contact was to press against the side of the pin with a logic probe - By checking each pin with the proble, I could see when a pin wasn't getting a signal and, by pressing firmly against the side of the pin, force it to make contact and suddenly start getting a proper signal. That was my cue to replace the faulty socket(s). 



#13 seastalker OFFLINE  

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Posted Sun Jul 16, 2017 8:00 AM

@Rybags: Was able to run your program with chip installed now and got your screenshot but with MANY characters flickering rapidly and (from the left side of screen) the whole 2nd vertical row was blank. Screenshot can be taken if helpful. Swapped PIA and problem persists. So I am on to re-socketing next - couldn't hurt.



#14 DrVenkman OFFLINE  

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Posted Sun Jul 16, 2017 8:02 AM

Swapped PIA and problem persists. So I am on to re-socketing next - couldn't hurt.

 

Have you swapped the MMU?  Resocketing isn't a quick job and there's always a risk of damaging a solder pad or lifting a trace. 



#15 seastalker OFFLINE  

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Posted Sun Jul 16, 2017 8:20 AM

The CPU and MMU do run a bit warm.  Unfortunately I don't have a replacement MMU to test with. Going thru spare chips now..



#16 DrVenkman OFFLINE  

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Posted Sun Jul 16, 2017 8:31 AM

CPU and MMU do run warm normally so that's not necessarily an indicator of issues.



#17 Rybags OFFLINE  

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Posted Sun Jul 16, 2017 8:39 AM

A screenshot would be helpful - or a video given that there's flashing and changing characters.



#18 R.Cade ONLINE  

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Posted Sun Jul 16, 2017 9:06 AM

Is it a bad thing? Just get your hands on a Basic cart and just run your 800Xl as is!  :music:

 

I tried to run my 800xl with a BASIC cartridge and it doesn't work properly. I had a bad BASIC ROM that I removed. Eventually I had to just replace it with a rewired EPROM.

 

It seems to work, you can get to READY prompt and all from cold boot, but a lot of things break or act funny...



#19 seastalker OFFLINE  

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Posted Sun Jul 16, 2017 10:33 AM

ATTACHED: first test with  Rev C Basic chip.  Characters were flickering and second vertical row missing.  2nd one is a video afterwards where I swapped the socket out and put in a different one (Rev a or B likely).  Does this tell us more?

Attached Thumbnails

  • Rev C - Copy.jpg

Attached Files



#20 Rybags OFFLINE  

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Posted Sun Jul 16, 2017 9:35 PM

That's definite weirdness.   And checking a couple of flickering values it's not like just a bit or 2 is alternating.

Got multimeter?  Maybe check the voltage that the Rom is getting, compare it to the OS slot.



#21 1050 ONLINE  

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Posted Mon Jul 17, 2017 12:05 AM

Whenever I run into random screen characters I seem to be
able to help that situation a great deal by changing out
U18, a 74LS08 for a 74HCT08 with a bit more punch for the
system clock. I was ready to blame the MMU until the
screen characters changing came up.

ANY other 74LS08 would do for a test replacement if you
have one on hand too. I just happen to have a stick of
the better ones at the ready.

#22 seastalker OFFLINE  

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Posted Mon Jul 17, 2017 11:39 AM

just tried the swap and still not fixed.  Thanks for the new idea.  I may need to pass this project to someone with a scope



#23 DrVenkman OFFLINE  

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Posted Mon Jul 17, 2017 3:31 PM

Checking the BASIC rom chip pins with a logic probe (under $20 from Amazon) will let you see if the pins that are supposed to be getting signals are actually getting them - that the right pins are steady high, the right ones are steady low, the proper ones are pulsing with signals on the bus ... Not nearly as sophisticated as an oscilloscope but a lot less cheaper and very useful. 



#24 1050 ONLINE  

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Posted Mon Jul 17, 2017 5:20 PM

"Someone with a scope" may or may not be able to whittle
this one down to a fix either. Depends on the guy at
the controls to a large degree plus his equipment.

$40 would get you a universal USB device programmer
with which you can produce your own MMU in GAL form.
I've done this and they do work with only minor issues
from time to time. You still have options to test, I
would only relegate it to the shelf after exhausting a
real 74HCT08 and verified working good MMU swap.

But I will also be getting the DrVenkman tool for my
own toolbox too. It's simply about time I had a decent
logic probe as they are handy for other work as well.




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