Green screen with vertical lines down the left half of it

[CommodoreDecker]

Hi!  I bought an 800XL off of an auction site, which said the unit's power light came on but was otherwise not tested because they didn't have the output cables.  The chassis is in good enough condition (and it'll be my first attempt to retrobrite) and even worst case scenario, not all parts would be bad, and the price was low enough.

 

Not terribly surprisingly, it boots up to a solid green screen but with bands of vertical off-green stripes gown down across precisely 50% of the screen, uniformly spaced, and only on the left side. From the midpoint to the right side, the screen is solid green.  

 

The PSU I'm using is in good working order (5.07V, for now... I am ordering USB cables with 1.5Amp AC power packs so I don't worry about the current power bricks going bad anymore...)

 

My first thought upon seeing the green screen o' doom was "must be memory, that's the same green hue when a RAM test initiates". I opened up the case and found two RAM chips that were two pins short on each side. Not sure who the actual owner was but somewhere in this unit's life at least two 16-pin RAM chips were replaced with 14-pin timer circuits.  

 

I purchased the same model number RAM that was shown on the other six chips. These two replacement chips arrived. After swapping and powering back on, the same green screen with vertical bars exists. 

 

All chips I seated down, by pressing on them - not by removing then reinserting.

 

The system board itself is otherwise in excellent shape and all the main chip ID#s match up to the 6502, ANTIC, and so on so only the RAM was swapped out at one point. I didn't look at the smaller chips directly behind the cartridge slot but I am doubtful any of those would have been swapped with those mismatched pin count timer chips.

 

At this point, I'm thinking either fully reseat all the chips, perhaps order six more RAM chips of the same ID#, or think about which chip(s) control the RAM as, due to the incorrect chips shoved into the two RAM sockets, it's not beyond imagination that other RAM chips and/or a controller may have been fried as a result of the former owner's tomfoolery.

 

I do have another spare 800XL, which works except for the keyboard so I might swap keyboards and keep the other motherboard as oversized storage for the remaining chips. But, depending on how many chips directly access the RAM (the MMU? PIA? Others? This 800XL does not have a Freddie in it...), it might be worth finding a replacement chip and swapping it out.  

 

If I start random chip purchasing, which is likely, does anybody sell them individually?

 

Thanks much!

 

(Pictures available upon request)

[+Nezgar]

5 hours ago, CommodoreDecker said:

The PSU I'm using is in good working order (5.07V, for now... I am ordering USB cables with 1.5Amp AC power packs so I don't worry about the current power bricks going bad anymore...)

Most Atari 5V PSU's are reliable and can be trusted - except one - we call it the "Ingot" See this post. Otherwise, a modern 5V switching PSU is not a bad thing to use once fitted with a compatible power connector.

5.07V is well within tolerance of 4.7 to 5.2V.

 

5 hours ago, CommodoreDecker said:

I opened up the case and found two RAM chips that were two pins short on each side. Not sure who the actual owner was but somewhere in this unit's life at least two 16-pin RAM chips were replaced with 14-pin timer circuits.

Can you post a picture of them? Could be leftover from something else, like a memory upgrade that was maybe removed.

 

5 hours ago, CommodoreDecker said:

I do have another spare 800XL, which works except for the keyboard

This is great. Yeah you could use the "good" keyboard on the "good" machine so you at least have a 100% machine to compare with. Swapping it will also confirm if the problem is with the keyboard itself, or the computer... Start by swapping the 8 RAM chips from the "bad" machine in to the working machine and see if it works there. If you turn on the computer with OPTION held down, you should get the self test where you can run the simple memory test there.

 

Next swap the OS ROM (CO61598) from the bad machine into the working machine and test.

 

If not continue one at a time with:

 

CO61618 - MMU, CO14806 - CPU, GTIA C014805, ANTIC CO21697, and finally PIA but that's the least likely to cause this issue.

 

The OS ROM and MMU can be programmed to an EPROM or GAL if a new one is needed by people here on the forum for you.

 

You should be able to narrow it down to the specific IC this way. It's advisable not to go the other way by putting IC's from the good machine into the bad so you don't wreck them

 

Good luck, curious to hear the results of your tests.

[Rybags]

What happens when you press Reset?  If you get an audio click, that means the OS is probably OK.

[Sugarland]

8 hours ago, CommodoreDecker said:

Hi!  I bought an 800XL off of an auction site, which said the unit's power light came on but was otherwise not tested because they didn't have the output cables.  The chassis is in good enough condition (and it'll be my first attempt to retrobrite) and even worst case scenario, not all parts would be bad, and the price was low enough.

 

Not terribly surprisingly, it boots up to a solid green screen but with bands of vertical off-green stripes gown down across precisely 50% of the screen, uniformly spaced, and only on the left side. From the midpoint to the right side, the screen is solid green.  

 

The PSU I'm using is in good working order (5.07V, for now... I am ordering USB cables with 1.5Amp AC power packs so I don't worry about the current power bricks going bad anymore...)

 

My first thought upon seeing the green screen o' doom was "must be memory, that's the same green hue when a RAM test initiates". I opened up the case and found two RAM chips that were two pins short on each side. Not sure who the actual owner was but somewhere in this unit's life at least two 16-pin RAM chips were replaced with 14-pin timer circuits.  

 

I purchased the same model number RAM that was shown on the other six chips. These two replacement chips arrived. After swapping and powering back on, the same green screen with vertical bars exists. 

  

All chips I seated down, by pressing on them - not by removing then reinserting.

 

The system board itself is otherwise in excellent shape and all the main chip ID#s match up to the 6502, ANTIC, and so on so only the RAM was swapped out at one point. I didn't look at the smaller chips directly behind the cartridge slot but I am doubtful any of those would have been swapped with those mismatched pin count timer chips.

 

At this point, I'm thinking either fully reseat all the chips, perhaps order six more RAM chips of the same ID#, or think about which chip(s) control the RAM as, due to the incorrect chips shoved into the two RAM sockets, it's not beyond imagination that other RAM chips and/or a controller may have been fried as a result of the former owner's tomfoolery.

 

I do have another spare 800XL, which works except for the keyboard so I might swap keyboards and keep the other motherboard as oversized storage for the remaining chips. But, depending on how many chips directly access the RAM (the MMU? PIA? Others? This 800XL does not have a Freddie in it...), it might be worth finding a replacement chip and swapping it out.  

 

If I start random chip purchasing, which is likely, does anybody sell them individually?

  

Thanks much! 

  

(Pictures available upon request) 

 

Any 5v DC XL/XE psu's can go bad, but the ones with the XL styled case (black or white) are serviceable.

 

Since you have a fully working 800XL one approach is to swap chips from the known working into the non-working machine.  Yes first do all the RAM chips at once, then if you rule that out, swap the custom/primary chips one at a time. Use a chip puller. A screw driver that will bend the legs.  Good primary candidates for the symptom you are seeing is GTIA, CPU and Antic (in that order).   First fully inspect the bad motherboard to be sure it has no physical faults like a dry solder joint or burned area or blown cap. Otherwise some deoxit and cleaning of the chip legs may help. You can check the chips from the non-working in the known working as well to rule them out.

 

 

 

 

Edited October 21, 2019 by Sugarland

[+DrVenkman]

42 minutes ago, Sugarland said:

Since you have a fully working 800XL one approach is to swap chips from the known working into the non-working machine

Chip-swapping is a tried and true method of empirical troubleshooting, but please do the reverse. That is, swap chips FROM the non-working machine INTO the working machine, one at a time. That will both identify any bad components as well as ensure that if whatever killed the machine is endemic to the board (such as a hidden dead short somewhere) won’t take down both machines by killing previously known-good chips.

[CommodoreDecker]

Thanks!

 

There were no dry solder connections or popped capacitors.

 

I'll start swapping chips from the BAD machine to the good one -- excellent point on not wanting to fry any known working chips, especially as the chips used to replace RAM were timer chips and those probably did cause damage when the former owner swapped them. I'm thinking ANTIC and/or GTIA being the fried chip(s) - assuming the RAM I put in isn't hosed, but it might be another.

 

I doubt I'll have 2 complete sets of operable hardware but whatever works on the good one is still a bonus as I've moved the keyboard and will retrobite the case shortly...

 

Thanks again!