Atari 130xe video issue

[andrew@meler.us]

I purchased Atari 130xe - it powers up but has a video issue - basic screen flickers, self test runs but screen has lots of odd characters.

Any idea which chip to start with?

Sound works fine. Power supply is NOT an issue, as I have 2 - both of them work on my 800xl, not on this 130xe

Couple of pics attached.

 

 

Thanks

[Paul Westphal]

Hmmm, looks like the GTIA but could also be ANTIC.

[Paul Westphal]

I wonder what a S.A.L.T. cart would say

Edited November 10, 2017 by Paul Westphal

[andrew@meler.us]

I wonder what a S.A.L.T. cart would say

 

Thanks, I don't have S.A.L.T cart. GTIA on this machine is socketed - so it should be easy to replace. I searched eBay, don't see it there, will look for one at Best electronics.

[Paul Westphal]

He has a minimum order of $20. I suggest getting a new joystick PCB ($7.95) added to the order. GTIA's are $15, I believe.

[Paul Westphal]

FYI - ANY sockets on a 65xe or 130xe are very rare! You are lucky

[andrew@meler.us]

FYI - ANY sockets on a 65xe or 130xe are very rare! You are lucky

 

This machine would be pristine - if it worked. But GTIA is definitely socketed. Thanks for your help.

[+Nezgar]

Couldn't that also be bad RAM in the area of the display?

 

Probably a good use case for sys-check II

Edited November 10, 2017 by Nezgar

[+DrVenkman]

Couldn't that also be bad RAM in the area of the display?

Could be but probably not. I’ve had three bad GTIA chips in my personal collection - two XL computers and a 5200. All three had similar symptoms but RAM was fine.

[Level42]

FYI - ANY sockets on a 65xe or 130xe are very rare! You are lucky

Not so rare, there were lots of bad GTIA,s in that era, although this looks like an early 130XE and the bad GTIA's only surfaced with the 65XE/800XE.

 

What IS really rare is the socketed MMU that no-one seems to notice.....I would first of all re-seat that......and the GTIA after it....

 

 

My money is on the two full banks of mT RAMs though.... if you're lucky it's only 1 or 2 or 3....

 

You can try piggy banking a good RAM on each mT one by one and power up....

Edited November 10, 2017 by Level42

[Level42]

Could be but probably not. I’ve had three bad GTIA chips in my personal collection - two XL computers and a 5200. All three had similar symptoms but RAM was fine.

But XL,s almost never had mT RAM,

 

Not sure about 5200s but I don't think they had mT either...

[_The Doctor__]

also cut the two caps near the sio connector c 304 c 303, you sio devices will love you for it.

 

there appears to be a modification above the Atari pcb inlay next to the keyboard post and silk screen... I don't have that on mine.

 

so do the re-seating touch up bad joints with leaded solder, and start the ram checking....no doubt it'll come back to life...

Edited November 10, 2017 by _The Doctor__

[andrew@meler.us]

also cut the two caps near the sio connector c 304 c 303, you sio devices will love you for it.

 

there appears to be a modification above the Atari pcb inlay next to the keyboard post and silk screen... I don't have that on mine.

 

so do the re-seating touch up bad joints with leaded solder, and start the ram checking....no doubt it'll come back to life...

 

 

Thanks for all the replies. I ordered a GTIA chip from eBay, hopefully this will be the culprit.

If it was RAM - wouldn't the computer go to self-test (RAM test)?

I can actually get to the READY prompt / Basic - and start typing - video is distorted (as shown in my first picture).

 

I did reseat the MMU and GTIA - no change in behavior.

[_The Doctor__]

if you get to the ready prompt type BYE or B. and press the return key

do you get the test menus? try each one at a time

[1050]

Screenshot #2 shows self test in music mode so BTDT.

 

I've seen such garbage characters corrected by dropping

in a HCT08 for the standard 74LS08 at U18. This tells

me that it's something to do with timing and/or not so

square edges on system clock signals. Ram is of course

also involved but the root issue is the system timing

is tad bit off by perhaps a weak LS08 chip. One could

piggyback one onto U18 if it weren't for the useless

factory mod involving the pink and purple wires getting

in the way there. Just as a temporary test of course,

good results would dictate a proper entire replacement

then.

 

You could even remove the factory patch pink and purple

wires by restoring a cut trace on the bottom side of the

board and tossing these famous wires in the bin. It won't

make a hill of beans difference either way. It's GTIA's

chip select signal from the MMU IIRC.

 

I've never had to put one back whenever I've taken the time

to remove that factory patch. Highly suspect that management

made this fix up just to keep the repair team busy with

work stacked to the ceiling instead of letting them sit

around reading novels and having food fights.

[_The Doctor__]

I wanted to see the different self test screens not just the one...

changing the 74ls08... why not do it while your waiting for your chip to arrive it will eliminate one more possibility...

Edited November 12, 2017 by _The Doctor__

[andrew@meler.us]

Screenshot #2 shows self test in music mode so BTDT.

 

I've seen such garbage characters corrected by dropping

in a HCT08 for the standard 74LS08 at U18. This tells

me that it's something to do with timing and/or not so

square edges on system clock signals. Ram is of course

also involved but the root issue is the system timing

is tad bit off by perhaps a weak LS08 chip. One could

piggyback one onto U18 if it weren't for the useless

factory mod involving the pink and purple wires getting

in the way there. Just as a temporary test of course,

good results would dictate a proper entire replacement

then.

 

You could even remove the factory patch pink and purple

wires by restoring a cut trace on the bottom side of the

board and tossing these famous wires in the bin. It won't

make a hill of beans difference either way. It's GTIA's

chip select signal from the MMU IIRC.

 

I've never had to put one back whenever I've taken the time

to remove that factory patch. Highly suspect that management

made this fix up just to keep the repair team busy with

work stacked to the ceiling instead of letting them sit

around reading novels and having food fights.

 

The GTIA chips is not the issue - got a replacement one and the 130xe has the same behavior.

I'll look over the other suggestions this weekend. I might just put it on ebay - too bad as the case and keyboard is pristine...