Atari 800xl with Black Screen

[poorcomputerman]

The unit had a black screen but now it has a red screen after I swapped out the GTIA. I also swapped out the memory, the Antic, and the Cpu. I am guessing now that it could be the MMU. Any ideas?

[Geister]

Parts swapping can only get you so far and may result in more dead parts. Have you at least checked the basics? You have power, but is it within safe limits?

Do any of the chips seem extremely hot?

Do you own a logic probe or know how to use one?

Do you have a schematic?

Don't guess, test!

[Guest]

red screen checks:

■ Leave system running and check if any chips get hot - REPLACE ANYTHING HOT. Nothing getting hot? proceed to next step
■ Look at swapping in/out Basic Rom with known good part.
■ If no change, then next try; CPU, MMU, OS Rom and Ram chips
■ The fact that you have a red screen means that GTIA is (at least) working at a very fundamental level) - but can still be faulty. Replace.
■ Is your display steady or does it flip/roll? If steady, then again Antic is managing to issue VSYNC commands - but may still be faulty. Replace.
■ Finally, 800XL Field Service Manual states a reddish/brown display may be U2-U5, 18, 19, 28, 30. Replace these.

 

also some "black screen" checks are worth exploring:

■power up using OPTION key, wait five seconds, press SELECT key once, press START

do you hear the musical notes? if so your computer is working
now press HELP, then SELECT, the START
press different keys randomly....do you hear the keyboard BEEPS?
these are good signs that atari is fundamentally ok.
■ power supply may be a problem - it may not be supplying 5v. try another PSU.
■ RF or monitor output? if RF, does machine have a channel switch next to the RF output socket? try repeatedly moving it back and forth - it can get dirt inside and cause bad contact. try a monitor cable - these are fairly standard these days and usually come in the form of monitor to scart, monitor to S-video and monitor to RCA varieties.
■ try booting with a cartridge in the slot -
Star Raiders cart runs a diag on Antic, CPU and GTIA - so if Star Raiders works then ALL three should be good
which narrows your fault down to PIA, OS Rom, MMU or Ram

 

good luck

Edited March 25, 2018 by Guest

[+Nezgar]

Red screen often means bad OS ROM, I didn't see that in your list of chips swapped so far.

 

Brenski's got a pretty comprehensive list there though.

Edited March 25, 2018 by Nezgar

[poorcomputerman]

I am using a modern aftermarket power supply to avoid overcurrent damage. None of the chips are hot. You can see the red screen change a little when I press reset, but the self-test does not seem to function blindly.

Edited March 25, 2018 by poorcomputerman

[Guest]

have you tried a Star Raiders cart?

if not, do it - it definitely eliminates 3 "possibles"

 

have you tried any of the black screen options i suggested?

especially the "blind keyboard test" i suggested - powerup using OPTION then SELECT and START

it's important, because you started with a black screen, before "going red"

give 'em a go and report back

Edited March 25, 2018 by Guest

[flashjazzcat]

Star Raiders cart runs a diag on Antic, CPU and GTIA - so if Star Raiders works then ALL three should be good.

Star Raiders is a "diagnostic cart", but all this means (to the best of my knowledge) is that it has bit 7 of the cartridge option byte at $BFFD set. This signifies that the cart should be run before the OS is fully initialised. The OS ROM still has to operate well enough to jump through $BFFE, and if the CPU manages to get this far then it's working anyway.

[poorcomputerman]

I tried the blind keyboard tests and nothing happened. I could not hear sounds from what would have been sound test. When going from black to red a also changed the antic, cpu and Gtia for new chips from Best.

Edited March 25, 2018 by poorcomputerman

[Guest]

Star Raiders is a "diagnostic cart", but all this means (to the best of my knowledge) is that it has bit 7 of the cartridge option byte at $BFFD set. This signifies that the cart should be run before the OS is fully initialised. The OS ROM still has to operate well enough to jump through $BFFE, and if the CPU manages to get this far then it's working anyway.

thanks Jon.

i didn't realise that Star Raiders also performed a basic diag on the OS also - but i can see that makes sense.

i'll update my black screen thread @ AS.

[Guest]

I tried the blind keyboard tests and nothing happened. I could not hear sounds from what would have been sound test. When going from black to red a also changed the antic, cpu and Gtia for new chips from Best.

Star Raiders test?

[poorcomputerman]

I need to buy that as I do not have it.

[flashjazzcat]

thanks Jon.

i didn't realise that Star Raiders also performed a basic diag on the OS also - but i can see that makes sense.

i'll update my black screen thread @ AS.

Perhaps you misunderstand. The Star Raiders cart performs no diagnostics whatsoever. It simply runs before full OS initialisation is complete, as do all carts which have the diagnostic bit set. This does not imply any explicit diagnostic functionality on the cart itself, although a cart with such functionality would probably have the diagnostic bit set. Not many game or application carts run as diagnostic carts, but those that do might exhibit slightly different (and perhaps illuminating) behaviour on a broken machine.

[manterola]

I got my 600xl with black screen for a couple of days and finally I find out it was a bad 4464 memory chip.

So you might try new ram

[flashjazzcat]

He said he already swapped the RAM, otherwise it would have been the obvious culprit.

[poorcomputerman]

Ordered Star Raiders so shoukd be able to test soon.

[poorcomputerman]

Just tried Star Raiders. Black screen with original Gtia and red screen with new one from best. Behaves exactly the samw with or without cart. So far replaced memory, antic, gtia, and cpu.

Edited March 30, 2018 by poorcomputerman

[Guest]

Just tried Star Raiders. Black screen with original Gtia and red screen with new one from best. Behaves exactly the samw with or without cart. So far replaced memory, antic, gtia, and cpu.

PIA, OS Rom, MMU or Ram

[flashjazzcat]

He's already swapped the RAM (post 1: memory = RAM), so unless he swapped it for more bad RAM, hopefully RAM can finally be eliminated.

[Guest]

He's already swapped the RAM (post 1: memory = RAM), so unless he swapped it for more bad RAM, hopefully RAM can finally be eliminated.

sorry Jon. having read that the what had been a replaced, I did a cutnpaste from my reply #3 and forgot to remove "or ram"

[poorcomputerman]

It was the rom. It now works great. Thanks for your help.