800XL Black Sceen Fault - Help Needed

[EvilDoctorShortCrust]

Hey folks,

 

Ok so I posted a while ago about an 800XL which had a sound fault. At the moment I'm no further on with finding the cure so have moved on to this other I have which only displays a black screen. I have tested these chips in a working board; Sally, Antic, GTIA (+ Pokey & OP-Amp whilst trying to cure sound issues) but all of these are good chips. None of the other chips in these boards are socketed so.... before I start going crazy desoldering chips can anyone give me some pointers towards the most likely culprits?

 

All advice glady received

[mimo]

Please search the forums for any of the hundreds of other "my xl is not working" threads.

[Macc]

And an actually helpful reply reads

 

try here

[flashjazzcat]

Absolutely: why tell someone to go use the search facility when they could have simply scanned the topic titles on page one of the forum and found said topic a few entries from the bottom.

[atari8warez]

What a waste of forum space.... why bother answering if nobody is willing to provide a useful answer, I am sure he would have thought about searching the forums if he didn't get an answer to his question, besides sometimes pointing a noob to the right thread proves more self satisfactory than just making a mockery of him...

[EvilDoctorShortCrust]

Ok, I've tried really hard not to rise to the bait here but I'm finding it hard to hold back much longer and thanks to those how have spoke out favorably towards me.

I had actually searched a number of posts and seen a considerable amount of waffle amoungst the content. What I had actually asked for, which I could not gleen from other posts, was the most probable causes so I didn't have to go round like a dog chasing its own tail. Oddly enough I thought this was a forum where people helped each other out in order to keep these systems alive and enthusiasm running strong. Clearly it appears to be just another social networking site where people either bitch or engage in self-congratulation generally saying alot whilst saying nothing at all.

I don't want to fall out with anyone and I probably should of made my position clearer as to where I was up to and what i had researched, so my bad on that score.

As you'll see from my profile I am a relative newbie to the forum but I do understand this - You need to keep it real fellas and if you want to chat socially then do it where it is appropriate or newcomers like myself will be turning away in droves

[atari8warez]

I had actually searched a number of posts and seen a considerable amount of waffle amoungst the content.

 

I am with the board since 2007 and still overwhelmed with the amount of info available through the forums. The search engine here isn't one of the best (no offense to the board operators, but it's the truth) and a search for "Atari 800XL black screen at boot" would return tons of results with only a handful really being useful.

 

In any case, if you get a black screen at boot, given that you verified your power supply is good, I would suggest opening up the case and do a visual check first. Connect your power supply and turn it ON after opening the case, then after a few minutes touch the 6502 CPU and feel if its warm (if it is then the power is being supplied to the board), if it's not then touch other chips and see if any is getting warm. If they do the CPU MIGHT be bad. Turn the computer off and do a visual check to see if you can locate any burn outs or bad traces on the motherboard, next check the electrolytic capacitor(s) near the power switch and look for leaks or burst capacitors, If your motherboard is socketed, you may try re-seating all the chips and try powering ON again. If the screen is still black check for SIO sounds coming from the monitor's speakers. Listen for the noise you hear when you turn the computer on without a disk drive attached to it. If you hear the sound but nothing on your screen then it's probably the video circuitry or the RF modulator (if connected to a TV) at fault.

 

It is difficult to diagnose a computer without the proper tools but these are the basic checks you can do yourself. If after all that you still cant be sure what the problem is you probably better off asking for professional help or get a new 800XL if you don't want to bother.

Edited January 27, 2013 by atari8warez

[+David_P]

I'm on another forum that also has limited search functionality. I find that using Google works well for searches.

 

Try "site:www.atariage.com/forums search terms" in Google, then add or remove terms to narrow it down.

[mimo]

Ok, I've tried really hard not to rise to the bait here but I'm finding it hard to hold back much longer and thanks to those how have spoke out favorably towards me.

I had actually searched a number of posts and seen a considerable amount of waffle amoungst the content. What I had actually asked for, which I could not gleen from other posts, was the most probable causes so I didn't have to go round like a dog chasing its own tail. Oddly enough I thought this was a forum where people helped each other out in order to keep these systems alive and enthusiasm running strong. Clearly it appears to be just another social networking site where people either bitch or engage in self-congratulation generally saying alot whilst saying nothing at all.

I don't want to fall out with anyone and I probably should of made my position clearer as to where I was up to and what i had researched, so my bad on that score.

As you'll see from my profile I am a relative newbie to the forum but I do understand this - You need to keep it real fellas and if you want to chat socially then do it where it is appropriate or newcomers like myself will be turning away in droves

 

OK, well I am sorry if I offended you, but it gets tiresome seeing the same questions asked time and time again, especially the same question 3 times in a week.

As for helping, well I go out of my way to help people on these forums, which is well documented.

As for saying a lot but saying nothing, well that's your take on things.

[flashjazzcat]

A new user's reaction to being asked to use the search facility can sometimes be as revealing as he considers forum members' reactions to his initial question to be.

[Frankie]

A new user's reaction to being asked to use the search facility can sometimes be as revealing as he considers forum members' reactions to his initial question to be.

 

Sun Tzu?

[+bob1200xl]

As to the Reported Problem, (I have a hard time finding anything by searching the forums, too) the Atari powers on with the video in a random state. You usually see some dark, unsynced color. Very early in the boot process, the system writes $00 to all the hardware chip addresses and the screen goes totally blank.

 

So, if your screen goes from 'nasty' to blank, it tells you that the CPU and OSROM work together OK and the hardware ICs can be accessed to some extent. If it stays 'nasty', then the CPU and/or the ROM don't work. (could be MMU, or a whole bunch of other stuff)

 

The next step in the boot process is to find the memory size and zero out most of it. If memory fails, you should fall into the diagnostic screen, which isn't happening. You probably have some sort of memory issue. Check for warm memory chips?

 

Knowing what is happening doesn't tell you why, I'm afraid.

 

Bob

[EvilDoctorShortCrust]

Cheers to Bob & Atarti8warez,

I can confirm the PSU is definately good. I have other working systems with which to test it. The board is visually giving nothing away. Oddly I don't really sense the heat on chips like most folk cos I used to work in kitchens and ended up with so many burns I kinda developed desensitised hands. I suppose I could use the back of my hand or wrist though.

I have actually already swapped a few of the chips you mention into a socketed working board and those I have tried so far all work. I was going to start on the memory next at any rate but it's nice to know I'm travelling the right way around it. Shame both boards aren't socketed but then that'd just be to easy wouldn't it!

Does all the memory affect the initial boot. I don't know if I read something or just simply imagined it but I have a feeling the initial boot only involves a section of memory. Is this correct? For all I can remember this info might have been for an entirely different system in my collection. However if this is the case which chip locations would I be best to start with?

Struggling a bit for time at the moment so it'll be tomorrow night, hopefully, before i get time to sit down with the soldering iron, but I'll report back and let you know how I've got on

Thanks again

[EvilDoctorShortCrust]

On another topic, and I don't know if I should be posting this here or on a new thread, does anyone know of a good head alignment program for Atari tape decks. Interceptor did an Azimuth program for most systems but I've never seen it for the Atari.

I know some of you will say "what do you need a program for - all you need is a good ear". Problem is my ears are very bad and I've never been able to tune them up by ear.

I've also seen homebrew programs on disc for the C64 and I've even seen it on an interface for the Spectrum so I'd really love it if someone could help me find something for the Atari.

The only things I've seen by searching is a post which said to strip down an I/O cable and adjust so that a particular voltage could be read. This seems a bit extreme to me to be honest.

[atari8warez]

Cheers to Bob & Atarti8warez,

I can confirm the PSU is definately good. I have other working systems with which to test it. The board is visually giving nothing away. Oddly I don't really sense the heat on chips like most folk cos I used to work in kitchens and ended up with so many burns I kinda developed desensitised hands.

 

Use your lips... .... really... I am not joking, they are much more sensitive then your fingertips... I actually kissed my XEGS today, testing for a bad ROM. The self-check screen shows a ROM error and indeed the OS ROM was the only one that gave me a cool kiss.....Just make sure the computer is turned off before expressing your love though ....

[atari8warez]

Does all the memory affect the initial boot. I don't know if I read something or just simply imagined it but I have a feeling the initial boot only involves a section of memory. Is this correct?

 

On a 800XL when a RAM chip is bad the machine will jump to the self-test screen (given everything else works properly). So the answer is yes, at least the first 48K of memory will affect it. When the machine boots with BASIC enabled (default state) the RAM under the BASIC ROM is disabled, so is the RAM under the OS ROM. I am not sure whether the computer checks and detects a bad RAM under the BASIC and OS ROMS during the boot.

 

On a 130XE, if any of the RAM in extended 64K is bad, it won't be detected by the computer on boot, it won't even be detected during self-test because 130XE self-test routine only checks the first 64K, so on a 130XE a bad RAM in the extended memory won't affect the boot process.

 

Good luck with the diagnostics....

Edited January 30, 2013 by atari8warez

[EvilDoctorShortCrust]

Ok, so I've really not had time to look at this again till now and just plugged it in again 20 mins or so ago. As I said I struggle to get a good gauge of warmth from chips. The big boys are definately warm and a few of the smaller chips around the board. U locations 9-16 which I assume is memory doesn't really seem to get any chill off them.

One thing which has developed which has not happened since I got this unit is sound. Originally there was no picture or sound of any kind and now there is a constant tone when powered up. Does this alter anything in the diagnosis?