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Atari 800 XL black screen


alortegac
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Hi guys! Me again. Well, I have bad news, now X2. I bought another 800xl computer with powersupply(seller tells me it was working fine ...). But is DOA. The power supply is an ingot and only supplying 4,2v.....so computer does not even power up; Only On/Off led ON but nothing in the screen. Therefore DOA.

 

So, I tested it with my other power supply from coputwr #1. It was boothing with garbled green screen. See picture 1.

So, then I compared both boards by swapping 1 chip at at time from one to the other very carefully. Hoping to find a bad chip causing the issues. Or get 1 board working of the 2.

Nothing. Both boards are now doing exactly the same thing. Solid green screen. See pic 2 is board 1 and picture 3 is board 2. Color can adjusted to red or blue with the potentiometer resistor. No sounds, only solid color. In AV or RF. Same thing.

 

Therefore, I have 3 hypothesis: 1) the bad chip is the same in both. 2) problems with the boards are not related to any chip, maybe a cold solder, my tv or something else. 3) power supply is the problem, even though readings are solid 5V.

Score is 2- 0 loosing! . $130 bet .so far........Should I quit or stay? Thoughts? Comments.....thank you!

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before doing all of that the first thing you do is use a known good power supply... using a power supply from a borked computer to test another computer sounds terrible to me... make sure they aren't commodore supplies, test the supplies unloaded and loaded, should be 5 volts or there abouts both ways, make sure there is no AC hum... which is readily seen on an oscilloscope, better dmm's and crts. Not so much on lcd, plasma displays etc...

 

I honestly hope most people will stop doing this I bought a computer and it wasn't right so I used the power from bad machine routine. It seems to always end in tears...

 

please show us your' power supplies...

 

I wouldn't swap chips like that with a damage computer to a damaged computer... It's best to move them one at a time to a working machine and be quick to power off when you find the failed one.

 

What country are you in and what cable are you using to connect to tv? verify pin out, some tv's have power available on their inputs....

 

we need some good info to help a bit at this point...

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Thanks for your response.

 

1.- Power supply: if you read this thread from the beginning. I did check my computers #1 power supply following the schematics. It appears to be ok with solid 5v+ in all pins not under load, and 5v or under 5v under load in the locations specified in the schematics. I will include a picture. But according to other AA post on this topic, this should be a good power supply.

Now, the second machine came in with an ingot power supply. I was told it was OK. Then when I tested it, found out it was weak @4.3v.

I do not have an oscilloscope, as I said before.

 

2.- As I said before I am in the USA, Massachusetts.

 

3.- No, I just did not just began swapping chips like in crazy town......I am trying to follow a protocol,removing/replacing them very carefully, and I am doing the best I can with what I have.....which was only 1 board and now is 2 bad boards. I have very limited spares, basically a new set of rams, 14806c, GTIA and a couple of the gate ics. I tested computer #1 with logic probe following the Sams document. No useful findings.

 

4.- yes, I agree. This is not an ideal situation for me. I am frustrated because I do not think I have everything necessary available for this project. I do not have a working computer to test with, as you also suggested. I tried by purchasing a second computer, which also did not work! !!! These machines seem to be very touchy, somewhat mediocre quality control from the manufacturer. I have a TI99/A. I had it up and running in 2 days.

 

5.- I hope this clearly explains my problem. BTW, I am not an expert but I am not an idiot with 2 bad computers, as you somewhat suggested it in your editorial comment.

 

Doctor, please help me if you can. I will greatly appreciate it. I am trying to learn about atari 800 xl computers and may make few mistakes along the way.....but not purposely. I have saved from recycling more than 200 hundred classic consoles, atari, intellivision, colecovision and few others. I just never tried on fixing computers before.

 

Thanks a lot!

Edited by alortegac
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Pictures 1 and 4

#1 power supply (good one?)

Picture 2 and 3

# 2 power supply (bad? Only 4.3v)

 

Picture 5 ( monitor)

Picture 6 rf cable

 

Picture 7

Av cable...works fine with my TI99/4A

 

 

I hope you can find if something is wrong. I will try them in a different monitor using RF cable.

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Hi, just a quick update. I tested both boards with a different monitor. No change.

Also, by checking on options for power supplies I came across another thread here in AA. Suggested to use a modern power supply 5v and >1A. So, I created mine. Yes! I checked pin out and all is good. Power supply was 5v+ not under load.

Well, I checked both boards with it. No change. Only slightly different color in one of them. Pictures attached.

 

Thanks a lot!

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Edited by alortegac
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the white brick is re-build-able and a keeper,

the ingot is nothing but an Atari KIller cut the ends off and have at with a 10 lb sledge hammer!

 

The one you bought last that was suppose to work came with what power supply? If it was the ingot... check ram and support chips.. and the main cap near power switch.

 

De oxit is your friend, if chips are socket-ed then deoxit, pull an re insert making sure no legs are out or folded under, while chips are out make certain no wipes are damaged in sockets.

 

make there are no cold solder joint or shorts to shielding, no flakes shorts or bridges under sockets or chips etc.

 

That's just a quick run down, but there are endless threads giving the low down on fixing up these well made machines up.

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Doctor, Yes, ingot is gone. This came with the second machine. Used ends to build the modern ps. Thanks!

 

All other AA members in this thread:

I have pretty much done everything you all suggested. Very careful visual, some multimeter and probing testing.

I do feel my time is not very well spent in checking individual components and circuits with multimeter and sams document. And Without a good machine, there is not much else I can do.

 

Therefore, unlesss any other suggestions, I want to again thank all for your valuable inputs.

I am only waiting to receive a couple of new rom chips. Thanks Nezgar!!! Special thanks to shoestring and Jiroh too. Thanks guys!

 

Ps. no worries I will not send them to the rec. bin.....I will sell them for parts along with all my atari 800xl stuff. Both empty Keyboards/cases, the oem ps that is rebuidable and few game carts. I am not sure about the boards....maybe for parts only.

 

Al

 

Ps2: Serious lack of a tight quality control. Engineering changes were executed poorly, Sockets look pretty cheap, faulty power supply can cause fatal failures and quality of overall components very questionable. No wonder, Atari computers tanked while apple is very well alive.

Edited by alortegac
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I've had Apple ii power supplies burn up, with various quality of component over the years... so I don't know what your' saying... Atari had one truly crappy power supply out of many. Let's not even talk commodore power supplies. The Atari is the easiest to repair IMHO. I've only ever lost one to an ingot in the 1980's, I have never used an ingot since. Just because someone stuck you with one doesn't make the entire line crap. There are far worse computers out there.

 

I think it's going to be ram or it's support chips feeding garbage to the bus

 

Taking a look at your posts, it looks like you've had an amazing run on of bad luck.. colecovision, 7800, 2600, and xl's at first glance. You must have electric death living with you, he kills something once or twice a year. Hopefully you will rescue these last two as you have the others.

Edited by _The Doctor__
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Hi again Doctor,

 

Apologies, I offended Atari's quality control processes. Let us stay on topic, No RAM issue, I checked with fresh set of chips. New ROM is on its way.

 

And Yes, I would come here mostly whenever I cannot figure out something by myself. Asking for support or guidance from experts like yourself. About my luck, I actually think the opposite is true, I have had an excellent run so far. Many, many rescues, very few losses.

 

I am surprised the"experts" have never taken time or put effort in creating a single "STANDARD REPAIR PROCEDURE" Designed for beginners, newbies....non technical people. A robust "expert system" that could help saving these machines from the destruction due to poor execution in the "fixing". AA Posts are all over the place, thousands of them...similar, conflicting information, etc. Every black screen post is a "groundhog day". I would think this machine is simple enough development of a simple Diagnostic tool-document - process is feasible. A learning system with videos, documents, diagrams, step by step....etc.

 

Many people spend so much time creating new mods., expanding functionality and new games for this old machines......But there very few options for an inexpensive professional repair nowadays..... you have to take matters on your own hands.....and disaster is more probable outcome than success in many cases. Many machines lost.

 

Anyway, maybe it is just me thinking out loud.

 

thanks a lot!

Edited by alortegac
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I am surprised the"experts" have never taken time or put effort in creating a single "STANDARD REPAIR PROCEDURE" Designed for beginners, newbies....non technical people.

 

 

That's because we all became "experts" by banging our heads against these kinds of problems using the materials and techniques at hand: Field Service Manuals, SAM'S guides, chip-swapping, multimeters, logic probes and 'scopes, and often on more than one piece of hardware … We're no longer the ones who need a guide, and frankly, most systems can be brought to life with just a few of the usual steps - bad OS ROM, a bad RAM chip, faulty ANTIC or GTIA, whatever … it's not usually that involved of a process, and if it gets to be, you either need to take the time to educate yourself how to use the more technical resources and tools, send it to someone else to fix if you can find one (I know you've suggested that already), or simply put it aside in favor of something else more enjoyable.

 

That said, it's a darn shame you're having so much trouble. As Nezgar points out, one of those systems is trying to come to life. I'm a little concerned that the display is all green - on modern flatscreens, many red-brown colors on CRTs "translate" across the NTSC color space to greenish-golds (see videos any Lucasarts game on a CRT vs. LCD, for instance). So either the system is only putting across reds, or the color pot is all screwed up. But set that issue aside. The important part is that some part(s) of the system are actually working. My guess for that system would be CPU, OS ROM, MMU, PIA and/or a generalized RAM problem, in basically descending order.

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I continue to think MMU and support chips as he says the ram chips are known good and the other large scale chips have been swapped. There are many very good threads and videos made about repairing the Atari that we all have participated in.

 

I use an upside down aero duster to cool chips and see who runs hot, I also use alcohol in a spray bottle... he who dries super fast is often bad.

of course a sys check card is always a plus....

 

Flash Jazz Cat also make youtube videos on mucking about to a repair, he doesn't post the perfect fix every time, he shows the process warts and all and that can be helpful.

 

good lead based solder, soldering iron, solder sucker, dmm and logic probe and spare chips is where you start, with a scrutinizing eye on the pcb and it's components.

 

mmu, support chips and/or Antic is still my bet followed by the CPU in checking order

 

have you tried any cartridges like star raiders etc?

Edited by _The Doctor__
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Thank so much. I will let you know when I find something new. My plan is to test circuit by circuit checking voltages according to sams guide. I will also try checking on the hottest chip. I do have a laser thermometer, very precise.

I am waiting for the new rom from Nezgat too.

 

Thanks guys. And please do not take my comment the wrong way. I do not mind learning or working hard to fix these consoles. I was really thinking about a system for avoiding mistakes that will destroy the computer ( as many of you have probably made one way or the other while learning). At the same time, I was trying to let you know I am not just doing things randomly or carelessly.

 

Also, I have professional electronics equipment. I just do not have an oscilloscope yet, spare parts for this model and another working board.

 

Thanks again for your time,

Al

Edited by alortegac
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While you're waiting for parts... since MMU is still on the suspect list, and you have 2 800XL's, if you haven't already done so, you can try swapping the MMU's. CO61618 (just below to the right of the cartridge port)

 

You can't use the MMU from the 1200XL in the 800XL.

 

I'm not sure where you can get replacement MMU's other than BEST, maybe B&C. Anyone know other sources? I recall some discussion about making them by programming GALs, (But not possible for 130XE eMMU)

 

Can't remember if you said you had replacement sn74ls158n (memory multiplexers) coming? if not, they're cheap & common on ebay too. They are the 2 chips next the the column of 8 DRAMS on the left of the board.

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Ps2: Serious lack of a tight quality control. Engineering changes were executed poorly, Sockets look pretty cheap, faulty power supply can cause fatal failures and quality of overall components very questionable. No wonder, Atari computers tanked while apple is very well alive.

Look in any Apple Iie enhanced, youll find single wipe sockets. The same variety used in other cheaper computers. Apple II power supplies had their fair share of problems too although superior in design, they were encased and lacked ventilation holes and as a result most Apple II power supplies need a rebuild.

 

People seem to forget that Apple almost went out of business in the late 90s. Steve Jobs had just returned to Apple and it was Bill Gates that saved the company from bankruptcy by investing over 100 million dollars

Edited by shoestring
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I'd wonder about CO60302A and CO60472. Those are your BASIC and the XL/XE delay. I don't currently own an 800xl, but do had some 600xl's and use XEGS + 65xe. Those 2 were the most common failures in mine. I also fixed an 800xl for a friend that had a bad Basic. He'd turned it on and only got a blue screen, but no ready prompt. He cycled the power switch to restart and it went to black screen, and greenish screen with OS removed.

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Hi guys,

 

Ok, here is my progress. I checked every single IC in computer #2 with probe and made a map and a matrix of my readings using the sheet from SAMs guide. I also checked temperature on the chips. Being U4 the hottest, running @over 120F all other around 90F.

 

Attached pictures for your review.

 

After reviewing the map. You can see many, many issues, all the big head blue/purple pushpins in the map were PINS with NO reading - Dead pins / 0v. Then I noticed U3 PIN 20 was L not making any contact. It was low. I marked it with RED pushpin in the map. This is the vcc must be High. So, I removed the chip, reposition legs, sprayed some contact cleaner and replaced in position firmly.

 

 

 

I will continue with report on the changes after this fixing U3 issue in another reply to avoid any confusion.

 

 

=======> thanks!

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Edited by alortegac
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=====> Continue -

 

After fixing U3; I rechecked everything again with the probe and multimeter (when in doubt). See pictures.

 

I did not find any more open traces or any more very evident issues. (at least not to my untrained eyes).

 

I noticed the following main patterns:

A7 address - Is still all wrong.

U19 Pin 5 remained No reading at all (dead) with probe but with voltage OK with multimeter......(?). It should be P.

CPU pin 6 is High. (no pulse)

U3 is almost OK, other than pin 17 that connects with U2 Pin 4.

All RAMS now ok 100%

U17 P4 is ok. I think it was an error on my first reading.

U7 NIM bar, U23 CS2bar and U17 SO, SI, S2 bar still wrong.

Video output from GTIA appears to be bad, but I think it is because something else is bad. I check GTIA on a 5200 and worked fine.

U20 4050 is good. New IC

U2 is NEW IC. Should be good. but still problems there. P14 is actually now Ok (I just missed to remove this push pin). Not sure what NC stands for.

 

Ic's running cooler. between 80 and 90 F. U4 still the warmest.

 

Question: I am testing with NO keyboard connected......It is ok?

 

 

I think this is it. ........ Machines is doing still the same. Sometimes some garbled screen and most of the time solid greenish dark screen.

 

 

DO YOU SEE A PATTERN? What can I do next?

 

thank you so much for your assistance.!

 

Al

 

 

 

 

 

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I noticed the following main patterns:

A7 address - Is still all wrong. ***

U19 Pin 5 remained No reading at all (dead) with probe but with voltage OK with multimeter......(?). It should be P.

Wrong it's NC and should not pulse

 

CPU pin 6 is High. (no pulse)

Will only pulse if NMI is issued by running code.

Clue - it's not running code...

Dirt napping CPU.

 

U3 is almost OK, other than pin 17 that connects with U2 Pin 4.

All RAMS now ok 100%

U17 P4 is ok. I think it was an error on my first reading.

U7 NIM bar, U23 CS2bar and U17 SO, SI, S2 bar still wrong.

Have no idea what bar you refer to in last line quoted

above.

 

***

Cool running indicates the CPU isn't working it next

to death because a healthy one will be warm all over.

 

It is OK to test without the keyboard attached.

 

NC is short for No Connection meaning the pin isn't

connected to anything at all.

 

It seems to me that the CPU is dead so it can't

issue NMI since it's not reading code and performing

tasks related to that function. GTIA has very little

work to do as well.

CPU pin 6 is NMI signal to GTIA.

Edited by 1050
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Thanks for your input. Will a 14806 cpu from a atari 5200 work on this machine?

 

My comment on this line:

U7 NIM bar, U23 CS2bar and U17 SO, SI, S2 bar still wrong.

 

The nomeclature in the schematics show them with a bar above the name of the signal, I think it means signal was inverted or flipped. Apologies for my lack of correct naming.

 

Ics are warm around 80-90F....not cold or super hot above 100F. I am going to take another reading with the thermometer.

So, what would you suggest? Does this tell you anything else?

 

Thanks a lot!

Edited by alortegac
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Apologies, I offended Atari's quality control processes. Let us stay on topic, No RAM issue, I checked with fresh set of chips. New ROM is on its way.

 

I am surprised the"experts" have never taken time or put effort in creating a single "STANDARD REPAIR PROCEDURE" Designed for beginners, newbies....non technical people. A robust "expert system" that could help saving these machines from the destruction due to poor execution in the "fixing". AA Posts are all over the place, thousands of them...similar, conflicting information, etc. Every black screen post is a "groundhog day". I would think this machine is simple enough development of a simple Diagnostic tool-document - process is feasible. A learning system with videos, documents, diagrams, step by step....etc.

I realize that you're venting, and it seems that you've been unusually unlucky with your issues. IMHO, all of this is far from typical. I don't think that Atari ever earned a bad reputation for quality control issues with the build/assembly on their shipped computers. Your issues are both unusual and bad. At least worth a reference is Atari's official Field Service Manual, but because your problems are so severe, the fact that you don't have the SuperSALT Cartridge or Test Assembly is something that won't make a difference.

 

Also worth trying (as an experiment to gather more info) is temporarily reconnecting the keyboard and seeing if holding OPTION or if holding START while powering on has any impact on behavior. Any sounds, by chance? What does the RESET button do for you? And, as someone else mentioned, if you have any cartridge, try it. I'm sure you've already unplugged any existing cartridge, joystick, SIO device, or any other accessories plugged into the motherboard. I'd be pretty sure that if a chip is in a socket that you've already resocketed it at least once, right?

 

I'm assuming that you're not using anything crazy/unusual connected to the video output of the Atari that could somehow backfeed a problem into the motherboard that way. But verify/reinforce grounding (between your video device and the Atari computer) if possible or switch to a more basic form of video output (RF, channel 3). Your problems goes beyond what most people face.

 

EDIT: Removed section where I confused the CPU's high NMI line with the HALT line.

 

Just some thoughts and best wishes,

the jmccorm

Edited by jmccorm
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