Now I've done it.

[russg]

I have a 800XL, fully socketed, motherboard that I've tried to resuscitate for years.

I unwisely removed the keyboard jack, trying to use the computer for parts.

I went on the attack with Sam's Photofact and official Atari 800XL Field Service manual,

oscilloscope, logic probe, multimeter and a fully functional other mb for chip swapping.

I located a constant high voltage A7 address line at pin 16 of CPU and other places

that do A7. It gets good pulses on A7 at pin nine of the drams and pin 9 of U27. At

other A7 points, it goes constant high.

I'm trying to learn how the A8 works.

Bottom line. I've now got three mb that don't work. I seem to destroy

something by trying to test 64x1 drams. I had a 256k Newell. It

now gives the grey screen.

I get a clock waveform on pin 11 of U18.

I've just about swapped every chip.

I'm now down to transistors, capacitors, resistors, etc.

Any advice on how to proceed would be appreciated.

Is there something that I break by trying a 64kx1 dram

on a 256kx1 Newell?

The symptom I get is a solid grey screen, and sometimes a

garbage display with dancing random characters. It seems

as if the display list is corrupted.

I'm pretty sure I've shorted across adjacent pins with the logic

probe sometimes.

Edited September 29, 2014 by russg

[Roydea6]

ROFLMAO

 

 

 

 

Edited September 29, 2014 by rdea6

[+bob1200xl]

The A7 pins on the DRAMs are not the same signal as the A7 on the CPU.

 

You can get a pretty good idea of what is happening by paying attention to the video when you power on. Video comes up randomly when you power on. May be green or red, no video to speak of, just a blank screen. Early in the code the video gets reset to a blank, grey screen and you hear a little 'pop' on audio. If you get that far, the CPU and part of the ROM works, sort of. If you don't get that far, the CPU and ROM aren't running. At this point it does not matter if DRAM works or not.

 

Bob

[+bob1200xl]

I think you can plug 256K DRAMs into a stock 800XL, but you may have a problem with pin 1 REFRESH if you use 64K DRAMs in a 256K machine.

 

Bob

[Paul Westphal]

I had a 600xl that I replaced every chip twice on, and finally gave up. Got a new one from best electronics cheap. You may or may not get a socketed one. A+ for trying though....

[russg]

The A7 pins on the DRAMs are not the same signal as the A7 on the CPU.

 

You can get a pretty good idea of what is happening by paying attention to the video when you power on. Video comes up randomly when you power on. May be green or red, no video to speak of, just a blank screen. Early in the code the video gets reset to a blank, grey screen and you hear a little 'pop' on audio. If you get that far, the CPU and part of the ROM works, sort of. If you don't get that far, the CPU and ROM aren't running. At this point it does not matter if DRAM works or not.

 

Bob

I get a color flash on the 256K before the blank grey screen. All three XL go to a blank grey screen in just a moment.

A7 is pins 9 of the drams, pin 9 of the U27 also. A7 goes out pin 11 of U27 to pin 16 on the CPU. I get a constant

high on A7 at U27 pin 11, should be a pulse. A7 goes to pin 1 of BASIC ROM and pin 3 of OS ROM. Ahh well.

The pulse gets lost on A7 at pin 11 of U27,also goes constant highs at pin 16 CPU, 1 BASIC and 3 ROM. It should,

they are all on the same line.

Edit: That's just on one XL. The 256K Newell has pulses on A7 at pin 16 CPU, 1 BAS & 3 OS.

The original problem XL mb doesn't get pulses on A7 at the pin 9 of the drams or anywhere else.

All three are different.

Edited September 29, 2014 by russg

[russg]

ROFLMAO

 

 

th.jpg

 

 

Yeah, it is funny. But I want to cry.

[+bob1200xl]

If you reset the screen to grey then A7 must work. Look somewhere else.

 

Are you running a stock 800XL or one with a 256K upgrade? On all three you get a grey screen?

 

Bob

[pixelmischief]

"You are likely to be eaten by a grue."

[russg]

If you reset the screen to grey then A7 must work. Look somewhere else.

 

Are you running a stock 800XL or one with a 256K upgrade? On all three you get a grey screen?

 

Bob

I have three 800XL that I'm working with. One is an oldest that I messed up years ago and I've been trying to resuscitate.

My main method is to swap chips. The one I'm most concerned about now is my 'test' mb. It was fine until I did something that made

it go to a solid blue screen at power up. I also messed up a 256k Newell, trying to test a 16k dram in the bottom dram socket.

The 'old' one and the 256k are secondary right now, until I can get my 'test' mb working again.

The test mb has the pulse signal at pin nine of drams and pin 9 of U27, but solid high at pin 11 U27 and pin 1 of BASIC and 3 of OS.

I get good pulse on CPU pins 9 to 15 and 17 to 20, and pins 22 -25. Pin 16 of CPU is A7 and constant high.

[Marius]

You should work the other way around in this state.

 

Get yourself (if you still have one) a socketed Atari 800XL and exchange 1-by-1 IC's and after every swap try the working 800XL. As long as it keeps running without issue you are pretty safe (not completely strange enough, but in this state it is important to check whether the IC's are working or not).

 

And perhaps a dumb comment, but make sure you do not make 'stupid' mistakes due to fatigue. (I mean putting in IC's backwards or bending a pin while inserting it in the socket so that pin doesn't make contact, but from the outside you can't see the pin is bend!) or leaving a pin out of the socket. etc. You'll be surprised!

[russg]

You should work the other way around in this state.

 

Get yourself (if you still have one) a socketed Atari 800XL and exchange 1-by-1 IC's and after every swap try the working 800XL. As long as it keeps running without issue you are pretty safe (not completely strange enough, but in this state it is important to check whether the IC's are working or not).

 

And perhaps a dumb comment, but make sure you do not make 'stupid' mistakes due to fatigue. (I mean putting in IC's backwards or bending a pin while inserting it in the socket so that pin doesn't make contact, but from the outside you can't see the pin is bend!) or leaving a pin out of the socket. etc. You'll be surprised!

I do have one more 800XL, that works. It is an Omnimon unit and I don't want to go swapping chips with it, that's how I got in this mess to start with.

I'm hoping to learn about how the A8 works while I'm at this. I have to figure out the problem with my 'test' mb without swapping chips. Also, I think

I looked in my Omnimon 800XL, and it doesn't have socketed drams and other chips aren't socketed.

Edited September 30, 2014 by russg

[Tickled_Pink]

Well, one thing you've probably learned from it is ... if it 'aint broke leave well alone. If it is broke, don't make it any worse.

 

One thing I have learned from tinkering with ageing electronics is that they're probably far more temperamental than when they left the factory. The 800XL seems to be amongst the most temperamental of the bunch. I have a couple of them in a non-working condition in the garage. I've also had a 65XE and 130XE fail on me after a bit of minor tinkering. One of the 800XLs I have is heavily modded. The mods have been done in a professional manner but it is very flaky. It's why I have a couple I keep in an untinkered-with state.

 

If you have just one that's untinkered with, DO NOT tinker with it. Leave it alone.

[Marius]

Well that's another reason for me to stick with original unmodified atari's. My experience is that as soon as you go mod your atari, you are going to rely on these upgrades, and as soon as your atari stops working, you can not simply move to another, since it lacks all the bells and whistles.

 

Next to that, upgraded atari's seem to go nuts sooner than original atari's (well in my case).

 

Only exception on that rule are stock Atari XE computers with the MT brand DRAMS, which die anyway... whatever you do with these machines.

 

Since I decided to stay away from internal upgrades, I suddenly had a very interesting stock of computers. All powerful, and ready to use. I love that.

[+Larry]

Got to agree with Paul -- for $39.95 + postage, you can have a new, prime Taiwan 800XL mobo. Of course, the postage per unit will be less if you buy two...

 

Don't think of it as losing an 800XL, but rather as gaining a donor board.

 

-Larry

[+bob1200xl]

If you have a blue screen then you never get out of the ROM. Bad OS ROM, CPU or MMU. You can leave POKEY and PIA out of the computer and you'll still get through the ROM.

 

You need to swap the chips from your failing m/b into a good m/b and test them one at a time. A scope only helps when you have a pretty good idea what is happening. What you need is a logic analyzer that can trace the RESET code. And an OS listing... Not the kinds of things that most people have.

 

Bob

 

 

 

I have three 800XL that I'm working with. One is an oldest that I messed up years ago and I've been trying to resuscitate.

My main method is to swap chips. The one I'm most concerned about now is my 'test' mb. It was fine until I did something that made

it go to a solid blue screen at power up. I also messed up a 256k Newell, trying to test a 16k dram in the bottom dram socket.

The 'old' one and the 256k are secondary right now, until I can get my 'test' mb working again.

The test mb has the pulse signal at pin nine of drams and pin 9 of U27, but solid high at pin 11 U27 and pin 1 of BASIC and 3 of OS.

I get good pulse on CPU pins 9 to 15 and 17 to 20, and pins 22 -25. Pin 16 of CPU is A7 and constant high.

[russg]

If you have a blue screen then you never get out of the ROM. Bad OS ROM, CPU or MMU. You can leave POKEY and PIA out of the computer and you'll still get through the ROM.

 

You need to swap the chips from your failing m/b into a good m/b and test them one at a time. A scope only helps when you have a pretty good idea what is happening. What you need is a logic analyzer that can trace the RESET code. And an OS listing... Not the kinds of things that most people have.

 

Bob

 

 

 

 

If you have a blue screen then you never get out of the ROM. Bad OS ROM, CPU or MMU. You can leave POKEY and PIA out of the computer and you'll still get through the ROM.

 

You need to swap the chips from your failing m/b into a good m/b and test them one at a time. A scope only helps when you have a pretty good idea what is happening. What you need is a logic analyzer that can trace the RESET code. And an OS listing... Not the kinds of things that most people have.

 

Bob

 

 

 

I've put the computers back on the shelf. Swapping chips was/is my idea of going about finding a problem. I had/have the good mb that booted to READY. I tried swapping

all the chips, one at a time. Somehow, I shorted something with my probing with the logic probe. I swapped OS, CPU and MMU, I'm sure. Knowledge of operation is lacking,

like I don't know the sequence of power up. I do have the 150 page 'OPERATING SYSTEM USER'S MANUAL' which is 150 pages of OS B source code. I quickly looked

in it to see if I could find RESET code section. I also have the HARDWARE MANUAL, which if I read might enlighten me. I have my homework set, read some of the

sources I have. It is real easy when probing chip pins to slip off and short two pins. I ordered some mini clip test leads so I can better scope pins on chips. I made

a wire loop to put on a chip pin, which probably shorted. My Sam's gives scope pictures.

I'm disappointed that I messed up two good computers trying to fix the one computer. I will come back to it. And I will try to read and understand the documentation

I have.

[+bob1200xl]

Well... there is a learning curve when you try to fix something. As suggested, you can just buy a new m/b for a reasonable price or you can spend the time, energy and frustration learning how to bring these guys back to life. If you broke one of your systems when you were trying to fix another, you need to know why and how so you won't make that mistake again.

 

Bottom line is that buying a new m/b is more efficient but less educational than fixing one.

 

Generally, shorting any two pins does not do any permanent damage.

 

Bob

[russg]

Well... there is a learning curve when you try to fix something. As suggested, you can just buy a new m/b for a reasonable price or you can spend the time, energy and frustration learning how to bring these guys back to life. If you broke one of your systems when you were trying to fix another, you need to know why and how so you won't make that mistake again.

 

Bottom line is that buying a new m/b is more efficient but less educational than fixing one.

 

Generally, shorting any two pins does not do any permanent damage.

 

Bob

Thanks, Bob.

I ate dinner and thought about 'RESET' code. That would be WARMSV at $E474, 'Initialized to $F11B'. So I do know where to look in the source code.

[Muzz73]

Got to agree with Paul -- for $39.95 + postage, you can have a new, prime Taiwan 800XL mobo. Of course, the postage per unit will be less if you buy two...

 

Don't think of it as losing an 800XL, but rather as gaining a donor board.

 

-Larry

 

Absolutely... I've posted it on other threads, but I'll tack it up here as well... I bought two 800XL boards NIB from Best at $40/ea, just for spares, while the deal lasts. I popped them open and BOTH were shiny and new, complete with RF shielding attached and FULLY socketed when I peeked underneath the RF shield! Get one before they're gone!

[+Stephen]

I'll silently keep hoarding my 3 new 1200XL mobos

[+Larry]

I'll silently keep hoarding my 3 new 1200XL mobos

 

Oops! It's no longer "silent!"

[+DrVenkman]

I'll silently keep hoarding my 3 new 1200XL mobos

 

I've got two, both installed in working machines. One of those machines is almost cosmetically perfect. The other ... eh, she's got some battle scars. But at least she works great!

[_The Doctor__]

You need to use a pin guide/protector on you probes or you can rely on frying many more things!

It's just a plastic piece with a notch in it and a hole for your probe... or buy a probe that has it molded right on it! I cry a little bit inside every time some on destroys an Atari. Especially when there is no reason to do so... Get the proper tips on those probes!

Edited October 16, 2014 by _The Doctor__

[_The Doctor__]

I urge you to let someone sort out the good chips from the bad at this point.... Replace bad caps on motherboard....and while all the socketed chips are out check remaining chips ensuring none are shorted inspect the board with bright light and a strong magnifying glass... make sure no chip or component is discolored/cracked makes sure nothing is bent over and shorting or twisted...

 

the chips that remain soldered to the board can be checked to make sure they are not shorted with a careful use of multimeter first from ground to all other pins (watch polarity of meter!) and from positive to pins..

 

check diodes on board make sure they only read in one direction.

 

this is just a start.. lastly you can always send the boards without the cases(saves on space and shipping) to get repaired... I know Atarimax has had great success fixing Ataris mb's for their customers....

 

NOT ONE MORE ATARI DEATH NOT ONE MORE NOTE ONE MORE IN THE TRASH!