Atari 800XL Memory Problem

[Ramses]

I've just acquired an Atari 800XL for super cheap as the seller didn't have a power supply and couldn't confirm that it worked. I bought it anyway since it was in mint condition. It's like no one ever touched the thing - no wear or dust AT ALL. I picked up a power supply and video cable and tested it and I'm getting the memory screen with several red blocks and one missing block.

 

Now I've done a little research, but I've still got some questions. First of all, it looks like I'm going to have to get some replacement RAM. Will any 4164 chips work? Looking at the screen I attached, how many do you think I'll need? Considering the condition of the computer, I'm curious if RAM can go bad without being used. It makes me wonder if this might have been a lemon and could have other issues.

 

What do you think? Anything else I should check before I try to get more RAM?

Edited September 26, 2016 by Ramses

[Roydea6]

I've just acquired an Atari 800XL for super cheap as the seller didn't have a power supply and couldn't confirm that it worked. I bought it anyway since it was in mint condition. It's like no one ever touched the thing - no wear or dust AT ALL. I picked up a power supply and video cable and tested it and I'm getting the memory screen with several red blocks and one missing block.

 

What do you think? Anything else I should check before I try to get more RAM?

I would turn it on so Basic READY screen is available and the type in a small program. a FOR - NEXT : GOTO 10 and let the program run for several hours +6 and then stop programs and type BYE to get to selftest and let the Memory test run again.

[Ramses]

You'll have to bear with me a little bit as I don't have much experience in these old computers. I don't think I can reach Basic. It boots directly to Memory Test. All I can do is Reset.

 

One thing that seems off is that the Option, Select, Start, and Help buttons have very little resistance and the Reset button does. Is it supposed to be that way or could there be missing parts?

[thorfdbg]

You'll have to bear with me a little bit as I don't have much experience in these old computers. I don't think I can reach Basic. It boots directly to Memory Test. All I can do is Reset.

 

One thing that seems off is that the Option, Select, Start, and Help buttons have very little resistance and the Reset button does. Is it supposed to be that way or could there be missing parts?

The resistance of the keys is normal this way. Reset should be harder to push than the other keys.

 

However, the memory problem could be anything from a damaged MMU, a dead delay-line to incorrect refresh due to a damaged ANTIC. If you have a second system, try to swap parts back and forth to find the defect.

[Ramses]

However, the memory problem could be anything from a damaged MMU, a dead delay-line to incorrect refresh due to a damaged ANTIC. If you have a second system, try to swap parts back and forth to find the defect.

 

Yeah, that's what I was worried about. Unfortunately, this is my only 8-bit computer so it looks like I'm going to have to buy another one or buy and replace all the RAM and hope for the best. I'm guessing I'd have a hard time finding a replacement MMU or ANTIC separately.

Edited September 27, 2016 by Ramses

[Rybags]

I'd lift and reseat the memory chips before buying new ones. Also do the minor 7400 series ICs, some are involved in memory selection.

 

The requirement for any Ram on Atari is 250 nS or better access time. For the 4164 type chips that should be the case anyway. The last 2 numbers of the long-form part # usually indicate speed, e.g. -12 would mean 120 nS.

[shoestring]

Those DRAMs are sensitive to over voltage. A power supply failure or surge was most likely the cause.

 

If you have no way of testing ram chips just replace the entire 8.

[1050]

The pattern of green/red squares can't be read as to this ram chip or that one. This test just

makes it look like one can. Every ram chip is holding one bit of all 64K locations so by rights

when one ram chip goes south the screen should show solid red squares. It won't because it needs

working ram to create the display in the first place. From there it gets complicated.

 

It is showing something is not right, we can't know until you fix it. Without knowing what it is.

Nice test eh? That's what it's worth. Changing out ram like it's a pair of socks is likely to

not work the best, but you certainly can try it especially if the motherboard is socketed.

Reseating chips advice already given #1 thing to do. Getting a working spare #2. Sys-Check is

still for sale and might be the fastest way to finding out what's really going on.

 

Ram doesn't go bad from non-use, it doesn't go bad from use either - it's probably not bad in the

first place. Chip legs do grow crud and often respond to a proper re-seating thus the advice

taking #1 spot. Swapping good parts for bad ones is a pretty fast way to find a bad part unless

you've got Sys-Check telling you which is your bad part with nothing else done.

 

Most parts are still easy to find, MMU can be made from a GAL for example. 40 pin chips used to

be available as a complete set for $20 or so and not really a problem to get. Lemon speak is

not logical as Spock might say.

[Rybags]

A pattern can indicate an address bus or row/column problem.

 

The 5th/6th dots in the second row should be ignored, they correspond to addresses the Self-Test Rom overlays and don't get scanned.

Also, the first dot gets a pass, I think that the first 1K is also ignored.

 

As for identifying a single bad chip, the touch test is probably worthwhile there. Of course these things are easier to diagnose when you have a working machine to be able to swap components around with.

[Ramses]

Thanks for the info everyone. I did do a "touch test" and all of the RAM chips are cool. The ANTIC chip is pretty hot along with the 6502 to the right of it. The OS ROM and pokey are warm and the rest of the chips are cool.

Edited September 29, 2016 by Ramses

[1050]

This could be a dead ram case where the chips are dead in the water.

 

Ram never run cool unless they are dead. But being dead means you can find them by pinching

down the legs of other ram and placing them over the top of these and by such means it

will now pass the test. If the board is socketed, then no problems just replacing them.

So the piggyback technique really comes into it's own on the dead ram 130XE mainly

because those boards where mostly without sockets where the early 800XL were mostly all

socketed.

 

You did pry up and then push down again all chips in all sockets? They don't have to

be removed entirely just moved up and down preferably three times each end.

 

Starting to sell new for around $2 a pop these days, the days of cheap ram buys

are perhaps behind us?

http://www.ebay.com/itm/252535364576

[Ramses]

Well I received 10 ram chips, tried piggybacking them and got some strange results. When I tried each chip, one at a time, I got the same memory test results for all eight. Then I tried piggybacking all of them at once. I could only get up to 6 at once, any more than that, and I get a black screen. I checked them real closely and it appeared all the pins were touching. I'm not sure if some chips I ordered are bad or not. Some of them result in a black screen if only one is piggybacking.

 

Anyway, after messing around with them for a while, it booted to the Basic screen. I took one off at a time and was able to remove all of them while still getting to the Basic screen. Then I turned it off, plugged in the keyboard, and I was back to the memory test screen. After more fiddling piggybacking the ram chips, I was able to get back to the Basic screen again, this time with the keyboard plugged in. I could type in about 2 lines of code, and then it freezes up. I booted again a few times and tried to get to the self test screen by holding option and I couldn't get to it. It would only boot to Basic.

 

After a while it when back to only booting to the memory test screen with the exact same results as before. So is it looking like the memory just needs to be reseated after all? The soldering looks perfect - no cracks or imperfections. I'm a little worried I'm going to burn the board when I try to work on them as I'm not the greatest solderer and I've never soldered on a PCB before. That said I realize soldering would be involved no matter what the fix turned out to be.

Edited October 12, 2016 by Ramses

[Kyle22]

It's always best to replace them all. Please install sockets instead of soldering the RAMs directly to the board.

[shoestring]

It would work in an open case but I don't know if that would work in all cases. RAM fails in many different ways.

 

Say for example say you have a stuck low bit on the output of the bad chip, piggybacking a good chip would still drive the output low? Or you would have the stuck low bit superimposed over the good output?

 

Best to remove all those DRAMs, install sockets and test them individually.

[1050]

There would be a mix of outputs if the original ram were not dead ram. But note that I

start by saying piggybacking will allow you to know which ram is dead. One bit good

is not dead ram. Although it can happen, dropped bit errors are rare as hens' teeth,

not very helpful typing a treatise on it when odds are this ain't that. It's a

definite possible with sockets and total replacement the same fix in any case.

 

It does sound like some of the replacement rams might be wonky. The ones that get a

black screen all by themselves should be segregated and shunned. Also sounds like a

recent 800XL with few sockets. Good thing is, if you came here to learn how to solder,

you picked the very best motherboard to learn on as they are almost indestructible in

that they can tolerate a lot and be repaired to a very high degree. I would only use

machined sockets to go back with. They do cost more, they are more hassle to find

too. But they do not have the problems of bad connections over time that plague the

cheaper wipe type sockets even when they are double wipe, these will still grow crud

and develop the need to re-seat them. I am at that point in life where I regret

every wipe type socket I ever soldered in.

 

Get and use solder flux, no one worth his salt at soldering even tries it

without their favorite flux on hand.

 

The fact that you are having so wildly variable results sometimes with no ram

piggybacked at all smells like a bad CPU to me. I had one and it showed every

side of crazy stuff possible. But especially lock ups on a random schedule.

Changed it on pure advice and the crazy just went away. Here is where that

spare Atari comes in as so handy to have around.

[Ramses]

Well after a few weekends of desoldering attempts, I think I'm about ready to throw this thing back up on ebay. I removed solder off all the pins for all 8 chips, but I still can't remove a single one. There still seems to be some solder on them, but I'm having a hard time seeing it. It must be on the top side, however the plunger is too big to get in between the chips and the wick doesn't seem to be sucking anything up.

 

I don't see how people do this stuff. Youtube videos make it look easy!

[tjlazer]

Cut all the legs and unsolder each one at a time and use needle nose pliers to remove the pin.

 

 

Sent from my iPad using Tapatalk

[Rybags]

By far the easiest way to desolder DIPs with the added bonus that it's usually non-destructive is to hold a fine tipped iron running down the pin from the component side. Touch the pin only, make sure the board isn't being contacted.

 

About 10-15 seconds @ 230-250 degrees C should be enough, then just suck the solder with a pen type desoldering tool.

All this business of snipping off pins and pissing about with heat, suck, braid/wick is a waste of time. Do it using the proper method then inspect and use the braid where needed, which in case of having done it properly might amount to 2 or 3 pins per chip.

[+mytek]

Also very important: Liquid flux is your friend when desoldering chips. Basically the first thing I do is take a brush and apply a thin layer of flux across all the pins on the chip I wish to extract. Even that rosin flux from Radio Shack will work, although it's very sticky.

 

- Michael

[Kyle22]

Please do NOT use flux from a hardware or plumbing shop! PC Board safe flux only.

 

Something like this: https://www.circuitspecialists.com/835-100ml.html?otaid=gpl&gclid=CNeL9qXiqdACFU5LDQodvVoDFQ

[shoestring]

Well after a few weekends of desoldering attempts, I think I'm about ready to throw this thing back up on ebay. I removed solder off all the pins for all 8 chips, but I still can't remove a single one. There still seems to be some solder on them, but I'm having a hard time seeing it. It must be on the top side, however the plunger is too big to get in between the chips and the wick doesn't seem to be sucking anything up.

 

I don't see how people do this stuff. Youtube videos make it look easy!

 

You need a good,clean tip and a temperature controlled soldering iron is ideal for this stuff. Years of soldering taught me not to use bad quality equipment because then I risk doing damage. Also make sure your tip is tinned with solder before you apply it to anything.

 

Wick works well but its a slow process, I used a Goot desoldering pump for removing chips until I got a proper de-soldering gun, it's fast and easy. Also important to make sure the pin isn't connected with a tiny bit of solder when you attempt to pull the chips out or you risk ripping up traces and the plate through-holes with it.

Edited November 15, 2016 by shoestring

[Ramses]

Alright, you guys have convinced me to give it a few more attempts!

 

Unfortunately, I'm working with cheap tools and I'm not sure how much more I want to spend on this. I'll get some of that PC board safe flux, though I'll need to weigh the better soldering iron and pump against just buying another 800XL. The latter is starting to look pretty tempting, even if it costs more as I got this thing for the games, and not so much for a tinkering project. I just want to play Montezuma's Revenge already!

 

If I do get another machine, I'd have to at least get one that seller claims to have tested. Unfortunately, it seems like most sellers don't test the machine and sell it as is. $200+ seems to be the current going rate for a machine that was tested beyond just making sure it powers on. How much would I have to spend on a soldering iron that would do this job well? Anyone have any specific recommendations? Shoestring, what desoldering gun do you have?

Edited November 17, 2016 by Ramses

[shoestring]

I have a Digitech desoldering station, it's one of the cheaper brands but I haven't had issues with it so far. There are a lot of options in the US but if I had the money to throw away then I'd probably go for a Hakko FR-300, very expensive. There are more affordable options in the $60-$150 USD range.

 

To be honest if you're going to be doing a lot of soldering you'll need one. But if you're only doing this to fix an 800xl and desolder 8 chips then I can't justify dropping that much cash for a small job like that.

 

Get yourself a Goot desoldering pump, they're around $14 USD,practise on a junk PCB board. You might have a tough time removing the remaining solder on some chips. Remember that some pins will have excess solder on the parts side, solder often pools up through the plate through hole in manufacturing during the soldering process.

 

Also a good habit to get into. Add solder to pins before trying to desolder. I find that it's easier to reflow / add some solder to stubborn pins before attempting to remove it with a pump otherwise there's a chance of only removing some of the solder. I kinda do the same thing now with my desoldering gun by tinning the tip with solder. The idea behind this is to minimise exposing the pads to excess heat which can screw a good board. Atari PCBs are good quality and can take some of that abuse but an arcade board won't stand up to the same abuse.

[re-atari]

Alright, you guys have convinced me to give it a few more attempts!

 

Unfortunately, I'm working with cheap tools and I'm not sure how much more I want to spend on this. I'll get some of that PC board safe flux, though I'll need to weigh the better soldering iron and pump against just buying another 800XL.

 

How much would I have to spend on a soldering iron that would do this job well? Anyone have any specific recommendations?

How about these:

 

http://www.banggood.com/Mustool-MT223-60W-Adjustable-Temperature-Electric-Soldering-Iron-with-5pcs-Solder-Tips-p-1077119.html

 

or, if you want a bit more luxury:

 

http://www.banggood.com/BAKON-950D-75W-Mini-Portable-Digital-Soldering-Station-with-T12-Tip-p-982824.html

 

Add to that desoldering wick or a pump and liquid flux, and you should be set for occasional soldering jobs during the coming years.

 

I don't own either of these soldering irons, but have heard positive things about them. I myself have been using a 35W non temp. controlled soldering iron for 20 years now, and do anything up to small SMD parts with it. It cost me about $20 back then, and the thing just won't break down. If it ever does I think I'll switch to the Bakon iron.

 

The satisfaction of fixing stuff is immense. Seeing something you've worked on come back to life is priceless. And you'll have gained valuable experience along the way.

 

re-atari

Edited November 17, 2016 by re-atari

[hueyjones70]

I am working on a 800XL that doesn't go to self test when I boot while pressing OPTION. Any ideas of the possible cause.