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JeffJewell

Atari 800XL Spelunking

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I still have my Sunnyvale Heavy Sixer, my constant companion since Christmas morning, 1977.

 

My original 1979 Atari 800 still runs... as does my original 1050 drive (because I couldn't scrape up the $ for an 810, while it existed as a commercial product).

 

I am now spelunking through a collection partly of my own making at the time, and partly of my rebuilding on the second hand market after the time. I am currently spending some time with an Atari 800XL, and I hope that folks can point me in a couple directions.

 

First up, the 800 XL I'm working with isn't working correctly. It runs from some cartridges, but not all of them (AtariWriter has allowed me to check the keyboard, which seems to be completely working. Two different Pac-Man carts failed, Miner 2049er worked). It does not seem to check the SIO chain at all (known good drive on known good cable with known good floppy doesn't even result in a hey-look-I'm-here drive light flash at boot up). Machine goes straight to memory test unless one of the successfully booting cartridges is in place.

 

The memory test gives green for both ROMs, then green for 32 RAMs then red for 8 RAMs.

 

Wanted to see if anyone had any red flags go up at that set of symptoms. First Googlings suggest I might need to replace the BASIC ROM or the Atari OS ROM, based on the SIO funkiness.

 

I have found it to be a Chelco Rev A2 motherboard with the Alps keyboard.

 

I've also wanted to necro-post on a couple of things along the way... as I am digging through my Atari history and comparing it with the internet's version of things, I'm finding a lot of desirable information taunting me from behind dead links. What resources do y'all still find active and relevant with regard to Atari hardware versions and revisions?

 

I'm back, Atari-verse.

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no, sounds like you have bad ram just as the self test suggests....

check ram, MMU, and support chip. off chance basic being bad.

based on what you've mentioned.

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Cool... so what does the 32 good, 8 bad actually tell me... the RAM is those eight chips on the right side of the mb, right? Haven't found a table to equate the apparently 40 memory check blocks to the allegedly 64K memory of the 800XL. Should I look at replacing all of them? They are all socketed on this mobo. I've got a Harbor Freight multimeter, is there a way I can check the bad boys individually?

 

Thanks so much for the reply, by the way. I've got that newby-getting-back-into-it energy, and any new rabbit hole is a good one for me. Like I mentioned, dead links seem to be my nemesis right now, if there's some place I should be looking before I post here, please direct me there.

 

A sincere thank you to anyone who is still checking these boards with the hope of annotating and spreading the Atari platform.

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Sounds almost like the system thinks a cart is present when it's not, cartridges have a flag which determines if a disk boot is allowed, plus the system intermittently thinking a cart is present could cause spurious problems when accessing the 32-47K address region.

 

That could come down to Ram being probably OK but something in memory select such as MMU, PIA or even the cartridge port itself (you could pull the plastic interlock device off to inspect it closer).

 

If you have a known good machine as well of course it makes diagnosis a bunch easier.

 

Though you say you've got an original 800 - so maybe try the Basic cartridge from that.

Then try stuff like

? FRE(0)

should return about 37K if no Dos present.

GR. 8

should give a clear screen, if glitching occurs then it's a Ram or memory select problem.

Edited by Rybags
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I have several other machines to test against. There's a 320XE with an XF551, XF351, and an MIO in the bedroom.

 

Okay, so now I'm wondering abut the cartridge port.

 

Using an old BASIC cartridge, I've gotten the thing to boot to Basic once or twice. It is mostly going back to the Memory Test screen.  I just got 4895 as a response to the ? FRE(0) command.

 

GR. 8 gives me:

ERROR-     9 AT LINE 29441

 

Again, that is with the BASIC cartridge inserted in the 800 XL.

 

And after doing that, the ? FRE(0) gives me 63311. Repeatedly.

 

The stability of the machine trying to read this cartridge is suspect. It just flaked back out to the memory test screen from Basic. There is a BASIC cart in this XL at the moment.

 

So... cartridge port, I'm looking at you?

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The machine still seems to run fine with an AtariWriter cartridge... two different AtariWriter cartridges, now that I'm focussed on it.

 

Atari Logo cartridge boots to (c) 1983 LCSI ALL RIGHTS RESERVED WELCOME TO ATARI LOGO.

 

BASIC cartridges are now powering up to blank screens.

 

And now it took me a minute to get the AtariWriter cart booting again.

 

So, something with the cartridge port not being consistent?

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Fix the ram first.  Then troubleshoot more.  Replace all 8 then you can narrow down each chip to find faulty ones.  

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AtariWriter is a 16K cart, Basic is 8K.

 

Without trying to turn this into some cheap betting fest, I'd put odds on that the Ram itself is OK.

 

I guess your 320XE probably has the Ram soldered in or is a 2 or 4 Ram chip machine from the factory - in which case swapping it over isn't so easy.

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4 minutes ago, Rybags said:

AtariWriter is a 16K cart, Basic is 8K.

 

Without trying to turn this into some cheap betting fest, I'd put odds on that the Ram itself is OK.

 

I guess your 320XE probably has the Ram soldered in or is a 2 or 4 Ram chip machine from the factory - in which case swapping it over isn't so easy.

MMU or decoding logic issue then?  Dead basic chip?

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Maybe pull the Basic chip out to see if behaviour changes.

Though any cart present should override Basic anyway.

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The PIA chip is involved in memory access, as are most of the discrete logic chips on the board. The weird SIO behavior could be a lot of things. When I encountered a similar problem with a 1200XL, it was a POKEY problem, even though sounds and keyboard both worked fine (POKEY handles all three). 

 

Another possible test, if your console keys are working, is power on with START held down - you should hear the cassette loading sound, prompting you to press PLAY on your cassette and then RETURN on the keyboard to start loading. You don’t actually need a cassette program recorder though to see if the machine will at least make the loading tone. If it doesn’t, I’d suggest a POKEY problem.

 

Query: how many chips are soldered on the main board? I have a similar Chelco 800XL and every single chip is socketed, even the 74-series logic. If you have a similarly socketed board, it can often be worthwhile to very carefully remove all the chips, spray contact cleaner into the socket wipes and reinsert the chip. That helps remove any old surface corrosion on the chip legs and sockets. Allow the cleaner to evaporate for a few minutes before another power test. 

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Yes as Dr. Venkman says it might just be old surface corrosion on the chip legs. If you don't have contact cleaner on hand, carefully re-seat each chip ten or so times to wear off the corrosion. That might fix the machine. Use a chip puller, not a screw driver please. lol they cost $3.

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cleaning works magic, and yes the PIA could be an issue,

I always push the chips slightly in before I pull them, it can prevent swipe damage...

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Thanks to everyone who responded! Great to get quick feedback on retro hardware projects like this.

 

I understand the question about my having other machines, now, and yes, I have a working and very similar internally 800XL for comparison. I have attached a file of my workbench... the flaky 800XL is toward the back, and the working one I'm currently dismantling is up front. Next step is to remove the shielding on the good mobo.

 

Having two dismantled 8-bits at once is more than I was planning for on my current workspace, and I'm a little wary of yanking stuff out of my working machine to try and Frankenstein the other one, so I'm going slow on that part.

 

Dr Venkman, yes, it appears that everything on the "bad" mobo is socketed... I'll be getting into the working one's shielding soon.

 

For what it's worth, trying to start the offending machine while holding down the Start key usually goes straight to the self test. Once or twice it went to a BASIC READY prompt with two parentheses at odd places on the screen. But almost always the self test, never a cassette sound.

 

I've been trying to document what I'm finding out about taking these things apart and the differences in what you might find there, this particular machine is documented in this post. In the post, the SIO handicapped machine is 800XL-b, and the good machine is the reference 800XL. I've been following all kind of rabbit holes concerning keyboards, motherboards, serial numbers.... I think my next spelunk will involve Atari's IC iterations.

 

I guess my next step on this particular 800XL is... well, I wanted to say Radio Shack, but I think I'm a couple decades too late on that. Can y'all suggest the best products for my cleaning up stage? Not thinking about RetroBright or case aesthetics, just wondering about cleaning rust and whatever else off of old circuit boards. Initial Googling suggests that I can clean the rust off this weathered shielding, but I will then need to seal it somehow to keep it from rusting again.

 

I'm also going to look around for another source of test 800XL chips aside from my "reference copy" machine.

 

Thanks again for the tips and the encouragement!

7D8DB78A-A054-4D54-BBCF-DD171428F6E8.jpeg

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Anti-static brush kit and IPO 99.9 pure anhydrous to clean the boards. You might consider ELECTROLUBE SAFEWASH 2000 (No it's not 19 years old) for cleaning. Wouldn't get it on my hands. Also some solder mask in a tube is good to have on hand if you need to scrape any off (you probably won't though unless there is rust or corrosion). Should be reapplied to protect the traces, etc. 

 

White vinegar is often suggested for corrosion/rust but apparently its hard on the copper traces. You might use it on your rusty RF shield, separately. Then some rust protection afterwards.

Edited by Sugarland
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I clean with 90%+ isopropyl alcohol and a nylon toothbrush, both available at any convenience store. I don’t both with solder mask stuff - I’ve never needed it and I can’t imagine a repair where I’m likely to. For electrical contact cleaning per se, I use Deoxit purchased from Amazon. Best stuff around. Second choice would be something like CRC branded stuff from an auto parts store but be sure to use one safe for use on plastic. 

I do heartily recommend you dig into SAMS or a similar reference and methodically trace connections between components and measure voltages or pin activity with at least a logic probe - expected IC activity charts per pin are listed in SAMS. 

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Deoxit can also be found at music stores, e.g. Guitar Center or Sam Ash,
if you don't want to wait for it to ship. Price might be a little higher,
but you don't pay shipping.

The CRC stuff is available 24/7 if you have a Wal-Mart within driving
distance. Look in the automotive department. I've gotten good results
with it on Atari stuff (e.g. filthy cartridge ports).

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I appreciate all the help. I've got my shopping list mostly ready.

 

DrVenkman, is a specialized logic probe a separate purchase, or can I do those tests with a regular multi-meter? If I'm reading at those charts correctly (great tip on the SAMS, by the way, I hadn't run across them yet) it looks like I'm just checking for low/high on certain pins when the machine has power. The specialized logic probes I was finding on initial search seemed to be automotive oriented.

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2 hours ago, JeffJewell said:

I appreciate all the help. I've got my shopping list mostly ready.

 

DrVenkman, is a specialized logic probe a separate purchase, or can I do those tests with a regular multi-meter? If I'm reading at those charts correctly (great tip on the SAMS, by the way, I hadn't run across them yet) it looks like I'm just checking for low/high on certain pins when the machine has power. The specialized logic probes I was finding on initial search seemed to be automotive oriented.

I use a <$20 Elenco logic probe from Amazon for basic diagnosis. A typical multimeter will not be able to do more than confirm Vcc and Vss for the chips. The logic problem will give you little LED indications of high (+5V) and low (0V) and will click fast or slow to indicate high or low frequency pulsing activity for address, data and clock lines. I used mine to diagnose and restore what I call my “Ugly Duckling” 1200XL a couple summers ago. I determined the machine had 3 bad sockets that all needed to be replaced. 
 

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