Atari 800XL repair: Black screen at power up

[@drgusman]

That antic chip is visibly busted, there is a bulge in the middle of the package, I have seen that same effect in other burnt IC's. Those old plastic packages tend to bulge and break when they're overheated.

[@SidneyCritic]

4:00 I thought I spotted 2 bulges on it - lol -.

[@SockyNoob]

Kinda silly that Atari never thought to put a heatsink on it. Not like the idea was unheard of back then. They probably did math and figured the chip would last long enough to justify cutting costs and not putting one on it. Definitely a warning to other Atari 800 owners to put a heatsink on their Antic chip before it melts itself.

[@SockyNoob]

​@@SidneyCritic appears to be between the 9 and - at the bottom.

[@beatadalhagen]

I noticed the pips right away, but it turned out to be a decent troubleshooting session.

[@Agent24Electronics]

That chip looked suspicious from the start. Definitely looks like a burn-hole in the middle. Also some other blemishes around the edges but that could just be molding marks.

[@markwrightrf]

I can remember, as a kid, when my beloved 800XL developed a fault in the power supply connector that caused intermittent crashing and rebooting... my school friend offered to swap his working ZX Spectrum for my superior but dying machine along with all peripherals and software. I agreed. I watched him take less than a minute to re-flow a solder joint and the machine was good as new. I took a walk of shame, ZX Spectrum in my school bag, wondering what I'd done. We don't talk anymore.

[@fastbeta]

I made my own ZX Spectrum 128K with Betadisk Interface and VGA output on RP2040 PI Pico. Firmware is available for everyone.

[@CalculatorObsessed]

That’s just mean. A real friend would have fixed it for you, although I could understand if he borrowed it for a while as a reward.

[@JamsterJules]

Legend has it, it still works...

[@TheGreatAtario]

If he'd been smart, he'd have made the repair when you were gone and then later told you all about what a nightmare it was to fix and how you're lucky you didn't have to deal with that hell

[@robwebnoid5763]

@@CalculatorObsessed ... Definitely a bad friend. It was a hidden agenda to swap computers & perhaps have the better one.

[@tschak909]

Hi Adrian! Thom here. Yup, the ANTIC is quite literally the bus master of the system. The SALLY 6502 slaves to it, so that ANTIC can steal cycles dynamically depending on the active display list, and thus ANTIC provides all the primary clock phases needed by the CPU and other things. Also, yes, C56 was Atari's attempt at "DRAM refresh jail bar" removal ugh. :) It's the business end of a low pass filter.

[@Martin.Krischik]

Was just about to say the same. No ANTIC no clock for the CPU.

[@KennethSorling]

"I know nothing about Ataris!" . Adrian, you're one of a kind!

[@ezContents]

Great video! It's nice to see that the Atari 800XL schematics I created are proving to be useful. 🙂

[@nickolasgaspar9660]

indeed they are!

[@emmettturner9452]

My first Atari 800XL repair was my first Atari 800XL. It literally broke while I was borrowing it to test, forcing me to buy it and repair it. It worked once, then I switched cartridge and one of the cartridge pins bent leaving me with a black screen. I couldn’t even boot without a cartridge. I switched from Atari Basic to Pitfall II when it happened but didn’t do anything funny to make this happen. To fix it I desoldered the cartridge slot, ejected the pin, straightened it, and swapped positions with a vestigial pin. I recall the RF shielding was a nightmare on mine since you had metal tabs holding the shields together that wouldn’t simply release when you twist them.

[@Sozzled39]

My favourite little 8-bit computer is the 800XL. Glad you got this one going Adrian!

[@borayurt66]

I clearly saw the pin hole on the Antic chip when you were trying to show us the "OK" writing on the CPU at the beginning of the video. It is where all the magic smoke escaped...

[@nickolasgaspar9660]

indeed! cool remark!

[@andyhu9542]

I'm a long-time viewer and huge Atari fan. I just want to say: finally, an 800XL repair video!

[@gvii]

That clip you're using to probe the chips would be really easy to whip up if you have access to a 3D printer. Pretty simple design, but I can see how it would be incredibly useful. Very cool. Also really cool to see an Atari. When I was a kid, my parents had an Atari 800 and a 2600. When I got a little older, they bought me a 1200XL and a cassette drive. Later on I got a floppy drive. I used the heck out of that thing playing games and punching in Basic programs that came in one of the computer magazines that I can't remember for the life of me. I really miss it. Unfortunately, my Mom tossed it sometime after I moved out along with a C64, 3 Vics, and a boatload of peripherals and carts. Man, I was bummed out when she told me, lol.

[@gmirwin]

That's our generation's version of "Mom threw out my Babe Ruth and Willie Mays baseball cards."

[@richardkelsch3640]

That bodge needs a 100pF cap in series, else you are sending out DC to the chroma output. POKEY has 4 voices when in 8 bit timer mode. These voices can output tones or noise. You can change modes where it combines two channels into a 16 bit precision channel (more accurate notes).

[@adriansdigitalbasement]

Thanks on both parts. It's interesting I looked at another 800XL I had modded in the past, and I did way more mods to the video circuit, and the picture quality is much better than this one. Problem is, I don't recall what I did!! Luckily most (all?) video input circuits tend to have DC blocking caps on them already, so it's at least not inherently dangerous. (But definitely good practice to have it on the output side)

[@fragalot]

Antic chip is responsible for the majority of the graphics, and it generates the TV signal. It's not really known for being hot (or any of the chips) at least not in the 80s. The 800XL barely has any ventilation nor does i have anything connected to it for thermals. The RF shield just hovers over all the chips and dosen't cool anything. The GITA (the one to the left of the Antic) also plays a role in graphics, that entire section is for video, as it leads up towards the RF modulator and monitor port. At the right next to the CPU is the PIA chip which I forget what it does exactly. Above it is the Pokey chip which is responsible for audio, and I/O. Above those at the top right corner is the BASIC ROM, and below that is the OS ROM.

[@HH-Thorsten]

I've already seen at 4:00 that the Antic Chip looks a bit strange on the surface. Like been too hot. I would have exchanged it right away without measuring, but then you would only have had a very short video. Still, a very nice and entertaining video ;)

[@rabidbigdog]

MOAR Atari thanks Adrian. Good for you sir. Best 8-bit machines ever made, designed by legends (Miner etc).

[@RetroJack]

Thank you for showing the URL of the schematic PDF - so many other KZbinrs crop the capture so that only the document or part of it is visible. This, among other things, is one of the reasons I keep coming back to this channel!

[@JosepsGSX]

What a nice lesson. I actually have an 800XL since back in the day, but last time I tested was working fine. I will probably try the mod for the video and maybe add some heatsinks. The way to diagnose procedure is the actual treasure for me. Hopefully I will be able to use this a guide later. Thanks!

[@mnemo70]

I see an 800XL, I click "Like". :-) Like for many others here this also was my first own computer.

[@tigheklory]

Nice job fixing that Atari 800XL! I look forward to your skills on a Coleco Adam!

[@ovalwingnut]

Did I just hear you say that the "potentiometer potentially adjusts the color carrier?".... See, now that's humor! 25 points awarded.

[@Mrshoujo]

Thank you for showing more Atari Love. ❤ Rotten for an ANTIC going bad like that. You got to the root of the problem pretty quickly which is a sign of the nice straightforward design of the 800XL.

[@tim1724]

SALLY is a 6502B with an added HALT pin to allow the CPU's clock to be halted during DMA. Older Atari computers had an external circuit for that; SALLY allowed them to remove four chips from the motherboard. SALLY was originally called 6502C but Atari later changed the name to SALLY because the name 6502C was already in use for standard 6502s that are rated for 4 MHz operation. (6502A is rated at 1MHz, 6502B at 2MHz, 6502C for 4 MHz. SALLY is a modified version of the 6502B, and is thus rated for 2 MHz.)

[@adriansdigitalbasement]

AH! Ok that makes sense. Does asserting half also float the data/address lines? (I assume so as this would be needed for DMA operation unless there are buffers to disconnect the CPU like on the Apple II)

[@tim1724]

@@adriansdigitalbasement Yes, it does float the bus when HALT is asserted.

[@braschlosan]

Would it be possible to revert a Sally system to using the four chips?

[@PlumGurly]

@@braschlosan-- it would be, but you might not have room. You'd probably need the other system board. Of course, one might be able to get a 65C02 to work with less effort. Sure, there would be the instruction set issue, but it should be easier since you have the BE line.

[@robwebnoid5763]

And what does "SALLY" mean? I know Atari used female code names, so is Sally a name based on a real person?

[@griffinretro]

As a tip for KiCad, if you hover a line and press the tilde key, that net will be highlighted making it very easy to see where a signal is used.

[@wizard-pirate]

that was a pdf of a kicad schematic

[@PapiDoesIt]

All of my brothers and I (except the youngest) had Atari computers. I had the 1200XL, and I was mostly interested in just playing games. Between us all, we had the entire spectrum of the Atari computers.

[@ovalteen4404]

The "oscillator circuit" you are talking about is actually a voltage doubler. The output will be around 9V. The Atari's color carrier generation scheme is to run the 3.58MHz clock through a 14-stage delay register. The potentiometer adjusts the speed of the ripple through the delay register by affecting how much voltage is supplied. Color is generated by tapping a particular stage of that register based on color index n, resulting in a phase shift of nπ/7 when the potentiometer is properly adjusted. White and black do not sample the delay register at all, since neither white nor black are on the color wheel and therefore have 0V color carrier.

[@wuuwuuzululu9243]

600xl was my first "real" computer. My brother had the 800xl. Fantastic time. Thanks for your videos, love them!

[@andrewclegg9501]

@@jkeelsnc and take little room on the desk

[@chrisc8156]

Same here - 600XL was my first computer too.

[@DavePoo2]

65XE was my first computer. A close sibling to this computer.

[@andrewclegg9501]

If you put a PAL ANTIC in there, it will get 50Hz output with NTSC colour. Useful for running some PAL demos and games. Not all, but much more than a NTSC machine.

[@adamv242]

Always appreciate Atari content. Thanks, Adrian.

[@m8528]

Hi Adrian, love your channnels here, discovered you 2 years ago, grew up with my first pc in 1987, being 7 years old, my mom had a company who bougt an olivetti 386 sx with 20MB harddrive, 4MB of ram an a ega card, sufficient to play leisure suit larry that same year, guues I was bit to young to play it but loved that machine... hooked ever since amiga commondore and whatever, so big respect for what you do....

[@yarunibun]

relatively recently i found an 800xl in MY town on facebook, and i was thrilled to get into it for the first time. it was really unexpected, but i like this computer a lot. ran into problems with mine after doing some mod work to it but other than that worked well. this videos certainly gonna help me out troubleshooting it when i get around to working on it again Also, im sure someones mentioned it by now but, for the chroma mod, ive seen people suggest a 300 or 330 ohm resistor to the chroma pin rather than a straight connection, might be the cause of the strange blown out color fading down to normal. im personally not sure but its what people usually do.

[@Augustus087]

Wow, look forward to this. I happen to have an Atari 1040 St that needs some repairs as well.

[@mondovicium]

Back in the day, I had a 256K upgrade for my 800XL. As I recall, I had to solder 256Kx1 chips on top of the existing ones, except for the chip select pins which went to a new board. It may have also replaced the ANTIC chip, but that I'm less certain of. I may be confusing it with a later mod to my 130XE to give it a 65816 chip. Bothe upgrades worked great until the computers eventually died, and repairs were well beyond my skills.

[@jimsteele9261]

Back in those same days, I did a 256K upgrade to my 800XL also. I can't remember if the RAM was socketed and the 256K chips replaced them or were soldered over... In any case, some wires came over from POKEY I think to drive some of the address lines. I think it bank switched it in 16K chunks. A modified DOS treated the extra RAM as disk drives.

[@mondovicium]

@@jimsteele9261 My RAM was socketed, but the new RAM had to soldered onto the old RAM, pin by pin, with the exception of the chip select, then the combination reinserted. Right, it had to be bank selected in, possibly in the space where the non-existent second cartridge slot would have been. Pretty much the same as the extra memory in the 130XE.

[@kumarp3074]

I purchased an 800 XL a while back through an auction to play my old games. I used to own an Atari 400 when it was first released and even though I got rid of the machine, I still had all of the cartridges. I'll be sure to refer to this video if my 800 XL stops working.

[@psccomputersmissouri]

Excellent job Adrian! Love the 800XL and the Luma/Chroma rocks

[@Stratotank3r]

Nice Job! At 4:03 when you tilt the system to show the cpu the antic chip looks very suspicious. Small cracks and bulges. Would be interesting to tests that thing somehow or grind it down to see the inside...

[@russellhltn1396]

I saw the same thing. It was bubbling up from inside. A sure sign of a chip that's gone nuclear.

[@muttBunch]

I love the 800xl yay ❤

[@angrydove4067]

Good show, I look fwd to more 8 bit Atari repairs. The 600XL was my first computer too, back in 1985.

[@farmersteve129]

The schematics are useful as a guide, but watch out as there were multiple revisions (aside from the variations for PAL, SECAM, NTSC, etc) & some of the later units were significantly different to the earlier ones - particularly with the inclusion of the Freddie multiplexer chip.

[@Drew-Dastardly]

I noticed visible defects with that ANTIC chip and suspected it right away especially with the heat. Now one complete total bodge hack is something I have seen work to revive old game ROM cartridges. It is totally disgusting but you can fit a 5V pull-up resistor to the bad lines and it gets these old chips going again. I would totally heatsink that chip too. It may be worth doing just for science. ;)

[@danielmantione]

If the A13/A14 is the only defect in the ANTIC that may work, but if it is hot, then likely it is significantly damaged and won't be able to run an old game.

[@Drew-Dastardly]

@@danielmantione Yes it is a vile hack and purely for science. I would be happy to run a system for short periods with an unobtanium chip for example. I would never sell it on to an unsuspecting customer.

[@ldlm91]

This was my first computer. I believe my uncle still has it!

[@railsrust]

27:13 FYI, the POKEY sound chip is a little different than what you think. It has four voices that can either be a square wave OR noise. There's some other funkyness you can get away with on the square waves, but that's generally what you have. Not quite as sophisticated as a SID chip, but much better than the SN76489 from TI, and has an advantage over the AY-3-89XX chips due to having four voices rather than just three. The music for the POKEY is actually pretty good. I know there is more to the POKEY than I mentioned, but I'm trying to keep things simplistic.

[@moforetro3612]

the pokey is one of the most beutiful sound chips if used in the right way. it sounds very pure.

[@PlumGurly]

Yes, you can do neat things with it such as bit-bang it directly or put it in 16-bit mode. That ties up 2 ports, so you only can have 2 sounds, or 3 if you mix and match.

[@nickolasgaspar9660]

Way to simplistic to make this comment informative . POKEY has 4 independent 8-bit frequency divider channels. Merging channels together brings the new one up to 16bit . That can be done on the fly during a playback. The waveforms produced by Pokey are square (rectangular) and triangle or sawtooth (through programming the chip itself(distortions)). It also has High Pass filter. According to Jay Miner talks Pokey was a hybrid synthesizer with PCM capabilities(later found in Paula). Those capabilities were enabled by the A8 architecture and especially by the increased frequency of the CPU(In Amiga Agnus addressed that). This means that rendered samples (Soft Synth or Digital samples) are fed by the CPU in small packets per cycle allowing the reproduction of sampled tracks of PWM without affecting the speed of the graphics on screen(Reharden as an example). This allows games i.e. Space Harrier to have digital samples while rendering the playfield and sprites without any slowdowns. This also allows in modern Cartridges solutions to have video playback with full 256 colors and PCM sound. Many think that the SID was the more modern and innovative chip, but in reality Pokey showed the future of sound in the industry which didn't include synthesizer chips. SID was the best Synth chip ever used in a home computer, but it was just that. A cut down Roland chip with amazing capabilities and with a expiration date for all synth chips. The problem is that SID's sound is shared by many synth keyboards of the era...which unfortunately they were also widely used in porn industry(soundtracks). The only down side of the Hybrid nature of Pokey is, because of its PCM and PWM abilities of the architecture , features (i.e. Low Pass Filter etc) were dropped during the process of production to cut cost. Now those two chips have a different "metal" in the sound they produce, so what we get are better or worst performance in different types of music.

[@JamieStuff]

IC test clips are still being made. They are considered specialty items these days, and are priced accordingly. There has been some work on an FPGA replacement for the ANTIC, called "Fx ANTIC". The source has supposedly been released, tho I haven't been able to find it.

[@ovalteen4404]

Yep, Mouser has them for an average of >$100 each.

[@simontay4851]

Over $100 each! Fk me! Thats insane.

[@tmwinkler]

OMG! DipClips! You are so old-school! (As am I.) Thanks for sharing maestro!

[@marcinmiklaszewski9336]

If i recall correctly the circuit for that color potentiometer use phi1 just as a alternating voltage source to generate "high" voltage, higher then 5v. If you'd probe the potentiometer leg you should see it is completely fiłtered DC. Nice troubleshooting! PAL ataris have very noisy 5V, looks like it here too. It helped mine to directly bypass power on Freddy chip (next to Antic) under the board with 100n capacitor to improve the video while having the composite still connected. And one of my 800xl had luma/chroma output out of the box and it was the older one, without Freddy. All the best!

[@zero0ryn]

Nice one Adrian. Good to see some 8 bit Atari goodness on the channel :)

[@ruthlessadmin]

WTH? I've heard of people getting unsubsribed from channels but never experienced it until now. Usually only affects political channels too. Resubscribed!!

[@gamedoutgamer]

Well done Adrian. Your technical electronics knowledge is great. Antic is supposed to run quite cool. It varies some but I've never seen Antic run hot. Your using the schematics is very informative and welcome. It's an established practice to replace the custom chips one at a time to diagnose and repair these. The chip may have been fried by a failing ingot PSU. The lower half of the case looks like it was dunked in a chemical bath to brighten it and in the process the texture was eaten away...? 13:50 the only chip that I know that can be removed and not halt operation of the computer is BASIC ROM. Maybe the tiny audio amplifier chip can likely be removed and it will still operate. It's recommended to use composite for when the machine uses color artifacting but nowadays many people use chroma+luma for the increased clarity. The hottest chip is usually GTIA followed by the CPU. All other chips from my experience run warm to near room temperature. I think the reason they didn't include chroma line on most 800XL's is because there were almost no monitors that used it when it was being designed. The worst aspect of the design of the 800XL motherboard is probably the video circuit. It's a great overall design and improvement over the 1200XL but the 800XL is a cost reduction. However nowadays the 1200XL is more revered in the community because its overall build quality is better and for its aesthetics. The 800XL is however a better product as far as bug fixes and as an actual final finished computer worthy of release.

[@felixcosty]

Thanks for the video. I miss my 800xl and one specific cartridge game, it was maze game, you would go from room to room till you found the next level. Wish I could remember the game.

[@TonyAtkinspdx]

I love the looks of the 800 XL

[@TheBitPunch]

Thanks for the Saturday video, Adrian! It’s a good morning now.

[@CalculatorObsessed]

Hope you can source a suitable replacement chip, so it’s not an either or situation. Good call on heat sink for those with working ANTIC chips.

[@gamedoutgamer]

Thankfully Antic chips are cheap and available still today. New old stock unused ones even.

[@twocvbloke]

That dead chip looked like it had some bulging from overheating & burning itself out internally, sometimes a visual inspection under magnification can speed things up when you spot such issues... :)

[@K-o-R]

A quick google suggests that, in the UK at least, those chip clips are readily available for all sorts of packages.

[@firstsurname9893]

Yep, Warwick Test Supplies in Southampton have a large range and also ship to the US and Europe. I think they're starting to disappear in North America because 3M appears to have stopped making them.

[@gregsgeekery]

I was working on my 800XL when I saw this video so I decided to go ahead make the video mods. My unit actually DID have the C56 capacitor. I posted a video (kzbin.info/www/bejne/o3y8gH-KpslkqLM) of the my work session and you can see a closeup of the improvement of removing C56 at time=~13:00, and closeup of Composite vs. S-Video at time=~27:00

[@chad2787]

I vaguely recall these antic chips being known for running warm. I had an original 800 that would bug out after a few hours (picture would go to snow, even though it was a monitor) and had to cool down for an hour or so before it would work again and being told at that time it was probably this chip. There were no parts or eBay then and these machines were outdated so I passed it down and moved on to a 286.

[@grakkal]

I'm a simple man. I see an Atari 800XL, I click, and I watch.

[@RudysRetroIntel]

Great repair work! Thanks for sharing

[@danielmantione]

Huge memory expansions on the 800XL don't extend the bank switching inside the machine. The PBI port of the Atari XL machines allows PBI expansions to disable the internal RAM and get chipselect for the RAM (which is CAS) on the PBI port. Therefore you can replace the RAM with external RAM, and if you implement some bank switching logic on the expansion card, you can give the little Atari XL access to a lot of memory.

[@jasonmoore1051]

Hi Adrian! Love all your videos. I am particularly interested in Atari 8-bit repairs as I run the Atari Projects website. I would be really interested in a video on repairing an ATR8000 for the Atari. Thanks, and keep up the awesome, insightful, and education work!

[@AsmodeusMictian]

Holy smokes......well there's a few months of my childhood returned. Thanks! :D

[@DManSKIDROW]

Great Video. Will b Using It As A Point o/Reference.

[@HuntersMoon78]

800XL is a nice looking machine.

[@perinoid]

First, there's an oscillator. It generates a signal that is fed into GTIA chip. GTIA generates another clock, then goes into Antic, which generates Phi0. The Phi0 is buffered and delivered to the CPU as Phi0. Sally generates Phi1 and Phi2. Phi1 is used for color phase. Phi2 is then distributed over all other big chips (including Antic and GTIA again) and memory system (it's buffered for majority of these). If you'd wanted to disassemble this type of keyboard, don't try to open the switches. There's a film on YT which shows how to properly do it. It's a bit complicated.

[@PG-gs5vb]

The POKEY has 4 channels. One extra channel is provided by GTIA and is used for the keyboard clicks. It's just a 1-bit beeper-like output.

[@johnhunt1725]

It's the HALT pin that is unique to the 6502C "Sally" chip. The system uses this to suspend the CPU while the ANTIC chip utilizes the system bus to do its "primitive GPU" thing.

[@danielmantione]

One thing that I never understoond is why the RDY pin is avaiable on the PBI port instead of the HALT pin. RDY on the PBI port is quite useless, yes you can halt the CPU that way, but the address bus remains active, so you cannot do any DMA like the C64 can (in the C64 the DMA pin activates both RDY and AEC). If the HALT pin would have been on the PBI port, Atari PBI expansions could do time like is possible on the C64.

[@gryzman]

doing memory expansion would be great, and seeing if there are any antic chip alternatives nowadays

[@PlumGurly]

Yes, that capacitor is there to help reduce jail bars, but it can cause blurring too.

[@jandjrandr]

Still think it is funny I was never exposed to an Atari computer growing up. Did see any in the stores I went to as a child, yet there were so many other computers available.

[@RixtronixLAB]

Nice video, well done, thank you for sharing it with us :)

[@AntneeUK]

Looking at the R38 potentiometer: "This may potentially adjust..." Yes, that's what potentiometers do 😉

[@RemcovanZuijlen]

I was looking for this comment.

[@cbmeeks]

I did the s-video mod and it was great. Then I installed a Sophia 2 and never looked back. 😀

[@oubliette862]

This reminds me of 8th grade computer class. The computers were apple 2 green screen things. I must say I hated that class and those computers so much that I didn't want nothing to do with a computer of any kind until about 2006. I'm over it I like computers now.

[@BartManNL]

The yellowing is (at least) partially caused by brominecompunds that were added to the material to fireproof it. It seems that the bottom shell is of a different material where the bromine seeps out easier.

[@gilbert1975nf]

04:00 - Well well well We can see right here that appears to be some damage in this antic chip, right there on it's enclosure! Perhaps somebody had worked here before you Adrian?

[@anthonydenn4345]

Nice job Adrian. Would be nice to see a quick game or software running on it. Never had one of these bitd, it looks interesting. Not a bad looking keyboard either. Ok just watched it again, missed the Ms Pacman game, cool 😉

[@retropuffer2986]

Have you repaired Atari today?!! 🎶

[@winstonsmith478]

You should buy or ask for one of these thermal camera attachments for your phone as used here: Bendix Air Data Computer - Part 3: Magnetic Amplifier Magic kzbin.info/www/bejne/bp_LY2mih9KFmrM

[@MD4564]

Hopefully antic and other chips can be replicated at some point.

[@7alken]

my high school workhorse )) great repair ...

[@shmehfleh3115]

I have a couple of 800XLs and an XEGS. I'll have to try that s-video mod on them.

[@pupaepedorra]

The video was nice, but i want to see it fully buffed up!

[@shawnj4545]

The 6502C has the HALT signal that allows the CPU to be halted temporarily so that ANTIC can take over the bus for generating the display. The built-in memory test does not test the memory under the OS ROM, and from all accounts it's not a very good memory test. You see 48 squares with BASIC disabled. If you have BASIC enabled and drop to the self-test by typing "BYE" you will see less squares, since some address space is being taken up by the BASIC ROM. The 130XE implemented bank switching for more memory using the PIA Port B, and ram upgrade makers used that standard for creating memory upgrades for the 800XL (actually it could be that third party memory upgrades existed for the 800XL before the 130XE and Atari just stole the idea after the fact). Initially Atari only used port B for enabling the RAM under the OS, and switching internal BASIC on and off, so there was unused bits available. One really interesting thing that the 130XE added, via an upgraded MMU (I believe) was separate memory bank access for the CPU and ANTIC, so you could have ANTIC working on an extended memory bank and the CPU accessing a different memory bank. Cool feature, but not well used since only the 130XE supported it. I'd like to see you work on more Atari 8-bit computers! While not sporting the graphics capability of the C64, arguably, they had features that were well ahead of their time. The ANTIC chip being a processer in it's own right, complete with it's own opcodes allows for some very cool effects and video display manipulation. The SIO/CIO system that supports loadable device handlers, the Parallel Bus Interface that gave us hard drives and other advanced peripherals on the Atari 8-bit. SpartaDOS, a powerful CLI DOS that almost everyone with a hard drive was using BITD (and now too). So many cool features, although most people just played games on them. :)

[@TzOk]

MMU, was the same, there was one extra chip, sometimes referred as EMMU to deal with that Antic memory access. By the way - MMU is not a fully custom chip - it is a PAL16L8, and can be replaced by GAL16V8.

[@thisnthat3530]

the 800XL can independently switch the RAM bank under the ROMs between the CPU, ANTIC, both or neither. There is a separate bit to switch for each. The 130XE RAM banking can also be reproduced by cutting a couple of tracks, piggy backing another 64K of RAM and wiring in a few TTL logic chips rather than utilising a GAL. 7400 series ICs are easier to obtain.

[@belzebub16]

Good job! 👍

[@GarthBeagle]

Another one saved!

[@RyeOnHam]

18:05 -- okay, does anybody else see Homer Simpson in that adjuster? He's sideways.

[@PlumGurly]

Actually, the issue with ANTIC is that it is your bus master, and I think Freddy/MMU asks it to pause the CPU so it can refresh the RAM. As for the CPU staying high after bending the pins, it could be that since ANTIC is not working, it is not throwing raster and frame interrupts. I don't know if that affects the ROM routines or what. It is purple because you need to adjust a pot on the board. They put that there since changing boards/chips can draw different amounts of current and affect the colors.

[@cbmeeks]

If you're unsure a vintage, custom chip is working or not, I don't think I would recommend cutting pins on it to debug. lol

[@Rorschach1024]

Those clips were made by OK Industries, ITT Pomona and others.

[@tuomollo]

The main difference between a regular 6502 and 6502C is the presence of the HLT signal that halts the CPU when ANTIC wants to access the memory.

[@kirusyaga]

There's a FX Antic - FPGA replacement for ANTIC. So it's not an end for this 800XL.

[@Cash2024]

My 1st computer ❤❤❤❤❤

[@moshly64]

Apparently that chip is available from Best electronics ca for $5

[@paveljelinek772]

Antic is caput.. it's clearly shorting those adress lines and so it gets more amps, that would explain the hot..

[@stephenkrzanowski]

@3:59 I'd say a visual inspection of the board showed that bad antic chip right away. Cracked & bulged surface there...

[@TzOk]

The Chroma signal level is wrong for S-Video in all 8-bit Ataris. The S-Video standard went later, and Ataris are compatible with some old Commodore monitor. I can recommend Atari Simple XE Video output mod by TheRetroChannel.

[@michaelstoliker971]

Wow, you found a broken 800XL, how rare!

[@jagmarc]

I used to repair 100s these in the 80s for a consumer electronics distribution centre. I can't remember any the faults. edit remeber RAM chip faults common , find the bad one by piggybacking over top each one with good ones , then flicking them off one at a time until crashed. and the other fail mode find the bad one by spraying all of them freezer spray then the one that defrosts first is the bad one

[@giulianomarco]

😁👍

[@mariestarlight]

I always watch you using that nintendo controller for your atari, etc. Did you know that you could plug an unmodified sega genesis controller into an atari 2600 (and maybe later if it's the same port) and it just works like a joystick. The middle button (b) becomes the 1 button that would have been on the joystick. As a kid having both systems, I tried this randomly because I hated how hard the joysticks on the atari were to use, and the ports were the same size. Surprised me that it worked, but made so many atari games easier to play.

[@ChrisHopkinsBass]

I think someone fitted a replacement bottom panel, hence the different levels of yellowing on the two pieces

[@rickhunt3183]

Personally I would have inspected the traces on both sides of the board first thing. This old stuff is so easy, If you're going to working with old stuff, you should put together a board you can plug the cpu's into with some rom and simple I/o so you can observe the input/output signals from the device and verify operation. I'd use a 555 to slow things way down and be able to single step the device if necessary. A simple logic probe can give you a lot of information quickly. Also ic test clips are still available through a lot of different outlets including amazon. Maybe you should consider building your own version of this computer minus the custom chips if you're this passionate about 6502 based machines. One interesting thing to note is the people who designed and built this computer were probably high at the time. I don't know if that's a testament as to how good the engineers were or how simple these computers are or both.... Now back to the video.

[@another3997]

Considering Jay Miner and Co went on to design what eventually became the legendary Commodore Amiga, I'd say they were great engineers. They designed the original Atari 400/800 machines, which were released in 1979, and were cutting edge in terms of graphics and sound. For comparison, the C64 came out in 1982, and was only marginally more capable, despite being 3 years newer. Cue hordes of C64 fanatics frothing at the mouth... 😂

[@rickhunt3183]

I dont know who built the amiga 500 but that machine with the mc68000 was real power. I haven't written any code for the 68000 in long time. I was thinking about trying to find an amiga 500. Assembly language is dead, but us old people still find it interesting. The late 70s and early 80s was a whole different world. I should have taken a job with Atari. Those were some party people, but later I was with a group from IBM working in boca raton. A lot of wild things went on there. Probably as wild or wilder than at Atari. Originally the PC almost had a 68000 cpu, but there was lots of confusion and party supplies at the time Motorola was visiting. No one was formally in charge that week. Maybe someone will write a book one day or maybe not. Somethings that happened there at work shouldn't be told. We didn't party after work. We were always working, and were always partying. Those were different times. Anyway. It's well past my bedtime. Thank you for the interaction. I hope you have a great night.