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Just bought an 800xl - What is this mod?

800xl mod newbie

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#1 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 5:33 AM

Hi, I'm new to Atari 8 bit computers having grown up with C64 and Spectrums. I recently bought a bargain 800XL from eBay (yes, miracles do sometimes happen). I don't have any software yet but I was able to get the machine into self test mode (what a cool feature!) and it passes just fine.

 

There seems to be some after-market mod on the system, can anyone tell me what it's for? Here's a picture of it:-

 

32196087342_dfb6ae164f.jpgIMG_0922 by videogameperfection, on Flickr

 

There's three switches at the back. I tried flipping them but all that seems to happen is the machine boots to a blank screen.

 

Does anyone have any idea what this might be? My intention with the machine is to RGB mod it using Lotharek's VBXE board and probably add a flash cart of some description too. Hopefully whatever this is won't interfere with that!

 

Thanks in advance for any help



#2 Gunstar OFFLINE  

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Posted Tue Jan 17, 2017 10:05 AM

Well, Atari computers with built-in BASIC have BASIC on by default and it has to be turned off while booting by holding down the OPTION key to load non-basic software (auto load thank God, none of that typing in like on the C64). 

 

The middle switch I'll let someone else take a crack at, even though I think I know, but not sure (OK, my guess is alternate ram and OS configuration).

 

The last switch could be a lock out for power or something else, not sure really.


Edited by Gunstar, Tue Jan 17, 2017 10:07 AM.


#3 mytek OFFLINE  

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Posted Tue Jan 17, 2017 10:11 AM

Be really helpful if we could see what it looks like inside  ;)

 

- Michael



#4 Dropcheck OFFLINE  

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Posted Tue Jan 17, 2017 10:15 AM

It's best when you first get something like this that has been modded, that you open it up and check for loose connections/chips.  About half the time any problems you have are caused by that.  The other half the time is that it's not malfunctioning you just know what it's supposed to be doing, so you think it's bad. :grin:

 

Of course the other half the time there is something wrong.  :(



#5 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 11:30 AM

All right, lets go exploring! So first of all lifting the lid on the Atari

 

32219344902_d6f759ebd4.jpgIMG_1243 by videogameperfection, on Flickr

 

Well that  doesn't show us much, guess we need to get that circuit shield lifted. I didn't realise the power LED was an after-market mod, that made dismantling the unit a bit harder since it couldn't be disconnected without resoldering and I suck at soldering. Anyway, after slicing my finger on the circuit shield (hope I wont need a tetanus shot) I got the thing disassembled.

 

32330482276_cb9fa1e978.jpgIMG_1244 by videogameperfection, on Flickr

 

(sorry the picture's a bit dark). So it looks like this expansion board fits on the sockets on the motherboard there. I didn't think I managed to pull it out of the socket taking the computer to bits but I couldn't swear to it actually on further inspection it doesn't seem to sit in the socket all that securely, so I could definitely have pulled it out without realising. I don't see any markings on the little PCB indicating manufacturer etc. There's also one wire that goes to a leg on this chip.

 

32219344752_5b9d5a81b3.jpgIMG_1245 by videogameperfection, on Flickr

 

 

Here's one closer up with better lighting, you can see the numbers on the chips. Oddly it looks like the numbers on some of them have been deliberately removed:-

 

31558645573_d291b9eac5.jpgIMG_1246 by videogameperfection, on Flickr

 

So, anyone any clue what this is? :)


Edited by BuckoA51, Tue Jan 17, 2017 11:34 AM.


#6 Mclaneinc ONLINE  

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Posted Tue Jan 17, 2017 11:42 AM

I can't say what they are but I'd suggest a bit of tape or a plastic cover on the switches, I had a custom 3 OS system made for me back in the day and I managed the Omnimon board with static conducted down the switch..(no diodes)



#7 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 1:30 PM

Got her back together but managed to break the wire to the green LED that had been added on top of the computer after all. It really was very short so I guess it was inevitable especially for someone clumsy like me (this is why I have subcontractors for soldering/modding work :)

 

Still very much in the dark as to what this thing is. Looking at the 800XL motherboard it seems to fit in where the MMU normally lives, so some sort of RAM upgrade?



#8 mytek OFFLINE  

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Posted Tue Jan 17, 2017 1:50 PM

I don't know exactly what it is, but it definitely appears to be associated with the address decoding since the MMU and the 74LS138 play a big role in that (the marked chips). The unmarked chips are not large enough to be DRAMS, so not sure what this is all about.

 

Does it still have the original OS ROM and Basic ROM chips on the motherboard?

 

- Michael


Edited by mytekcontrols, Tue Jan 17, 2017 1:52 PM.


#9 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 2:12 PM

Well they don't seem to be missing but I'm not sure how I could tell if they were original?

 

If I wanted to return the machine to stock could I just lift those two chips off the expansion board and put them back in those two sockets?



#10 tep392 OFFLINE  

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Posted Tue Jan 17, 2017 2:16 PM

The BASIC toggle probably just toggles BASIC on/off.  If you boot with it on, you should get a READY prompt.  With it off you will get the self test.  That is if you have the Atari OS selected.

 

I'm guessing the center switch selects Atari OS, Alternate OS and No OS.  The alternate OS could provide faster disk access if you have an upgraded drive.  Or monitor program for debugging.  Could be a lot of things. Try it out and see what you get.  The RAM position might disable the OS completely which would give you access to the RAM underneath the OS.

 

Don't know what the lock does.  

 

Is there anything written on the front or back of that circuit?



#11 tep392 OFFLINE  

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Posted Tue Jan 17, 2017 2:22 PM

Take a picture of the chips to the right of the cartridge slot.  Those are the BASIC and OS ROMS.



#12 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 2:23 PM

The BASIC toggle probably just toggles BASIC on/off.  If you boot with it on, you should get a READY prompt.  With it off you will get the self test.  That is if you have the Atari OS selected.

 

Yeah this seems to be what I'm seeing.

 

I'm guessing the center switch selects Atari OS, Alternate OS and No OS.

 

That seems likely. Setting it to either the first or second position makes the machine boot basic or self test (depending on the BASIC switch). Setting it to the third position (RAM) just gives a green screen, because I guess there's no OS in RAM

 

Take a picture of the chips to the right of the cartridge slot.  Those are the BASIC and OS ROMS.

 

Aww snap I only just put it back together :)



#13 mytek OFFLINE  

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Posted Tue Jan 17, 2017 2:25 PM

Well they don't seem to be missing but I'm not sure how I could tell if they were original?

 

If I wanted to return the machine to stock could I just lift those two chips off the expansion board and put them back in those two sockets?

 

The ROMS would most likely have the Atari name on them.

 

star-arabic-atari-65xe-inside-view-06-sm

 

Whereas an after market replacement wouldn't (and it would probably be an EPROM with an erase window on top). So if this was some kind OS switch it should have a custom ROM.

 

Yeah I would think simply plugging the LS138 and the MMu back in without the board would get you back to square one  :)

 

- Michael



#14 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 2:40 PM

If they've been replaced it's a neat job, these look like the originals...

 

32222401352_027b04e6fa.jpgIMG_1249 by videogameperfection, on Flickr

 

Here's the whole motherboard, for interest:-

 

32372712035_511ba58fab.jpgIMG_1248 by videogameperfection, on Flickr

 

Yeah I would think simply plugging the LS138 and the MMu back in without the board would get you back to square one  :)

 

Maybe I should do that then and just cut off the wires. I suspect whatever mod this was is now obsolete anyway once I've added a VBXL and some kind of flashcart? Then again I don't want to destroy it if it's useful/of interest to anyone. Quite happy to pick up another 800XL on eBay and part with this one if it's in some way unusual/useful to anyone?

 

Appreciate all the help anyway!



#15 mytek OFFLINE  

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Posted Tue Jan 17, 2017 2:47 PM

Yep stock Atari ROMs, no multiple OS possible via that route. I keep wondering what that 20 pin green socket was for ? Maybe some kind of SRAM or FLASH ROM chip, but I don't recall something with that small of a footprint. I'll have to look.

 

- Michael


Edited by mytekcontrols, Tue Jan 17, 2017 2:51 PM.


#16 gozar OFFLINE  

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Posted Tue Jan 17, 2017 2:52 PM

Yep stock Atari ROMs, no multiple OS possible via that route. I keep wondering what that 20 pin green socket was for ? Maybe some kind of SRAM or FLASH ROM chip, but I don't recall something with that small of a footprint. I'll have to look.

 

- Michael

 

Static ram chip/No OS/Lock, could be some way to play copied cartridges. Load the cartridge into SRAM, lock the SRAM, then boot the machine.



#17 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 2:57 PM

Oh, well that's definitely not something I need if I'm going the flashcart route anyway?



#18 mytek OFFLINE  

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Posted Tue Jan 17, 2017 2:59 PM

 

Static ram chip/No OS/Lock, could be some way to play copied cartridges. Load the cartridge into SRAM, lock the SRAM, then boot the machine.

 

Problem is I'm not seeing any 20 pin skinny-DIP packaged RAM or FLASH chips that would yield that much memory. But I do see a lot of microcontroller chips being offered in this package size. Hmm... I wonder.

 

- Michael



#19 tep392 OFFLINE  

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Posted Tue Jan 17, 2017 3:07 PM

Can you get any numbers off those chips that were sanded?  The only reason someone would do that is to make the design harder to copy.  This might have been a homebrew project that someone was selling back in the day.  Very interesting.



#20 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 3:27 PM

I can make out maybe 288..on the bottom chip.. top one looks like it might  have been an S?

 

31562312613_0c86a929fc.jpgatari-chips-zoomed by videogameperfection, on Flickr

 

I'd be happy to trade this machine for a stock 800XL if it really is interesting to anyone.



#21 kheller2 OFFLINE  

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Posted Tue Jan 17, 2017 4:30 PM

Maybe you could copy the OS to the RAM under the OS, modify it and LOCK it, then do a reboot (somehow) and boot off of that by toggling the OS switch.



#22 Kyle22 OFFLINE  

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Posted Tue Jan 17, 2017 4:54 PM

I can make out maybe 288..on the bottom chip.. top one looks like it might  have been an S?

 

31562312613_0c86a929fc.jpgatari-chips-zoomed by videogameperfection, on Flickr

 

I'd be happy to trade this machine for a stock 800XL if it really is interesting to anyone.

Spit on your finger and touch the chip.  Sometimes this will bring out the numbers if they haven't been too deeply ground off.



#23 BuckoA51 OFFLINE  

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Posted Tue Jan 17, 2017 5:05 PM

I've had to shelve this for a day or two to work on other projects but I'll give that a go and report back.



#24 sup8pdct OFFLINE  

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Posted Wed Jan 18, 2017 1:20 AM

Re that chip socket. I would say they used a socket with extended pins as it was easier to get then a header.

 

James



#25 re-atari OFFLINE  

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Posted Fri Jan 27, 2017 6:55 PM

Hi, I'm new to Atari 8 bit computers having grown up with C64 and Spectrums. I recently bought a bargain 800XL from eBay (yes, miracles do sometimes happen). I don't have any software yet but I was able to get the machine into self test mode (what a cool feature!) and it passes just fine.

 

There seems to be some after-market mod on the system, can anyone tell me what it's for?


There's three switches at the back. I tried flipping them but all that seems to happen is the machine boots to a blank screen.

 

Does anyone have any idea what this might be?

There's an earlier thread on AA about an 800XL with this upgrade. Difference with your XL is that it also had its OS replaced with an eprom, and that the CO61618 MMU was placed in the other socket (the empty one on your PCB).

 

A sticker on top of the eprom said 'XOS The Tool'. The firmware contains the string 'Super Chip! © 1986 Computer Support UK LTD', so it's safe to say it's an UK upgrade, probably intended for making disk/cartridge/tape backups. No idea if this firmware is in any way related to the extra hardware on the plug-in PCB. As your XL contains the standard XL OS rom, it appears the PCB doesn't require the custom firmware to run. Vice versa may be another story, though.

 

edit: just did a quick search for XOS, and found the thread I mentioned:

http://atariage.com/...s-than-answers/

 

and another edit: reading the above thread it appears the other 800XL didn't have its OS replaced, but an eprom containing the custom firmware added by piggybacking.

 

re-atari


Edited by re-atari, Fri Jan 27, 2017 7:05 PM.






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