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Unadentified Switch (mod or official?)


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My current Atari 8-bit computer of choice, an 800 that I rebuilt from rather poor condition to new like condition, thanks to being able to get parts from Best Electronics, has a little mystery, or at least what is a mystery to me. I currently haven't seen anything like this before. It is a little metal on and off switch, attached to the bottom of the machine and soldered into the main board. When I had this system apart, I could identify no sign of modding and to my knowledge, this computer sat in storage since the 80's until I acquired it, so most likely if this switch is not official added by Atari for some reason, then it most likely is a really well done mod job by someone in the eighties.


Here's a shot of the computer when I acquired (taken by the seller,) it along with several games, a bunch of joysticks and a non-working 410 for around $30. The important parts, the insides were in beautiful shape, everything else was either repairable, washable or replaceable. So I think I got a pretty decent deal.



Here is a picture I took of the computer running not long after I finished refurbishing it. On a side note, the game, Transylvania, is running off the official disk from my purchase of the game in 1985. Considering that I found this disk loose from years of storage, it's fascinating that it still works well. Even though I do have a usb SIO2PC module, I cannot see any real reason to back this up since it is already backed up on the internet.



Here you can see the mystery switch on the bottom of the computer. I've tested it with my multimeter to make sure I knew which way was off and have left it there since I don't know what this switch does.



Here is a picture of where the switch is attached to the bottom of the main PCB.



I have looked at lots of picture of other 800s and can find no picture of anything like this. Also the memory boards in my computer are all untouched gold fingered 16k memory boards enclosed in the metal cases. If any internal boards where replaced with a third party board inside the machine, I am not familiar enough with it to recognize that it had been changed. I have speculated that maybe this was some kind of Mosaic mod or some other memory mod but can find nothing to confirm it. Anyone has any ideas what this switch does, I'd greatly appreciate the help. Thanks.

Edited by KBRpilot
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Quick & dirty guesses - I don't have an 800 so can't trace from that point to see what it's attached to.


- write protect for cartridge Ram area. If this is the case it would allow running copied 8 and maybe 16K nonbanked cartridges without need to remove copy protection code.

A quick test would be, insert Basic. Flick the switch and see if you can still type on the screen.

Type ? FRE(0)

If the Ram amount is the same from each initial position and your typing still appears onscreen then probably not a 16K Ram protect switch.


- enable for second Pokey. If this is the case then try from both initial switch positions:

SOUND 0,200,10,10

POKE 53777,0

If the sound doesn't stop then you've got a stereo Pokey setup. Though these are usually installed such that seperate audio from each one can be tapped e.g. 3.5mm jack or 2xRCA plugs.



ed - actually, that looks like the power supply board, not the mainboard. Looking further, after searching for other 800 board pictures, my conclusion:


Override for cartridge door switch. Try opening the cartridge door with switch in each position. Likely that one position will keep the machine powered on.

Purpose for this could be to aid with copying carts.

Edited by Rybags
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@ Dragonstomper, I have tried with Best, but didn't get a response, quite possible the photos got me caught in their anti spammer.


@ Quadrunner, I'll give those suggestions a try. They're good ideas. Come to think of it, it is on the power board, directly in from where the AV port is. So your last suggestion might be right. I've been doing a lot of early CRPG gaming on it a lot late at night. When I set up tonight, I'll check that out.

Edited by KBRpilot
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That is an override switch for the cartridge door. Easy way to tell is open the lid with the switch in one position and see if the computer powers off, flip switch (with lid still open) and see if computer powers on.

I am certain that is what it is by looking at the connection points in your pictures. I normally make a permanent bridge across those connections because the lid switch is annoying, especially if you use tall carts.

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Thanks for the suggestion. You guys are exactly right, it is a bypass for to off switch when the cartridge door is open. That will actually come in pretty handy because I'd like to play around some day with some of the newer flash memory cartridges. I had been wondering How I would do it since I didn't want to permanently hard wire it to think the door was always closed as I like using it as a hard reset when loading different disks (it's easier than reaching around to the power switch.) The switch is a nice way to have both. Back when I first tried the switch to see what it did, but hadn't thought of trying the door.

Edited by KBRpilot
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Although the function and placement would be different, I've got a similar switch on one of my 800s. It sends power to the cart, on off. Super neat, just hit reset after the switch and what ever cart is there powers up with out having to open the door at all OR the cart is gone like magic. I like it.


Like Kyle22 suggests, if I did anything in there myself, it would be to kill that door switch permanent like.

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