help with 800xl please

[mimo]

got a ntsc 800xl.

power light comes on, but no video output.

will not boot to self test

tried a miner 2049er cart, got a brief flash of a green screen, then back to no video output(black screen), got some audio hiss though.

 

any pointers welcome!

[Urchlay]

By "no video output", do you mean nothing at all (TV displays static or bluescreen with "no signal"), or is it a solid black screen? You said you got a flash of green and some audio hiss with a cart in... so probably the board is getting power and the RF modulator at least works (or are you using composite/s-video output?)

 

If it's solid black, the most likely candidate is one or more dead RAM chips. Also one or more of the other ICs could be dead (POKEY, ANTIC, PIA, etc).

 

First thing to check is the power supply. You can find the pinout in the Atari 8-bit FAQ... if you check the voltage with no load, it'll be more than 5 volts. Make sure the polarity is correct: I've had a failed power supply that put out -2 volts (2 volts with backwards polarity).

 

Your best bet is going to be to get a working 800XL, and swap chips with the dead one, one chip at a time, until the working one stops working. At that point, the dead one may start working (means only that one chip is bad), or both may be dead now (means something else is bad, keep swapping chips). With lots of luck, both 800XLs may have socketed chips... otherwise, you'll end up doing a lot of desoldering, and if you don't know what you're doing, it's possibly that you could fry a good chip trying to desolder it.

 

In your other post, you describe a working 1200XL (except for the keyboard)... Most of the chips in the 1200XL are the same as the 800XL, so you may be able to do the chip-swap thing with the 1200XL and 800XL, instead of buying another 800XL.

 

If the culprit turns out to be bad RAM, or one of the "little" ICs like a 74LS158 or such, these are still off-the-shelf parts you can buy from Mauser/Digikey/etc. If you've got a bad custom chip, you'll have to pull a replacement from another Atari (600XLs make great donor machines), or ask on this forum if anyone's got spare parts. Actually, I'll have a few spare ICs in the near future: someone was kind enough to send me most of the chips from a 600XL, so I can fix my 800XL... when I eventually have time to fix the 800XL, I should have a leftover 6502, ANTIC, POKEY, and possibly a GTIA (not sure if mine is bad or not). I'm willing to pass them on to someone who needs them...

[mimo]

Thanks, looks like a lot of work, but it is a nice clean machine, and worth saving.

I am using composite out as I cannot use NTSC rf on my tv, but A|V can cope with the NTSC signal.

The TV definately registers some sort of signal.

 

I think I will start with the ram as that looks like the cause of a lot of dead XL's

[Urchlay]

If the trouble turns out to be the RAM, it's probably worth mentioning that you can replace the 64Kx1 (4164) RAM chips in an 800XL with 256Kx1 (41256) chips, which might be easier to find these days. The 256K chips will function as 64K chips in an unmodified 800XL. They're also the first step towards a 256K RAM upgrade, of course. It's OK to run a mix of 4164 and 41256 chips in an unmodded 800XL, too. If you end up having to order RAM, you may as well get a full set of 8 256K ones: they'll be about the same price, and they'll work, and if you decide to upgrade to 256K sometime in the future, the job will already be half-done.

[mimo]

If the trouble turns out to be the RAM, it's probably worth mentioning that you can replace the 64Kx1 (4164) RAM chips in an 800XL with 256Kx1 (41256) chips, which might be easier to find these days. The 256K chips will function as 64K chips in an unmodified 800XL. They're also the first step towards a 256K RAM upgrade, of course. It's OK to run a mix of 4164 and 41256 chips in an unmodded 800XL, too. If you end up having to order RAM, you may as well get a full set of 8 256K ones: they'll be about the same price, and they'll work, and if you decide to upgrade to 256K sometime in the future, the job will already be half-done.

thanks, I replaced the ram on another 800xl with the 41256 chips, not knowing that they were 256K

can you point me in the direction of the rest of the mod?

projects are stacking up at an alarming rate!

[Urchlay]

thanks, I replaced the ram on another 800xl with the 41256 chips, not knowing that they were 256K

can you point me in the direction of the rest of the mod?

 

http://www.atariarchives.org/cfn/12/02/0084.php

 

That looks like exactly what's in my dead 256K 800XL that I'm trying to fix, but the directions are hard to follow (no pictures or even ASCII line art). I didn't do the upgrade to this 800XL, it was that way when I bought it, in like 1988 or 89.

[mimo]

thanks, I replaced the ram on another 800xl with the 41256 chips, not knowing that they were 256K

can you point me in the direction of the rest of the mod?

 

http://www.atariarchives.org/cfn/12/02/0084.php

 

That looks like exactly what's in my dead 256K 800XL that I'm trying to fix, but the directions are hard to follow (no pictures or even ASCII line art). I didn't do the upgrade to this 800XL, it was that way when I bought it, in like 1988 or 89.

That looks impossible to me without any pictures or schematics!

[mimo]

The Atari gods must be smiling on me today.

The broken XL is socketed! and there is only one bad RAM chip

 

just wish my 1200 was this easy to fix

[puppetmark]

thanks, I replaced the ram on another 800xl with the 41256 chips, not knowing that they were 256K

can you point me in the direction of the rest of the mod?

 

http://www.atariarchives.org/cfn/12/02/0084.php

 

That looks like exactly what's in my dead 256K 800XL that I'm trying to fix, but the directions are hard to follow (no pictures or even ASCII line art). I didn't do the upgrade to this 800XL, it was that way when I bought it, in like 1988 or 89.

 

You can get a board from Best Electronics that makes this a million times easier! The bare board and a header is $13.50. this is the way to go.

 

http://www.best-electronics-ca.com/wizztronics_256.htm

[+Guitarman]

Also, Steve at Atarimax has a new 256/512K upgrade that isn't on the website yet. Ask him about it.