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New to 8-bit Atari computers - 800 XL Trouble


bushnrvn

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I picked up an 800 XL and a handful of games a couple weeks ago. I've been having some trouble getting video out of it. Right now the composite line on the 5 pin DIN is showing a slightly less than black screen with a faint vertically scrolling gray bar. No audio, and game carts have the same output.

Troubleshooting done so far:

Tried several monitors including a 1702 - the luminance and chroma channels are putting out garbage.

Cleaned motherboard.

Reseated all ICs

touched up a couple bad solder joints

Note: I don't have another 800 XL to test with.

 

A little bit of research has led me to the very likely possibility that the power supply is the culprit. While I keep looking for my multimeter (still unpacking from a move) I thought I'd ask for your input. Does this sound familiar to anyone?

Edited by bushnrvn
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Need more info to troubleshoot properly.

 

1. What region are you in (NTSC, PAL, SECAM)?

 

2. Did you buy or build a cable yourself?

 

3. Have you tried RF to be sure it's actually booting up properly?

 

For a start. We might have more questions depending on your answers.

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Okay, NTSC 800XL's don't have Chroma connected to the DIN jack. So you won't get Chroma/Luma video from the Atari monitor jack without performing a fairly simple mod. You'll have to use Composite. Also, it looks like the Atari and Commodore pinouts are not 100% identical but if your C64 cable is a standard 5-pin DIN, then if you use Composite it should work. Not sure why it's not off-hand.

 

For connecting to RF, all you need is a cable with a standard RCA male plug to connect to the 800XL RF Out and either an old manual switchbox (NOT an NES powered switchbox) or better, an RCA-to-F-type Coax adapter. Something like this: https://www.amazon.com/uxcell-Straight-Connector-Coaxial-Adapter/dp/B00LUS30QM/ref=pd_lpo_vtph_23_lp_tr_t_3?_encoding=UTF8&psc=1&refRID=5NZ3P8SKQHHDX8NFZ2KB

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Thanks.

 

Photo of the output is attached. This is accompanied by a constant buzz.

 

 

Yeah - more research lie telling me the "ingot" epoxy PSU is notoriously bad. Buzzing on the RF line ...fingers crossed that my unit isn't toast.

 

Ugh. Yeah. Dig up that mulitmeter and test the ingot before you use it again. Assuming it's NOT fried the machine, get a different PSU pronto!

 

In the meantime, how is that XL connected to the TV? You mentioned having NES and Genesis RF switchboxes. I don't *think* those will work but it's been a long time since I've even seen a non-Atari/non-mechanical switchbox.

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Dumb question but have you tried channel 2 and/or working the channel select switch back and forth several times? The switches can get cruddy with age - working them a few times, especially if you spray them with electrical contact cleaner, can help if that's the problem. Now having said that, I'd be really concerned about that power supply.

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1. NTSC

 

2. Its a store bought cable I use with my Commodore. It is pretty old but I know it works.

 

3. I don't have a modulator that will work with the Atari 800 XL - unless any old modulator will work? I've got some NES\Sega modulators.

Also, the monitor pinout is different from the C64 so you'll have to swap the RCA plugs around.

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New PSU arrived today. Looks like that issue is resolved.

Sadly, whether it was the original PSU or something else, the 800XL is in need of more diagnosis\repair. On power up, the screen may flash a sort of off-white or dark red, always ending on black.

Time to start testing ICs. I don't have any replacements or another 800XL on hand, so this may be it for awhile.

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So I have left this thing running for about ten minutes - none of the RAM chips are hot, but the CPU and GTIA are a little warmer than the rest of the chips. My assumption is this is normal.

I do see, however, that U26 and U27 have blackened pins. These are RAM demux chips, correct?

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So I have left this thing running for about ten minutes - none of the RAM chips are hot, but the CPU and GTIA are a little warmer than the rest of the chips. My assumption is this is normal.

 

I do see, however, that U26 and U27 have blackened pins. These are RAM demux chips, correct?

 

CPU and GTIA normally run warm.

 

U26 and U27 are the 74LS158 discrete logic chips. Are they socketed on your board (some 800XL's have these socketed, some not). "Blackened" doesn't sound good - sounds like perhaps the machine got zapped by a failing power supply. On the other hand, it could just be age-related surface corrosion. Pics would help. What would help even more would be a logic probe reading on the outputs to see if they're active. And for that matter, a logic probe would let you see if the rest of the chips are acting normally.

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  • 3 weeks later...

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