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Jonny swanny

Help me! I’m stuck! Atari 400 repair

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Ok guys, I’m stuck. I’m only 16 so I don’t reeeeeeeally know what I’m doing, but I need your help! Atariage, I’ve been scammed!! DUN DUN DUUUUUUUUN!! I bought a “working” atari 400 off of OfferUp whose only problem was that it had a cut video cable (Which I replaced with one I pulled from a broken 2600) and no PSU (which I had bought before the system arrived). I, being the idiot I am, DIDN’T test the system before starting my cleaning/retrobrite process (pictures below ;) ). After that week of school I threw the system back together aaaaaaaand... black screen... :(

 

I’ve tried Everything I can think of, I reseated all the chips on the whole computer (cleaning the pins and the sockets as I did), cleaned the the ram and cpu board connectors, started it up with a star raiders cartridge, made sure everything was grounded properly, deoxidized the power jack, cleaned the channel selector, tried multiple tv’s (both new and old), and STILL I get that black screen... 

 

WHAT SHOULD I DO?!

 

Any help would be greatly appreciated!

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Can you show us a picture of the 'black screen'? Does it 'pop' or make other noises when you turn it on? Are you sure that your channel switch matches your TV? Does the power LED come on? Can you check the voltages with a meter?

 

What you may need is a second, known good 400 for parts swapping...

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Can’t get a picture of the screen just yet, but it’s solid black (not a no signal). No funny noises. Quite sure about the channel. The LED comes on, yes. And no, I haven’t got a voltage meter :/

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15 minutes ago, bob1200xl said:

What you may need is a second, known good 400 for parts swapping...

And I would, but you see, there’s an issue... money.

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Sorry for the bombardment of comments, but here’s the whole situation. 
1. the screen is now green sometimes and black other times

2. The built in speaker makes an almost imperceptible tick noise when starting up

3. channel is correct, yes

4. LED is on

5. In fixing the power jack (it would only work if I put pressure on the cable), the door detector switch broke in half (I just jumped it with a piece of speaker wire)

6. Picture of screen below (The green on the screen is darker (almost navy) in person than in the photo)

7. I don’t have access to another 400

image.jpg

image.jpg

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Did you do something to get a green screen? Have you tried it without the cartridge?

 

You need to start swapping boards and such. Have you opened the shielding? Can you show me the cards and boards inside? If you unscrew anything, make sure you know how to put it back - take pictures or something.

 

 

 

Bob

 

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Totally. I’ve had it completely apart, like I said, I’ve previously reseated and cleaned all the chips, sockets, and boards with isopropyl alcohol. I’ll try I out with no/other cartridges. The boards (CPU and RAM) inside look fine, tip top shape (yes, I know that doesn’t say much, but I figured I’d mention it). If you’re curious, it’s a 16K model. I got the green screen by deoxidizing the power jack because I thought it might not be getting enough power, and I’m guessing that’s what did it. I heard on another thread that the rom chips may be the culprit, would a different cartridge bypass the ROMs, I’ve heard star raiders can boot even if the system is faulty in certain areas.

 

I’ll get on that. Thanks for your help thus far.

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How did you clean the chips with ipa? afaik it's best to use brushes designed to clean chips and not a toothbrush.

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My WAG is RAM.

 

If you can find someone near you with an 800 (or 400), maybe you can try swapping a RAM board with them?

 

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I cleaned the chips with a Q-Tip and made sure not to go against the grain of the pins, is there a special tool for cleaning chips? I haven got one, whatever it is. The power supply is correct, it’s an OEM 400 power supply confirmed to be in working order. I would try to meet up with someone, but I’m not sure how I should go about that. Perhaps I should just buy another 400, swap parts and figure out what’s wrong, and sell it. Either way, I can certainly leave the system on a while and see if the RAM starts getting hot.

 

Swapping cartridges didn’t help anything, but in doing so, I realized something. (See video)

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I’m not sure why the video didn’t work, this is what it said.

 

the power supply is 100% correct and working

 

with no cartridge inserted, I get a black screen unless I turn the system on and off around five time, at which point the screen turns green

 

with any of the following cartridges inserted (popeye, pitfall, Pac-Man, eastern front, keystone Kapers, the dreadnaught factor, Galaxian, qix, gorf, silicon warrior, astrochase, basic, and defender) I ALWAYS get a GREEN screen

 

when I insert Star Raiders (which I’ve heard doesn’t use much of the parts of the system) I ALWAYS get a BLACK screen 

 

all cartridges have been cleaned

 

NEXT: I will clean the cartridge port, reseat ram chips and board, reseat rom chips. Here’s to hoping

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Ok, so I’ve powered up the computer minus each ROM chip individually, the one pictured below was the only one that did anything. When removed a green screen appeared every time. At this point, I think I just need to buy another 400 and part swap...

image.jpg

image.jpg

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Well, that one IC is half of the OS ROM. The other two chips are the other half of the ROM and the 2K Floating Point ROM. They have been known to go bad, though I don't know how common that is. You can buy replacement ICs from Best Electronics, though there is a minimum dollar amount for orders, and the owner has some idiosyncrasies that put off some folks. You might be able to find someone with a donor machine who can provide you a replacement chip for less than the cost of an entire 400.

 

But of course, that chip might not be bad at all - the suggestion above about a possible bad RAM chip is also a good one; spare 400 16K RAM boards are also available from BEST. I don't recall off-hand if the 800's 16K boards are interchangeable with the 400 - @bob1200xl or @ClausB probably know. If so, spare 16K 800 boards are pretty easy to find too.

 

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Yeah, I think the easiest thing for me to do is just buy another working 400. Pinpoint the fault in mine, fix it, and sell off the one I don’t want. Hopefully then I’ll not have lost a ton of cash in the whole exchange.

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1 hour ago, DrVenkman said:

But of course, that chip might not be bad at all - the suggestion above about a possible bad RAM chip is also a good one; spare 400 16K RAM boards are also available from BEST. I don't recall off-hand if the 800's 16K boards are interchangeable with the 400 - @bob1200xl or @ClausB probably know. If so, spare 16K 800 boards are pretty easy to find too.

 

 

They are interchangable (assuming you remove the plastic casing on the 800's RAM cards).  I have a bunch of spares.   If @Jonny swanny wants to PM an address I'll send you one next week.

 

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Let me just comment that you do a beautiful job of cleaning that thing up.  I know it doesn't work, but for just starting out and not knowing much about these, its nice to see the thing clean!

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do you have another 16k memory module to swap in?

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2 minutes ago, xrbrevin said:

do you have another 16k memory module to swap in?

Unfortunately no, I can buy one if worse comes to worse.

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1 hour ago, kheller2 said:

Let me just comment that you do a beautiful job of cleaning that thing up.  I know it doesn't work, but for just starting out and not knowing much about these, its nice to see the thing clean!

Haha, Thanks! Love seeing these old computers like new. (Hopefully I can get them to work like new as well :) )

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I don't know if this will help you, but I have a 400 that turns on with a green screen. However, it works every time if I squeeze the top and bottom of the case near the power switch when turning it on. I've reseated chips, used contact cleaner on the connectors and reflowed much of the solder in that area and nothing has fixed it yet. At least I feel like I'm narrowing in on the problem.

Good luck with this project. You did an amazing job cleaning it up.

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4 hours ago, Jonny swanny said:

Hmm. I’ll definitely have to give that a try. Thanks for reaching out! :D 

Here's a link to my Atari 400, very similar issue, troubleshooting adventure.  My debug steps turned up a bad OS ROM chip, A105, the bad chip, of which, was only verified/validated after swapping like 10 times between two Atari 400 systems.  Good luck with your system. 

~ Trellot

 

 

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