Atari 1200XL

[+DrVenkman]

Did you actually clean the contacts on the mylar? I've disassembled and repaired two 1200XL keyboards and in each case, in addition to repairing the traces at the mylar edge connector, I also cleaned the key contacts on both sides with isopropyl alcohol. Never experienced a problem like that. I'm going to do a third 1200XL mylar at some point this weekend or next as well.

[erichenneke]

Did you actually clean the contacts on the mylar? I've disassembled and repaired two 1200XL keyboards and in each case, in addition to repairing the traces at the mylar edge connector, I also cleaned the key contacts on both sides with isopropyl alcohol. Never experienced a problem like that. I'm going to do a third 1200XL mylar at some point this weekend or next as well.

Are you saying to peel up the top layer of mylar and clean the contacts on the inner sides of the two sheets?

 

I didn't want to risk screwing it up by peeling it apart unless that really will address the issue. It just seems weird to me that the entire thing works when i even slightly touch every single key "pad" with the mechanical keyboard-assembly detached.

 

Of course, it is no good to me as-is either since only a few keys continue to work when i put it back together! So I am will to give it a try.

 

Can you confirm that's what you mean though? Peel it aparts and clean contact points on both sides with alcohol before putting it back together?

 

thanks!

-Eric

[erichenneke]

That exact same problem drove me crazy, and I never found a solution.

 

Touch the pad when apart, works every time. Put together, doesn't work at all.

 

New mylar from Best is my recommendation.

Ok, well at least this is not a unique case then! has been driving me crazy too.

 

So did using a Best mylar address that situation you ran into?

 

-Eric

[+DrVenkman]

Are you saying to peel up the top layer of mylar and clean the contacts on the inner sides of the two sheets?

 

I didn't want to risk screwing it up by peeling it apart unless that really will address the issue. It just seems weird to me that the entire thing works when i even slightly touch every single key "pad" with the mechanical keyboard-assembly detached.

 

Of course, it is no good to me as-is either since only a few keys continue to work when i put it back together! So I am will to give it a try.

 

Can you confirm that's what you mean though? Peel it aparts and clean contact points on both sides with alcohol before putting it back together?

 

thanks!

-Eric

 

Yes. In addition to the contact edge connector fix here ...

 

http://retrobits.net/atari/keyboard.shtml

 

... I also use a hair dryer to heat up the white silicone and very gently (and patiently!) remove the silicone and clean the contacts. It makes for a rather tedious job but it's worked well on the two I've done.

[erichenneke]

 

Yes. In addition to the contact edge connector fix here ...

 

http://retrobits.net/atari/keyboard.shtml

 

... I also use a hair dryer to heat up the white silicone and very gently (and patiently!) remove the silicone and clean the contacts. It makes for a rather tedious job but it's worked well on the two I've done.

 

I decided to go for it and... IT WORKED !!!

 

Sweet! Thanks!

 

Next I'll try those modifications Bob1200XL suggested for the video beacuse, well, the video isn't so great on this 1200XL compared to a 130xe or even a standard 800xl.

 

-Eric

[+DrVenkman]

 

I decided to go for it and... IT WORKED !!!

 

Sweet! Thanks!

 

Next I'll try those modifications Bob1200XL suggested for the video beacuse, well, the video isn't so great on this 1200XL compared to a 130xe or even a standard 800xl.

 

-Eric

 

Glad it worked for you - congratulations! It's a pain in the ass but I'd rather spend time than money these days. I actually find it soothing to do work like this.

 

As for Bob's video fix, it's great and works very well. If you're willing to spend $25 (and wait until Bryan has the next batch of UAV video boards in from his supplier), the results are fantastic. I have two of them in 1200XL's, a third in an 800XL and a fourth in a 2600 4-switch machine. In a 1200XL it's dead-simple to install: remove the 4050 from the video circuit, insert the assembled UAV, solder one wire for color input to the UAV, and then three output wires: composite, chroma and luma. You can also do separate ground and power lines if your particular machine has "noisy" power in the 4050 socket, but it's not necessary in all machines.

[Brentarian]

Dr.Venkman is right about the UAV boards. I just put one in a 400 and the video quality is amazing.

[erichenneke]

I would advise anyone who needs to fix their 1200XL keyboard to get a new mylar from Best. You can attempt to fix the old mylar, but it is not always successful. Best's mylar is pretty bullet-proof.

 

Best has an interposer thing for their k/b, but I never use it. If the mylar isn't making good contact (on Best's mylar), just open it up and re-position/clean the contacts.

 

The other thing to fix on any 1200XL is the video. Simple fix is to replace C115 and L15 with a wire or 1 ohm resistor.

 

Last, replace R63 with a wire (or 1 ohm resistor - looks better) to power the SIO.

 

You're good to go!

 

Bob

Hi Bob,

I just made these 3 changes to C115, L15 and R63. I just replaced all three with wires directly.

 

Before I made the change there was some erratic flashing, almost like occasional interference for lack of better way to describe it. After these 3 changes the signal is consistent and doesn't flash any longer. So that's the good news.

 

However, I think the picture was actually a bit sharper before the change, and the colors look washed out now... for example if i go to Atari basic i can barely make out the difference between the default background color and the text color. It wasn't great before I made these changes either, but now it seems even a little worse.

 

Any suggestions?

 

Thanks!

-Eric

Edited October 15, 2017 by erichenneke

[+DrVenkman]

However, I think the picture was actually a bit sharper before the change, and the colors look washed out now... for example if i go to Atari basic i can barely make out the difference between the default background color and the text color. It wasn't great before I made these changes either, but now it seems even a little worse.

 

 

Can you provide pictures of your current results? It sounds like it might be a bad 4050 chip.

[erichenneke]

 

Can you provide pictures of your current results? It sounds like it might be a bad 4050 chip.

here you go. taking a picture of a CRT is always fun.

I can mess with the little color adjustment inside the 1200XL and get the basic blue/text screen to look much better but then the colors are all wrong for everything else I do on the system.

This is all using the composite output by the way.

 

Also, the flicker is actually still there too. It seems it only happens when the SIO cable is plugged in. Last night I had it unplugged so it wasn't flickering. So unfortunately that isn't fixed yet either, but at least i know it seems to be related to SIO.

[+DrVenkman]

Yeah, that is really, really bad. You've got something fubar in the video circuit.

[+bob1200xl]

What does it look like on the LUMA output?

 

What does the SIO plug into? Is there a series of devices?

 

Yes, it looks terrible.

 

Bob

[erichenneke]

Yeah, that is really, really bad. You've got something fubar in the video circuit.

i found a pretty good "happy medium" for now that looks decent for text on blue default screen and the colors seems right for most games. It's not as crisp as i'd like it to be but for now it is fine.

 

Do you have any suggestions?

[+DrVenkman]

The easiest thing to try is to replace the 4050 chip. They are less than 50 cents each from any online electronics supply store. You might also have a bad GTIA, which is pretty cheap from Best Electronics but they have a minimum order. I'd have to dig through the video schematics to come up with other suggestions.

[erichenneke]

thanks for your suggestions and help.

 

I'm still just happy to see every key on the keyboard working again!

[erichenneke]

The easiest thing to try is to replace the 4050 chip. They are less than 50 cents each from any online electronics supply store. You might also have a bad GTIA, which is pretty cheap from Best Electronics but they have a minimum order. I'd have to dig through the video schematics to come up with other suggestions.

I replaced the 4050 with one from a non-functioning 800xl board. It pretty much seemed the same either way.

 

Then I swapped the GTIA from the non-functioning 800xl board. That seemed to improve it a bit, but not a dramatic difference.

 

Since this is the only 1200XL I have ever owned I am not quite sure what "good" should look like. How should it compare to the composite output from a standard NTSC 800XL ?

[gilsaluki]

Yeah. Brad does great work with our OLD A$$ good stuff. Get the new mylar.

[+DrVenkman]

Since this is the only 1200XL I have ever owned I am not quite sure what "good" should look like. How should it compare to the composite output from a standard NTSC 800XL ?

Should be about the same, perhaps a bit over saturated by comparison. Here’s what an unmodded 1200XL rainbow logo should look like in Composite:

 

[erichenneke]

Should be about the same, perhaps a bit over saturated by comparison. Here’s what an unmodded 1200XL rainbow logo should look like in Composite:

 

Yes, the rainbow logo looks fine.

 

"a bit over saturated" is a good description so maybe this is just what it is supposed to look like.

 

For example, on a game like Quasimodo the bricks look very pink and brighter than the other colors ( "over saturated" is exactly the words that came to mind when I saw this).

 

I am still getting occasional intermittent stutter, like a noisy signal or interference. I thought it was related to something being plugged into the SIO but I see now it happens sometimes without anything in the SIO port as well. It definitely seems more frequent/pronounced with a disk drive attached to SIO though.

 

Question, what are those changes to C115, L15 and R63 intended to address/improve?

 

Thanks!

-Eric

[+DrVenkman]

R63 merely adds +5VDC to the SIO port, if I remember correctly. The other changes help remove some blurriness in the video signal.

 

Edit: I dig around and found some quick pics I took over the summer when I was restoring one of my 1200XL’s, before I put a UAV board into it. This is stock 1200XL video: