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600XL keyboard issue

600Xl keyboard

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#1 Keneg OFFLINE  

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Posted Sat May 12, 2018 10:10 AM

I bought a 600 XL cheap from an eBay seller. Once I found a TV that would let me set it to channel 3, the good news is that it works. Sort of. I can get the Ready prompt, but nothing I type in shows up. If I hold down OPTION while turning it on I can run the memory check and it passes. That is certainly good news. The buttons to the right of the main keyboard seem to work, but nothing else. How do I go about troubleshooting this issue?

#2 Nezgar OFFLINE  

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Posted Sat May 12, 2018 11:16 AM

Step # 1 is to open 'er up, and re-seat the card-edge connector where the keyboard mylar is connected to the main board. Often it has corroded or come loose. While you have it separated, use a white pencil eraser to clean off oxidation off of the mylar connector contacts too before re-inserting. If you're lucky, that might be it.


Edited by Nezgar, Sat May 12, 2018 11:16 AM.


#3 Keneg OFFLINE  

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Posted Sat May 12, 2018 4:30 PM

Ok, I tried that. There was definitely oxidation there. It still isn’t working though. How would I clean the socket it plugs into? Also, if that doesn’t fix it, what’s next? All of the keys to the right of the keyboard seem to work, except help. I was able to get into the self check menu and use SELECT to scroll then START to start the tests. I’m hoping that is a cle to the problem.

#4 xrbrevin OFFLINE  

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Posted Sat May 12, 2018 4:49 PM

in my 600xl the card edge connector positioning had stressed the black mainboard socket to the point where some of the pins had snapped. i only found this out when i desoldered it as in certain positions it still worked. despite repeated attempts i could not find a permanent sweet spot so i got the iron out..

to cure it i ditched the card with the resistors on altogether and soldered in a dupont pin header to the mainboard side and a ribbon cable from the keyboard. now its 100% reliable!


Edited by xrbrevin, Sat May 12, 2018 4:51 PM.


#5 Keneg OFFLINE  

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Posted Sat May 12, 2018 5:31 PM

Ok, that sounds like a bit more than I want to do right now, but I will look at thing very carefully the next time I take it apart. Does the fact that the OPTION, START, SELECT, and RESET keys do work help to eliminate anything?

#6 xrbrevin OFFLINE  

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Posted Sat May 12, 2018 6:10 PM

those keys are controlled by another chip (GTIA i think) whereas the rest are controlled by pokey.

as a quick test, remove the intermediate resistor board and plug the ribbon directly into the black slot on the motherboard - it might work for you like it has for others. it didnt work for me due to the severed pins under the motherboard slot but its easy enough to try and doesnt make any permanent changes.


Edited by xrbrevin, Sat May 12, 2018 6:10 PM.


#7 Almost Rice OFFLINE  

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Posted Sat May 12, 2018 6:39 PM

on the edge, you can cut  a millimeter or two off the edge.  It will get you a part is less oxidized.


Edited by Almost Rice, Sat May 12, 2018 6:40 PM.


#8 Keneg OFFLINE  

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Posted Sat May 12, 2018 10:54 PM

those keys are controlled by another chip (GTIA i think) whereas the rest are controlled by pokey.
as a quick test, remove the intermediate resistor board and plug the ribbon directly into the black slot on the motherboard - it might work for you like it has for others. it didnt work for me due to the severed pins under the motherboard slot but its easy enough to try and doesnt make any permanent changes.


That is what I thought I read somewhere. I was thinking that I need to look at Pokey. Maybe remove and replace a few times to make sure it is making good contact. Does that sound reasonable?

#9 xrbrevin OFFLINE  

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Posted Sun May 13, 2018 12:12 AM

chip sockets can get 'clagged-up' with time - a re-seat is a worthwhile diagnosis :)



#10 tjlazer OFFLINE  

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Posted Sun May 13, 2018 6:20 PM

Best Electronics sells new production mylars that work better than the originals.  Highly recommend it.
 
http://www.best-elec...board Mylar.htm



#11 Keneg OFFLINE  

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Posted Mon May 14, 2018 3:48 PM

Ok, I just looked at the Best site. I guess I would need the US QUERTY Mylar? I reseated all of the larger chips. It looks like all chips on mine are socketed. Still doesnt work. A couple of times when doing the keyboard test I have gotten random characters even without touching the keyboard. The sound, which I believe is a function of Pokey, does work. Is there a way to carefully short pins on the keyboard connector to simulate key presses? This would let me know if it is a keyboard or computer issue.

#12 tjlazer OFFLINE  

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Posted Mon May 14, 2018 5:38 PM

You could have broken tracts on the Mylar. Not easy to repair, just order the new one.

#13 Keneg OFFLINE  

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Posted Mon May 14, 2018 6:12 PM

The new one costs more than I paid for the computer. Wouldn’t mind the price if I could be sure that is the problem. That is why I asked about shorting between pins on the keyboard connector.

You could have broken tracts on the Mylar. Not easy to repair, just order the new one.



#14 JR> OFFLINE  

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Posted Mon May 14, 2018 7:38 PM

try this for the matrix pinout....

 

http://mixinc.net/at...nouts/keyxl.htm



#15 Keneg OFFLINE  

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Posted Mon May 14, 2018 9:19 PM

Thanks, that should let me determine whether it is the keyboard or something in the computer.

#16 shoestring OFFLINE  

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Posted Tue May 15, 2018 3:50 PM

Haven't really read through this thread entirely.

But I think it's worth mentioning to check the two 4051 multiplexers.

#17 Keneg OFFLINE  

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Posted Tue May 15, 2018 7:01 PM

Haven't really read through this thread entirely.
But I think it's worth mentioning to check the two 4051 multiplexers.


I take it those interface between the keyboard and Pokey? It might be a while before I can really dig into this. It came with the video cable but not the TV switch box. I have an adapter coming from eBay. For testing I have been touching the center pin of the cable to the center wire of a coaxial cable. That Walter me test things, but doesn’t leave my hands free for troubleshooting. I tend to think the problem isn’t the keyboard because the keys that aren’t controlled by Pokey; SELECT, OPTION, START, RESET. work fine. They use the same mylar and connection as the rest of the keys.

So how do I test the 4051 multiplexers?

#18 shoestring OFFLINE  

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Posted Tue May 15, 2018 7:29 PM

I use a device programmer to test logic devices. ( eeTools TopMax )

But in your case I would just replace them, they're cheap. A couple of bucks for both. Just drop the new ones in.

Should be able to buy them from any electronics hobbiest store.

Edited by shoestring, Tue May 15, 2018 7:30 PM.


#19 Keneg OFFLINE  

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Posted Wed May 16, 2018 4:37 AM

I have some ordered.

#20 shoestring OFFLINE  

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Posted Wed May 16, 2018 4:49 AM

Have you checked the Mylar ?

 

Those keyboards aren't too difficult to assemble and disassemble. 



#21 Keneg OFFLINE  

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Posted Fri May 18, 2018 3:05 PM

Have you checked the Mylar ?
 
Those keyboards aren't too difficult to assemble and disassemble.


Because the keys that are not controlled by Pokey work, I am inclined to rule that out. I should get the 4051 chips soon. If that doesn’t fix it, I will unplug the keyboard and use a short piece of wire to simulate key presses. That should let me determine if the computer circuitry is OK. I will only look at the keyboard once I am sure the rest is OK.

#22 shoestring OFFLINE  

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Posted Fri May 18, 2018 10:05 PM

I take it those interface between the keyboard and Pokey? 

 

POKEY ( inputs K0-K5 ) reads the keyboard via the 2 4051 muxes.

 

If none of the other keys work then there's a good chance that there's a problem with the POKEY. But also just as likely that both muxes are dead.

 

Since you've already tried reseating,  maybe give the pins and sockets a good clean as a last resort before replacing the muxes and the POKEY ( in that order ).


Edited by shoestring, Fri May 18, 2018 10:05 PM.


#23 Keneg OFFLINE  

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Posted Sat May 19, 2018 8:14 PM

POKEY ( inputs K0-K5 ) reads the keyboard via the 2 4051 muxes.
 
If none of the other keys work then there's a good chance that there's a problem with the POKEY. But also just as likely that both muxes are dead.
 
Since you've already tried reseating,  maybe give the pins and sockets a good clean as a last resort before replacing the muxes and the POKEY ( in that order ).


I got in the 4051s today. Changed them and now it won’t even boot to basic. Put the old chips back in. Still no go just a screen black on top and mostly white on bottom. It may be beyond what I can diagnose and fix now. Sigh.

#24 Keneg OFFLINE  

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Posted Sat May 26, 2018 2:34 PM

It turns out that is was the keyboard mylar. Near the power light there are two contacts. They were black. Cleaned them and reassembled the keyboard. It works! If only I hadnt lost one of the springs. So the help key doesnt work. All other keys work fine. So does anyone know where I can get one of these springs? I need the steel one that is used for the right side keys. The rest of the keys use copper or brass springs.

One note. On both the 600 and 800XL, entering the keyboard test from All Tests does not work right. I have to select it separately. Then all keys, except Help work fine.

Edited by Keneg, Sat May 26, 2018 2:42 PM.


#25 Wrathchild OFFLINE  

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Posted Sat May 26, 2018 4:54 PM

in my 600xl the card edge connector positioning had stressed the black mainboard socket to the point where some of the pins had snapped. 

 

In fitting an internal MyIDE I've just experienced something similar as it looks like the keyboard connection to the motherboard was only held in by four or five of the pins being soldered, so having it bend back and forth a number of times has seen it fall off  :_(







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