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To socket or not to socket - TMS9900


8 replies to this topic

#1 Pepper OFFLINE  

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Posted Sun Nov 12, 2017 8:51 AM

I know reliability comes to mind. But what are the pros and cons of when replacing the TMS9900 that you bung in a DIP socket to make life easier the next time ?

Inquiring minds want to know :) 

 

 



#2 Ksarul OFFLINE  

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Posted Sun Nov 12, 2017 9:46 AM

I tend to socket any chips I remove as a general rule, as it limits potential damage to board traces over the long term. I just use gold plated machine-pin sockets when I can find them. They are a bit harder to find for the 64-pin 9900 chip, but I just looked in my parts box and turned up about 20 of them, so they are out there.



#3 Lee Stewart OFFLINE  

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Posted Sun Nov 12, 2017 9:48 AM

Though the TMS9900 does not have as sturdy a pin construction as modern CPUs that routinely use them, perhaps  (if there is room) a ZIF socket would be the best choice.

 

...lee



#4 matthew180 OFFLINE  

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Posted Sun Nov 12, 2017 2:10 PM

I would not use a ZIP socket.  I don't think they are designed for long-term mounting of chips, and they are expensive.  Also, I can't remember ever having to replace the 9900 CPU itself, so a ZIF socket for such a rare event would be overkill, IMO.

 

If a 64-pin socket cannot be found, you can always use SIP pin headers.



#5 Pepper OFFLINE  

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Posted Sun Nov 12, 2017 6:49 PM

I would not use a ZIP socket.  I don't think they are designed for long-term mounting of chips, and they are expensive.  Also, I can't remember ever having to replace the 9900 CPU itself, so a ZIF socket for such a rare event would be overkill, IMO.

 

If a 64-pin socket cannot be found, you can always use SIP pin headers.

SIP pin headers will work nicely, they are very handy !

Finding a 64 pin DIP that is 2.54mm pitch seems to be hard on eBay, but Mouser has them.

I need to go through troubleshooting this spare board that I have again, before I start unsoldering everything. The -RESET line is set high all the time... which makes me suspect the TMS9900.



#6 Ksarul OFFLINE  

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Posted Sun Nov 12, 2017 9:25 PM

Here is one good one, and I buy stuff from this vendor all the time. Here's another one that ends up a little cheaper because it only gives you two (instead of six).



#7 Stuart OFFLINE  

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Posted Mon Nov 13, 2017 3:24 AM

 

I need to go through troubleshooting this spare board that I have again, before I start unsoldering everything. The -RESET line is set high all the time... which makes me suspect the TMS9900.

 

Have you tried replacing the TIM9904 clock chip which generates /RESET? (May be a 74LS362 on very early boards.) It is sometimes already socketed which makes life easy.


Edited by Stuart, Mon Nov 13, 2017 3:34 AM.


#8 Pepper OFFLINE  

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Posted Mon Nov 13, 2017 7:24 PM

 

Have you tried replacing the TIM9904 clock chip which generates /RESET? (May be a 74LS362 on very early boards.) It is sometimes already socketed which makes life easy.

No I've not tried replacing it yet. It's not socketed on this board.. (My working TI99/4A is lol). I'm going to do more poking around before unsoldering the beast... 



#9 helocast OFFLINE  

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Posted Mon Nov 13, 2017 9:31 PM

Here is one good one, and I buy stuff from this vendor all the time. Here's another one that ends up a little cheaper because it only gives you two (instead of six).

Used both as I keep them in my watch list! Sometimes we're on the same wavelength. :)






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