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Decoupling Capacitors for memory chips on motherboard

memory circuit 1200XL MB motherboard

2 replies to this topic

#1 rockdoc2010 OFFLINE  


    Chopper Commander

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Posted Sat Feb 1, 2014 5:40 AM

Hello there,


I am building a 1200Xl from scratch. On the motherboard there are what appear to be decoupling capacitors that are located between pin 8 and pin 16 on the memory chip. C16 - C23


I am wanting to install gold plated machine pin sockets that come with a decoupling capacitor installed in the frame of the socket.


The Atari schematic calls out 0.1uF on the motherboard.

The Capactor in the frame is also 0.1uF


That would give 0.2uF per memory chip if I installed the caps in the board.


Do I just replace the caps on the MB with wire, omit them entirely or leave the caps in the motherboard?


Thank You


Douglassocketsmall.jpg Attached File  memdetail.bmp   2.61MB   112 downloads

#2 5-11under ONLINE  


    River Patroller

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Posted Sat Feb 1, 2014 8:15 AM

Don't add a wire. That will make a short between V+ and GND.

Two choices: Don't install the capacitors on the MB (0.1 uF result), or install the capacitors on the MB (0.2 uF result). Either is fine. I'd probably do the 2nd.


Edit: also verify that the last pin on either side of the DIP package is okay to have that capacitor. There may be cases where those two pins are not voltage inputs.

Edited by 5-11under, Sat Feb 1, 2014 8:16 AM.

#3 1050 OFFLINE  



  • 1,116 posts

Posted Thu Feb 13, 2014 12:43 PM

Use both caps, if you'll go to the Atmel website and do some looking thru their application notes you'll find one where they universally recommend upping the standard .1 uf ceramic to .22 uf ceramic across the board for decoupling caps.  So it's really a non-issue?  Do what you want.

Also tagged with one or more of these keywords: memory, circuit, 1200XL, MB, motherboard

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