Model 200 RAM: Difference between revisions

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The model 200 comes with 24k built in, and supports up to 2 more banks of 24k in the form of ceramic dip modules that plug into the Option RAM #1 & #2 sockets.


*[https://oshpark.com/shared_projects/tepuH2VQ PCB by Steven Adolf]
=TANDY 26-3866=
The original 24K module was Catalog Number 26-3866.<br>
This is a ceramic DIP carrier with 3 8k sram chips and a 40H138 to decode A13 & A14 into 3 different /CS for the individual SRAM chips.
 
[[File:TANDY_26-3866_top.jpg|200px|link={{filepath:TANDY_26-3866_top.jpg}}]]
[[File:TANDY_26-3866_bottom.jpg|200px|link={{filepath:TANDY_26-3866_bottom.jpg}}]]
 
[[File:TANDY_26-3866.svg|frameless|link={{filepath:TANDY_26-3866.svg}}]]
 
=Modern Replacements=
 
https://github.com/bkw777/TANDY_200_RAM
<gallery>
File:TANDY_200_RAM.jpg
File:TANDY_200_Dual_RAM.jpg
File:TANDY_200_Dual_RAM_tsop_14mm.jpg
</gallery>
 
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This module, designed by Steven Adolph, adds both possible optional 24K banks, for a total of 3 banks when installed.
 
UPDATE: The pcb and parts below have been replaced by this updated design:
*[https://oshpark.com/shared_projects/o1iXGzr1 PCB]
*[http://www.digikey.com/short/jmq927 Parts]
 
This is parts to build a single board, although OSHPark will ship you 3 boards. You only need one board for one Model 200 computer. If you want to build all 3 boards, then triple all the part quantities on the digikey cart.
 
OLD VERSION:
*[https://oshpark.com/shared_projects/tepuH2VQ PCB]
*[http://www.digikey.com/short/q71vcp Parts]
*[http://www.digikey.com/short/q71vcp Parts]
::(1) TC551001 128kB SRAM
::(1) TC551001 128kB SRAM TSOP32 package
::(1) 74AHC1G08 AND gate
::(1) 74AHC1G08 5-pin AND gate
::(1) 0805 1uF ceramic cap
::(1) 1uF ceramic capacitor, 0805 package
::(29) round pins
::(29) round pins


The ram in the DigiKey cart above is not yet tested and verified to be a working drop-in replacement for the original specified ram.
This is enough parts to build 3 boards, because you can't order less than 3 PCBs from OSHPark anyway. But you only need 1 board total per Model 200. The single new board takes the place of both ram sockets. You can reduce the part quantities in the DigiKey cart before ordering.
 
The pins are installed by pulling the pins out of the plastic insulator, and dropping the pins into the holes from the top, then soldering, then cutting off the top. You need 29 pins per board, so one 32-pin stick provides all the pins for one board.
 
[[File:200_ram_sa_1.jpg|200px]]
[[File:200_ram_sa_2.jpg|200px]]
[[File:200_ram_sa_3.jpg|200px]]
[[File:200_ram_sa_4.jpg|200px]]
[[File:200_ram_sa_5.jpg|200px]]
[[File:200_ram_sa_6.jpg|200px]]
[[File:200_ram_sa_7.jpg|200px]]
[[File:200_ram_sa_8.jpg|200px]]
[[File:200_ram_sa_9.jpg|200px]]
[[File:200_ram_sa_10.jpg|200px]]
[[File:200_ram_sa_11.jpg|200px]]
[[File:200_ram_sa_12.jpg|200px]]
[[File:200_ram_sa_13.jpg|200px]]
 
[https://photos.app.goo.gl/g1G4bo6FbjJSgcqU2 More Pics]
 
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=More info=
 
https://archive.org/details/Model_200_Portable_Computer_Service_Manual_19xx_Tandy/page/n75/mode/2up
 
http://bitchin100.com/wiki/index.php?title=Tandy_200_RAM


This is enough parts to build 3 boards, because you can't order less than 3 PCBs from OSHPark anyway. But you only need 1 board total per Model 200. The single new board takes the place of both ram sockets. You can reduce the parts quantities in the DigiKey order.
http://club100.org/memfiles/index.php?&direction=0&order=&directory=Steve%20Adolph/T200%20Ram%20module


There will be a few unused pins left over. The order is for 3 sticks of 32 pins each. You will break away and use 14 + 14 + 1 pins from 1 stick for each ram module.
http://club100.org/memfiles/index.php?action=downloadfile&filename=m200ram.txt&directory=Steve%20Adolph/mods_to_upgrade_ram

Latest revision as of 19:38, 18 September 2022

The model 200 comes with 24k built in, and supports up to 2 more banks of 24k in the form of ceramic dip modules that plug into the Option RAM #1 & #2 sockets.

TANDY 26-3866

The original 24K module was Catalog Number 26-3866.
This is a ceramic DIP carrier with 3 8k sram chips and a 40H138 to decode A13 & A14 into 3 different /CS for the individual SRAM chips.

Modern Replacements

https://github.com/bkw777/TANDY_200_RAM


More info

https://archive.org/details/Model_200_Portable_Computer_Service_Manual_19xx_Tandy/page/n75/mode/2up

http://bitchin100.com/wiki/index.php?title=Tandy_200_RAM

http://club100.org/memfiles/index.php?&direction=0&order=&directory=Steve%20Adolph/T200%20Ram%20module

http://club100.org/memfiles/index.php?action=downloadfile&filename=m200ram.txt&directory=Steve%20Adolph/mods_to_upgrade_ram