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Found these inside a non-working 71B
03-11-2018, 02:39 AM (This post was last modified: 03-11-2018 03:00 AM by Paul Berger (Canada).)
Post: #13
RE: Found these inside a non-working 71B
Pin 8 is Din and pin 9 is Dout you only need to look at the schematic to verify this. I received a non-working 71B that had two 32K modules inside much like yours. The way it was wired up they broke into chain 0 which is the chain that normally includes the four internal 4K RAM modules and the HPIL adapter. The chain starts off with the the Din pin of U6 (bottom module on right looking from the front) Dout from it goes to Din of U7 (Top right) Dout from U7 goes to U8 (Top Middle) Dout from U8 goes to Din of U9 (Left) and Dout of U9 goes to Din on the HPIL connector. The bottom middle is the OS ROM module and it does not matter because it is a hard configured module.

On the one I have have in front of me, they broke into the chain by disconnecting Dout on U7 (Top Right) from the board. Dout from U7 was routed to Din of the first 32K module Dout of 32K-1 went to Din of 32K-2, Dout from 32K-2 was then connected to the board connection where Dout from U7 used to be connected. Now the Chain is U6, U7. 32K-1, 32K-2, U8, U9, and HPIL.

The 71B I received with the extra RAM was really dead so I transferred the two 32K modules into another 71B. I also went a little further. You will note that there are pads behind the connector for U9 that looks like you could put another module on top, and you can, however to make it work you need to cut a trace on the under side of the board that connects Dout of U9 to the HPIL connector. The Dout of U9 is connected to Din of the pads for the top left as well and Dout of the top left is also by default connected Din of the HPIL connector, so cutting this one trace will disconnect Dout from U9 from Din on the HPIL. I know that this works because I have a third 32K module in this position. If you would like to do this let me know and I will take a picture of where the cut needs to be made.

Looking at the picture I see someone has added a module on the top left already.

On all of the modules pins 1-7 and 13 are all connected in parallel. The way it was wired on mine was they picked up those connections from the pads on top of one of the base RAM modules it is easier to keep track of what goes where than picking them up from vias on the board. The wire used looks like wirewrap wire which is great for things like that but does not like to be bent to often, so that is likely why you are having connection breaking.

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RE: Found these inside a non-working 71B - Paul Berger (Canada) - 03-11-2018 02:39 AM
What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM

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