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Found these inside a non-working 71B
03-11-2018, 01:45 PM (This post was last modified: 03-11-2018 02:01 PM by MikeSD.)
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RE: Found these inside a non-working 71B
(03-11-2018 02:39 AM)Paul Berger (Canada) Wrote:  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.


Thanks Paul, this is exactly how mine is wired, except after my 32k RAMs, the Dout runs over to a FORTH module before continuing to HPIL. I'm still assuminv it's a FORTH module, for now. Can't make out the last digit of p/n. The thing that was confusing me was that would bave meant a cut wire on the board, which now mames since with your reply.

I think I have a good understanding on how this all goes now. I numbered the pins in my photo just above. Guess I have it right since 8 an 9 are correct using that convention.

I'm going to strip it all out and put new wires and reflow solded on the left chips, if my 72 year old eyes can still see that well Wink I think I can. One has movement (the chip, not my eye). Want to get the 71B working before reinstalling everything. If it doesn't work, I have another candidate.


1) I have a couple versions of the museum DVDs if I can find them but I don't recall a schematic. What doc was that in?

2) Looking at my photo above there are 6 mem chips. Is this how they are numbered?
left (Bottom) U6, left (Top) U7, middle (Top) U8, middle (B) U?, right (T) U9, right (B)U?. The right chip in my photo is different from left, I assumed it was the ROM.

3) Any idea what the buzzer mod is for?

Thanks again for the help.
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RE: Found these inside a non-working 71B - MikeSD - 03-11-2018 01:45 PM
What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM

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