Found these inside a non-working 71B

[MikeSD]

(03-11-2018 08:27 PM)Paul Berger (Canada) Wrote:  [quote='rprosperi' pid='92797' dateline='1520799314']

It appears to have all the connections it needs there are 3 pins next to +5 that are of no use to a RAM or ROM module they are there because these modules are designed to be put into front side plugins The fourth missing connection is Dout which is not brought back to the board because it goes on to connect to the other added RAM and ROM modules.

Paul.

I'm not sure about that. The chip above U9 definitely has part number of MATH. Any chance a 2nd FORTH module might be under the same goop with the first? As far as I can tell those are the only installed points. So if it's not there, it never was

I also think the FORTH does go back to HPIL Din. I think it had a wire going from FORTH pin back to HPIL. You can barely see it in this pic. First page photos 5 and 6 show wire going from FORTH to HPIL. Pin9 goes behind resistor that picks up the HPIL chain.

I was looking for an easy way to break into the chain on a working 71B and I'm not sure I have to. Looks love HP might have planned for this. U9-pin goes two places. See pic. I might just be able to tack the RAM to that single alone chip, on another calc and just connect pin 9 of it and run it to RAM and don't connect an HPIL



But I'm confused now. You have been talking about a U9 chip. I have been under the impression that is the normal chip in an unmodified 71B. And the chip above it is the odd chip. Shown top left, in this pic. I thought that was a MATH chip, based on the part number. I don't see any place for a 2nd ROM for forth. The top left I'm calling a Math chip. I also suppose I might not have two 32k RAMs. It might be the missing FORTH ROM and something else. I've been assuming it's all RAM but I could be wrong. Never looked at it very closely. I was thinking I might replace those wires, so I will be able to get to the bottom of that.

But, using this pic above which are RAM and which are ROM. i thought the 4 to lect were 4K RAMs, and the 5th on bottom left was a RAM also (or a ROM). and that the only suspect is the Math, top left.

BTW, found something interesting in shaf I thought aas 64K RAM. Photo coming. Last 2 photos.