Found these inside a non-working 71B

[Paul Berger (Canada)]

(03-11-2018 09:51 PM)MikeSD Wrote:  [quote='Paul Berger (Canada)' pid='92799' dateline='1520800020']

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.

(03-11-2018 09:51 PM)MikeSD Wrote:  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.

Both the hard configured part of the FORTH and the soft part of the ROM would be on the same module, there isn't room inside the shell of a front plugin for more than one module. The dies for the ROMs are wire bonded directly to the circuit card and then encapsulated with epoxy and it would be possible to have more than one die on the circuit card of a module, in fact they refer to the base RAM and ROM modules as "hybrids" which usually implies there are multiple components involved. The 4K modules used for the base RAM and the 4K plugins are composed of 4 1K dies and the ROM is also 4 dies.

(03-11-2018 09:51 PM)MikeSD Wrote:  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

Yes I think that is what I suggested in one of my last posts, you can tack it onto end of the chain under that resistor where you found it connected on the one you are repairing. You would not want to have a HPIL module plugged in though.

(03-11-2018 09:51 PM)MikeSD Wrote:  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

Sorry for the confusion I was just using the to reference the position of the chip, under what you discovered is the math chip, bottom left, and yes U9 would be a normal 4K module if the original module was still there but in your case that position appears to be occupied by something else since circuit card looks different from the other 4K modules.

The two modules that are bonded together and hanging on the end of wires look like CMT 32K modules that is why I have been referring to them as such and the SOIC package chip on the is a 32KB SRAM which makes it even more likely.

I assure you the entire FORTH module would be a single module.

Paul.