|My Battery Sucking HP-71 Memory|
Message #1 Posted by Howard Owen on 22 Sept 2005, 6:20 p.m.
I related elsewhere that I'd purchased an HP-71B that turned out to have a 96KB memory add-on. I told how the calculator would go through batteries at a very rapid clip with the module installed in the card reader bay. I also had verified that this behavior followed the module into a second 71B. At the time, Don W. suggested I post photos of the beast. So here they are. They were all taken through an illuminated magnifying lamp, so please forgive the image quality.
It's an interesting little monster. You can see that one of the screws is missing, because there's a corner of a chip filling the left-hand gap!
The right hand screw hole has a torx head screw too small for any of my tools. I still haven't gotten around to buying an approptiate sized one. But ...
You can do this to the module without unduly straining anything. Here we can see that PCBs have been stacked together, with chips soldered on both sides. The chips at the top in this photo are soldered in the same orientation as the chips on the other side of the board. The other assembly moving down and to the right has a single large chip on one side, mated to two smaller ones below.You can't see it in this photo, but there is another PCB with another five chips underneath the two boards visible here. There was some question in my mind if 96K was really the par RAM amount for this module. Seeing three CBs leads me to think that it is. So assuming it's 32K per board, we must have 4 4K chips and one 16K? How else could it break down? People used to dealing with RAM at the chip level in the same vintage can perhaps enlighten me on that.
Another feature you can sort of see in the above photo is the not-so-great soldering job. The following photo, taken with an additional magnifying glass inline with the first, shows this in more detail:
It is probable that one or more of these joints, or worse ones hidden from view, are responsible for the excessive current drain.
More when I get the right tool to remove the other screw.
Edited: 22 Sept 2005, 6:46 p.m.