Found these inside a non-working 71B

[Paul Berger (Canada)]

(03-17-2018 09:50 PM)MikeSD Wrote:  

(03-17-2018 08:51 PM)Dave Frederickson Wrote:  [quote='MikeSD' pid='93189' dateline='1521319072']

In the pic in Post #122, there's green stuff between the traces near the top of the long vertical row of vias (holes). That green stuff is battery corrosion.

It might look like corrosion, but without a chemical analysis, I think it's the potting stuff used to bond the surface to the calc. I had a ton of it on the back and it took forever to get it off. It does have a greenish tent to it. But that stuff just wiped off with a little goop remover.



However, the chip may be dead. Here are the connections I used, to connect to my other calc and it froze too, but with the cursor displayed. Pins1-8 and 13 were used.

Since the chip isn't repairable, about the only thing I can do is verify continuity between top and bottom pads, to make sure there isn't any opens there. Looks like the best chip may be belly up, unless there is a necessary missing connection.

Oh wait! I just realized that this was wired as a Port, in my test unit. Ports use pin 10, 11 and 12 also. Pin 12 is tied high though. Any chance those may be causing it not to behave properly as a port device? Wonder if those were also needed when wired into the port zero string? And does the Math also need any of those?

Pin 10 is IR14(Interrupt 14) it would not normally be used by memory devices. Pin 11 is OD in port 1 taking it high disables the internal ROM and is Halt on the rest of the ports this pin would not be used by memory devices except ROMs that take over from the internal OS ROM when plugged into port one such as the diagnostic ROM. Pin 12 is an active low interrupt line. On the plug in modules this pin is normally connected to ground, and if you look at the connectors for the ports you will see a round pad near the outside edge, then a gap and further back the pin would contact a widened ground pin. what this does is cause a momentary interrupt when a module is inserted or removed which notifies the OS so that it can do what it needs to to deal with the event. When you are hard wiring the module in side this pin does not need to be connected to anything.

Off topic, to you have any spare parts for a 71B? I am looking for a top half, it does not need to be functional all I really need from it is the circuit board.

Paul.