Found these inside a non-working 71B

[MikeSD]

(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?