Found these inside a non-working 71B

[Dave Frederickson]

(03-17-2018 08:37 PM)MikeSD Wrote:  

(03-17-2018 05:40 PM)Dave Frederickson Wrote:  I believe Raymond made this observation, there's battery corrosion residue on the module. That needs to be removed with a vinegar solution or DeoxIT D100 (red). Check for any shorts between the pins with a meter. Also, its possible that the corrosion may have spread under the encapsulation and this is what killed the calc in the first place.

Dave

No corrosion anywhere. The calc wasn't killed by corrosion. I removed all the mods, fixed a broken display wire and it fired right up. This is a very clean machine, from that respect. There is some residue on the chips but that was the potting stuff they used to bond it into the unit. I've cleaned most of it off.

I have already buzzed from each pin to every other pin, and from pins to ground and power. Only 12 and 13 are shorted together and you can see that in the photo. I have also buzzed to see that there are no cracks or breaks between the pads and any of the via traces to the components. So far all is ok.

I think I might install it in my test unit that is unmodified, and install it in a port position, to see if it works. That eliminates all the other wiring in my original unit. That should tell me if it's working.

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.