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Found these inside a non-working 71B
03-17-2018, 08:37 PM (This post was last modified: 03-17-2018 08:41 PM by MikeSD.)
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RE: Found these inside a non-working 71B
(03-17-2018 05:40 PM)Dave Frederickson Wrote:  
(03-17-2018 03:32 AM)MikeSD Wrote:  Here is the FORTH Assembler Module. I can't see anything out of the ordinary. Wonder if there was some jumper that was present that got removed when this was cleaned up.

Anyway, when 1-7, 8 and 13 are used, the system won't power up. I'll be checking voltages tomorrow.

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.


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.
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What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM
RE: Found these inside a non-working 71B - MikeSD - 03-17-2018 08:37 PM

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