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Found these inside a non-working 71B
03-11-2018, 07:31 PM
Post: #26
RE: Found these inside a non-working 71B
(03-11-2018 06:09 PM)MikeSD Wrote:  Dave,

Yes i'll post label and back side of F/A, if that is what it is. The chip p/n above U9 is shown above.


it's out. that chip above U9 seems soldered ok. Just thin wires so it moves. Buzzes ok top to bottom.

Now to the cleanup. Step by step.

My original problem: Calc wouldn't power on. No LCD content displayed at all.

My assumption was it might have had something to do with broken wires in these new chips. Assuming that the broken wires didnt touch something else it shouldnt, can not being able to configure these chips break the chain so that nothing would show on display?
The way that is wired it should not it looks loke they broke into the chain at the end so the only thing that would not work is the HP-IL. You can check the chain U6 Din is connected to +5V, U6 Dout to U7 Din U7 Dout to U8 Din U8 Dout to U9 Din (bottom of two Roms ) U9 Dout to Din of top ROM. your picture showing the edge on vie confirms that Dout from the top ROM is where the RAM and "FORTH" modules are inserted. The OS ROM is hard addressed and is not part of a chain.

(03-11-2018 06:09 PM)MikeSD Wrote:  I'm now wondering if these mods might not have anything to do with the lack of LCD.

The repair label said the original problem in 86 was CPU lockup. That appears to have been repaired. If the 71B doesnt run after removing my RAM and FORTH, I might switch 71B.
It might be useful to test them in a working 71B what you could do is parallel the first 7 pins and ground with one of the ROMs and with no HPIL module installed connect Din to the end of the chain there is at least one via in the signal path to the HPIL module or you can find it on pin 8 of the empty top connector. There is a via that might be easy to pick up the signal from just under a 10K resister just below the 00071-80002 BD. NO., I think that would be the easiest spot to pick up the signal.

I had made up a plug in to bring out those 7 signals plus ground to the front to monitor the bus with a logic analyzer, but now it is coming in handy when I am testing some RAM modules.

(03-11-2018 06:09 PM)MikeSD Wrote:  Question on replacing flex cable. There are two pins connected together on one end on bottom board, but on the display side the outside pin doesnt have a trace or via to it. But does have a trace in the flex for it. Why is that? and/or what is that pin for?

That is the ground pin and on my spare it looks like there was the same number of pads at both ends (Some pads damaged at the CPU end) but it does not look like the outermost pad was connected but they may have been solder bridged.
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Messages In This Thread
RE: Found these inside a non-working 71B - Paul Berger (Canada) - 03-11-2018 07:31 PM
What's U10? - Dave Frederickson - 03-15-2018, 03:43 PM

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