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HP-65 1605A02841 - weird display and card reader issues
11-15-2020, 12:01 AM
Post: #9
RE: HP-65 1605A02841 - wrong display behavior
Hi everyone, a couple of updates ...

Since we weren't able to fix a lcd/keyboard from another unit described in this post HP-65 1603S03504 - display not working at all
we decided to use one of those led block to replace the first one of this unit which was defective

After that the decimal point started to work correctly
However all the C segments C where still on.
We found out that this happens with this logic board and any led/keyboard is paired with.

On the contrary, when a working logic board is paired with this led/keyboard everything works fine, both the decimal point and the C segment behave like they should.

Then We have taken some snapshot of the Disp0, Disp1, Disp2, Disp3, Disp4 and RCD signals from both a working logic/led/keyboard and this unit looking for differences.
Waves in red are from this unit waves and waves in blu are from a working assembly.

We noticed that this logic board has a different Disp0 and a different RCD from a known working unit .

Any idea if this is fixable and how ?

Also we completed the restoration with a card reader
However, while it reads consistently well, RA and RB are clean as they should
it doesn't write correctly and in fact WA and WB are not in good shape.

What are the odds that the sense amplifier is faulty or the head is faulty ?

Please note that for the card reader, blu and red waves are from the same unit
Thanks in advance for any idea you may want two share

Updated pictures : HP-65 1605A02841 - wrong display behavior updated album

Edoardo & Alberto
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RE: HP-65 1605A02841 - wrong display behavior - albertofenini - 11-15-2020 12:01 AM



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