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HP-67 - strange behavior - any advice appreciated
06-15-2019, 04:53 PM (This post was last modified: 06-15-2019 05:01 PM by albertofenini.)
Post: #1
HP-67 - strange behavior - any advice appreciated
Hello to everyone,
we have just received an HP67, we posted in the Classified section a WTB request for a logic board
but with no success, so we purchased a unit from TAS.
It was corroded, but pictured ON so we went for it.
As a matter of fact, the logic board was working, so we began our restoration procedure, both aesthetically and on the circuits.
We cleaned everything with a warm mixture of 50% water and 50% vinegar, and when we put all together it was working pretty well.
We have also rebuild the card reader but it was giving a "Error" message with any card.
However, that's the reason why we are writing it stopped to work, quite suddenly.
Or better, when we move the switch from OFF to ON, the display flash for a second a 0.00 or a string of 0.0000000000 then goes off.
You can see a short clip here



It must be also said that there is still some oxidation, very little on the board.

Also, just before to behave so we had this problem : inserting a card in the card reader
didn't turn on the motor, as opposite to when just reassembled that everything
was working correctly (gave Error message but the cards were going thru nicely)
So we checked the switches but nothing, now as a precaution the card reader has been inhibited by putting some tape
between the card reader switches and the keyboard plate, but even with the card reader pcb removed from the logic pcb nothing change

Has it ever happened to someone before ?
What could we check ?
Thanks in advance for any advice you would like to share with us

P.S. we have already check the obvious, switches, cleaned the holes in the logic PCB, battery was fully charged, and it behave equally with the card reader disconnected.

Edoardo & Alberto
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06-15-2019, 11:42 PM
Post: #2
RE: HP-67 - strange behavior - any advice appreciated
Hi Alberto,

Seeing that [0.00] was displayed proves that the CPU worked properly, albeit briefly. Does [000] appear if in W/PRGM mode?

Swapping the CPU board if you have a spare one, would verify the rest of the calculator operation.

Because it was corroded and cleaning seemed to have stopped it working, as a start I would look closely at the circuit board traces, then the battery/board wiring terminations, and the brass link at the charge socket.

All that corrosion probably came from the pcb traces and washing the board may have degraded one (or some) a little more than the circuit can handle. Maybe some "gunk" ended up (or dislodged) under a chip, or a weakened component connection has now become a dry solder joint.

Probably a rarity, but board components can be damaged by static electricity during handling.

cheers

Tony
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