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broken HP65...help!
04-04-2021, 04:18 PM
Post: #1
broken HP65...help!
My son inserted a magcard in the reader, which I had firmly forbidden him to (since I assumed that the rubber wheel was in very poor condition...) I use this HP65 as a calculator only, and never use the magcards... Anyway, the calculator motor started, grabbed hold of the magcard that got stuck and there was a terrible squeek, as from a dying animal. He turned power off, and just with some force, pulled out the magcard backwards.

Now the calculator is far from dead, but totally crappy. Turning it on, you will get any random number/numbers in the display, flickering digits, sometimes even "counting fast upwards". But sometimes (one out of ten) it looks correct, and I can even enter a correct digit, sometimes two or more. Turning the calculator off/on and repeating this process, the behavior "improves" very, very slowly, and after 100 times I can actually enter many correct digits.

I have opened the HP, hoping to find some burned component, but nothing visually.
Also I am very good with electronics in general, fully equipped for replacing circuits (even surface mounted which of course we have not here).

Logically... I drew out an awful amount of current to the motor. Assuming the large chip doing the motor control / card reader stuff broke down, would this disrupt the "normal function" of the calculating functions?

So what are your thoughts? I have no schematics, and honestly very low knowledge of how the HP65 is built up. What DC voltage can I check, and where are the "> 3.6V voltages" generated? Is there any specific resistor/diode/capacitor the may have broken during this fatal seconds I described above?

Very thankful for all suggestions...
/Richard
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04-04-2021, 06:33 PM (This post was last modified: 04-04-2021 06:38 PM by AndiGer.)
Post: #2
RE: broken HP65...help!
In this post you find a link to a helpful pdf file:
https://www.hpmuseum.org/forum/thread-10...#pid114759
Maybe helpful.

Tell us pls.: Was the calculator operated from batteries or from the charger only when the card was inserted?

Andi

Edit: Welcome on board :-)
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04-04-2021, 06:50 PM
Post: #3
RE: broken HP65...help!
It was running on batteries only. I remember it well.
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04-04-2021, 07:04 PM
Post: #4
RE: broken HP65...help!
Wow! Found the "hp65repair.pdf" via the link you sent. Looks like a goldmine for me!
Thanks a lot !!!
/Richard
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04-04-2021, 09:08 PM
Post: #5
RE: broken HP65...help!
What's the best way to test a card reader, that hasn't seen any action in decades?
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04-04-2021, 10:21 PM
Post: #6
RE: broken HP65...help!
According to my teen son, obviously just insert a card.... :-)
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04-05-2021, 12:07 AM (This post was last modified: 04-05-2021 12:09 AM by teenix.)
Post: #7
RE: broken HP65...help!
This is only speculation, but if the motor stalled while trying to read the card, excess current may have been drawn and damaged the sense chip. This may be causing improper operation.

You might try unplugging the card reader circuit board from the CPU board and see if the calculator operation improves.

The motor power is drawn directly from the battery through the sense chip, so I wouldn't expect the CPU board to be damaged.

cheers

Tony
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04-05-2021, 12:15 AM
Post: #8
RE: broken HP65...help!
(04-04-2021 09:08 PM)dhe Wrote:  What's the best way to test a card reader, that hasn't seen any action in decades?

Check the condition of the card reader circuit board for corrosion and the condition of the card drive mechanism and repair it if it has perished into the "gummy wheel".

Be careful with disassembly as there are some small parts that love to hide when disturbed.

cheers

Tony
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04-05-2021, 05:48 AM
Post: #9
RE: broken HP65...help!
(04-05-2021 12:15 AM)teenix Wrote:  .....[omissis]......
Be careful with disassembly as there are some small parts that love to hide when disturbed.

cheers

Tony

jumping springs and rolling balls Smile
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04-05-2021, 06:59 AM
Post: #10
RE: broken HP65...help!
... with this hobby consider at least 30 per cent of the time spent on the carpet looking for small parts ...
(04-05-2021 05:48 AM)aurelio Wrote:  
(04-05-2021 12:15 AM)teenix Wrote:  .....[omissis]......
Be careful with disassembly as there are some small parts that love to hide when disturbed.

cheers

Tony

jumping springs and rolling balls Smile

Edoardo & Alberto
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04-05-2021, 07:08 AM
Post: #11
RE: broken HP65...help!
Hi everyone
Can you post some pictures ?
I would follow Teenix and the other people advices, all of them have been of great help in assisting us when repairing our HP65s
But let me add something not electronically related
Repair it with your son
I did it with mine and we have such a good time together at the bench
When it will be repaired you will see such a satisfying look in his face
And if I can add something don’t just try to bring it back as it was before
Try to repair the card reader making it at least reading cards
Today’s teenagers use terabytes as the minimum capacity size even for their PlayStation
But you will be surprised how amazed he will be when few bytes will be successfully read from a tiny card
Good luck with your repair !!!

Edoardo & Alberto
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04-08-2021, 10:16 PM
Post: #12
RE: broken HP65...help!
I will agree with teenix’ suggestions, but I wouldn’t be too hard on your son. Usually with a gummy wheel or otherwise jammed card something else breaks: the gummy wheel disintegrates or the clutch breaks, etc., rather than real electrical damage. Perhaps corroded barely contacting fingers got barely moved, but enough to break a weak contact.-kby
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04-30-2021, 03:55 PM
Post: #13
RE: broken HP65...help!
Thank you to all nice people with ideas and links to interesting information!

The HP65 is working now. It was an unusual(?) error I think....

Inside the card reader there are four small plastic balls, the purpose is to press the card against the reader head during the read operation.
And then there is a five finger metal flap, working as the "springs" for these four balls (the fifth finger is ground I guess, always connected to the circuit board.)

One of these four plastic "balls" was full of goo from the more or less floating rubber (or polyeurathane) wheel. And was stuck in this position. Then the "backside" of this finger was in permanent contact with the circuit board. I guess this is some kind of "inhibit" function, re-arranging some functions for the cpu, during the read-card operation.

So cleaning up the mess here, so all four plastic balls, and the four metal fingers could go back to the "off"-position, did the trick !

Once again, thank you all for you interest in my post!
/Richard
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