Threaded Mode | Linear Mode

aj04062 · 03-19-2016, 01:23 AM

I am trying to fix a HP-70 for a fellow enthusiast. The symptoms are:
Several keys such as /, O and . Do not register correctly. For example the decimal key is interpreted as the change sign key.

To rule out corrosion or something else on the keyboard, I paired up a 45 motherboard to the keyboard. With this combo it works as it should.

So, this leads me to conclude it is the 70 motherboard. But what chip has failed? A common one or one unique to the 70?

Geoff Quickfall · (This post was last modified: 03-19-2016 02:00 AM by Geoff Quickfall.)

Check out this posting, mine is now running perfectly:

http://www.hpmuseum.org/forum/thread-4989.html

Geoff

aj04062 · (This post was last modified: 03-19-2016 12:40 PM by aj04062.)

That doesn't line up with this units malfunction. It's as if it is interpreting the wrong row and columns.
Divide = Add
zero = TBD
decimal = CHS
CLX = M+

You can see I almost have a row to row confusion here, but not quite. BTW, the row with enter CHS and M+ work fine.

Would that likely be a failing CTC Chip?

Geoff Quickfall · 03-19-2016, 07:13 PM

No, not a ram problem, just lots of info on the chip set.

How about corrosion on the motherboard?

How did the 70 mother board work in the 45 keyboard?

Inspect the mother board, especially around the chip set solder points and traces. Resolder the chip set especially around the ROMs. A motherboard wash/rinse with warm vinegar followed by water then anhydrous alcohol. Inspect the traces. Test when dry.

Geoff

aj04062 · 03-19-2016, 07:27 PM

I cannot see any corrosion on the motherboard.

I did not swap the other way.

I'll give the 70 board a vinegar bath. Thanks!

Geoff Quickfall · 03-19-2016, 08:45 PM

Just ruling out mechanical issues before diving into the ARC chip.

Cheers, Geoff.

aj04062 · 03-27-2016, 12:01 PM

I have cleaned and re-flowed solder with no luck.

Is the only source of this behavior the CTC or could ROM cause this too?

aj04062 · 04-10-2016, 02:50 AM

Update: a successful transplant of a good CTC chip has cured this 70 of its issues

**Katie Wasserman** · 04-10-2016, 03:19 AM

It's good to hear that, another saved classic!

TASP · 04-10-2016, 06:09 AM

Indeed.

Salute !!!

Geoff Quickfall · 04-10-2016, 05:21 PM

Excellent.

Massimo Gnerucci · (This post was last modified: 04-10-2016 05:41 PM by Massimo Gnerucci.)

(04-10-2016 05:21 PM)Geoff Quickfall Wrote: Excellent.

(04-10-2016 05:25 PM)Geoff Quickfall Wrote: Excellent.

Incorrect key registering for you too?

Smile

Geoff Quickfall · (This post was last modified: 04-11-2016 12:48 AM by Geoff Quickfall.)

Ha,

No idea why the double. Maybe virtual key bounce :-)

For continuities sake, Massimo is referring to a double post, the second of which I have deleted.

TASP · 04-11-2016, 03:23 AM

LOL !!

Always appreciate the humor, and a successful repair of a classic calculator is certainly cause for celebration and levity.