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HP31E Missing Pin
03-13-2021, 07:49 AM
Post: #1
HP31E Missing Pin
Hi all,

I was asled to try and fix a HP-31E. I haven't been inside one before but I assume a pin missing from an IC is not normal.

Hard to image how it went missing except by faulty handling at some stage of its shortened life. It will be somewhat tricky to try and repair it, but perhaps the missing pin caused electrical damage.

The battery ribbon is quite corroded as well near the battery connector which I guess is common.

cheers

Tony


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03-13-2021, 12:12 PM (This post was last modified: 03-13-2021 12:12 PM by AndiGer.)
Post: #2
RE: HP31E Missing Pin
Hi Tony,

Look into this thread - especially last post:

https://www.hpmuseum.org/cgi-sys/cgiwrap...read=24353

Tony Duell mentions pin 8 is the power supply pin on all small IC chips inside a spice. The C models have this IC pin directly connected to PSU / battery to retain RAM content.

Andi
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03-13-2021, 01:51 PM (This post was last modified: 03-13-2021 01:52 PM by teenix.)
Post: #3
RE: HP31E Missing Pin
(03-13-2021 12:12 PM)AndiGer Wrote:  Hi Tony,

Look into this thread - especially last post:

https://www.hpmuseum.org/cgi-sys/cgiwrap...read=24353

Tony Duell mentions pin 8 is the power supply pin on all small IC chips inside a spice. The C models have this IC pin directly connected to PSU / battery to retain RAM content.

Andi

Thanks Andi

Being a power pin the chip (ROM) may have been damaged by not powering up properly while other logic signals are fed to it.

The pin is broken at the point it exits the plastic case so will be hard to attach a wire to.

If anyone knows, I take it that carefully un-clipping the 6 internal plastic retainers (3 on each side of case) will allow more access to innards.

cheers

Tony

cheers

Tony
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03-13-2021, 05:28 PM
Post: #4
RE: HP31E Missing Pin
I had the same missing pin 8 on my HP-33E.

I could attach a wire to it after using a Dremel tool to get more contact area. See this thread Post #9

https://www.hpmuseum.org/forum/thread-3325.html

good luck
Bernhard

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03-14-2021, 03:28 AM
Post: #5
RE: HP31E Missing Pin
Are you talking about opening the spice case?
Iirc you actually need to twist the top and bottom relative to each other. I think it was pre-pandemic when I opened one so can’t recall for sure but I recall it isn’t obvious how it fits together until you take it apart. I don’t remember clips, but if they are just “obvious” I think I got stuck after that; it is the bottom edge (front of the calculator in operating position) that will then be stuck and that is what requires the twist. I think there was something written by Geoff Quickfall that detailed how to open with this technique.-kby
(03-13-2021 01:51 PM)teenix Wrote:  If anyone knows, I take it that carefully un-clipping the 6 internal plastic retainers (3 on each side of case) will allow more access to innards.

cheers

Tony

cheers

Tony
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03-14-2021, 07:42 AM
Post: #6
RE: HP31E Missing Pin
(03-13-2021 05:28 PM)PANAMATIK Wrote:  I had the same missing pin 8 on my HP-33E.

I could attach a wire to it after using a Dremel tool to get more contact area. See this thread Post #9

https://www.hpmuseum.org/forum/thread-3325.html

good luck
Bernhard

Thanks Bernhard,

I managed to do the same - see pic.

I didn't get a battery pack when it was dropped off so have to rely on power supply.

I assume 3V will do. Do you know what polarity the battery terminals are? The battery terminals are on about a 25 degree angle on the small pcb, do you know if the upmost is +ve or -ve?

cheers

Tony


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03-14-2021, 07:46 AM
Post: #7
RE: HP31E Missing Pin
(03-14-2021 03:28 AM)[kby] Wrote:  Are you talking about opening the spice case?
Iirc you actually need to twist the top and bottom relative to each other. I think it was pre-pandemic when I opened one so can’t recall for sure but I recall it isn’t obvious how it fits together until you take it apart. I don’t remember clips, but if they are just “obvious” I think I got stuck after that; it is the bottom edge (front of the calculator in operating position) that will then be stuck and that is what requires the twist. I think there was something written by Geoff Quickfall that detailed how to open with this technique.-kby

The calculator was dropped off with the rear case removed. It looks like the inner plastic moulding is clipped to the top outer case with 6 clips (3 a side) which will have to be prised sideways away from the retainer.

cheers

Tony
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03-14-2021, 08:09 AM
Post: #8
RE: HP31E Missing Pin
(03-14-2021 07:42 AM)teenix Wrote:  I assume 3V will do. Do you know what polarity the battery terminals are? The battery terminals are on about a 25 degree angle on the small pcb, do you know if the upmost is +ve or -ve?

Hi Tony!

The - is closest to the top of the calculator, and + "downwards" to the bottom.
Check this picture:
https://www.hpmuseum.org/batts/bc30.jpg
Ref: https://www.hpmuseum.org/cgi-sys/cgiwrap...read=49445

Cheers,
Thomas

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03-14-2021, 08:18 AM
Post: #9
RE: HP31E Missing Pin
Thanks Thomas :-)

cheers
Tony
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03-14-2021, 10:47 AM (This post was last modified: 03-14-2021 10:48 AM by teenix.)
Post: #10
RE: HP31E Missing Pin
Hi all,

I just had my first experience with the innards of the HP-3x series and I'm sure as others would have found they seem built more around cost than maintenance.

The repaired IC pin did not work when I connected to my power supply - about 2.7V. After removing the inner plastic frame and looking around, the ribbon cable has corroded and split which seems a common fault.

I'll try a fix, but it could be a candidate for Bernhard's repair kit if the owner is interested.

cheers

Tony
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03-14-2021, 04:44 PM
Post: #11
RE: HP31E Missing Pin
(03-14-2021 10:47 AM)teenix Wrote:  Hi all,

I just had my first experience with the innards of the HP-3x series and I'm sure as others would have found they seem built more around cost than maintenance.

The repaired IC pin did not work when I connected to my power supply - about 2.7V. After removing the inner plastic frame and looking around, the ribbon cable has corroded and split which seems a common fault.

I'll try a fix, but it could be a candidate for Bernhard's repair kit if the owner is interested.

cheers

Tony

There is a secret of this chips with missing Pin 8. How could this pin got lost in a soldered version. if it was already broken before the soldering, the calc never could have been released in the wild. And adding the pin did not repair the calc in both cases, mine and yours. Perhaps we don't understand what's going on. Is this pin intentionally missing? Is this a dummy chip, which should not be powered up? The HP-31E does only need two ICs, one ROM one RAM. But why was it assembled at all?

Of course the SPICE LP could repair this calc.

Bernhard

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03-15-2021, 12:16 PM (This post was last modified: 03-15-2021 12:36 PM by ThomasF.)
Post: #12
RE: HP31E Missing Pin
Hi again,

Just checked on my HP-31E, and yes, 2 out of 3 chips (the silvery ones) are both missing pin 8. Doesn't show very well in the picture, but locking close I can see that the pins are missing. My model is the original, clamped version i.e. not soldered, and the pins are really cut, not burnt away.

   

And yes, the device is in excellent condition, works like a charm! Smile

EDIT: Found these notes as well, in this case (a HP32E) only two chips are present - no dummy (without pin 8) was present in this device.
https://www.keesvandersanden.nl/calculat...pair_2.php

Could it be that to keep the correct pressure between the pads and the pins, HP included dummy chips to fill the compartment that are normally used in other models? I also noticed that the chips are marked - in my case only the first chip has readable identification - but the other two was just covered in silver paint.

Cheers,
Thomas

[35/45/55/65/67/97/21/25/29C/31E/32E/33E|C/38E/41C|CV|CX/71B/10C/11C/12C/15C/16C/32SII/42S/28S/48GX/49G/35S/DM41X]
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03-15-2021, 07:10 PM
Post: #13
RE: HP31E Missing Pin
(03-15-2021 12:16 PM)ThomasF Wrote:  Hi again,

Just checked on my HP-31E, and yes, 2 out of 3 chips (the silvery ones) are both missing pin 8. Doesn't show very well in the picture, but locking close I can see that the pins are missing. My model is the original, clamped version i.e. not soldered, and the pins are really cut, not burnt away.



And yes, the device is in excellent condition, works like a charm! Smile

EDIT: Found these notes as well, in this case (a HP32E) only two chips are present - no dummy (without pin 8) was present in this device.
https://www.keesvandersanden.nl/calculat...pair_2.php

Could it be that to keep the correct pressure between the pads and the pins, HP included dummy chips to fill the compartment that are normally used in other models? I also noticed that the chips are marked - in my case only the first chip has readable identification - but the other two was just covered in silver paint.

Cheers,
Thomas
Interesting observation. Have a not working 37e lying around for several years and never realized two chips only with 7 legs. Both 00031 SGP80008.
3rd chip black, no. unreadable
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03-16-2021, 03:32 AM
Post: #14
RE: HP31E Missing Pin
Hi all,

I removed the pin 8 connection again and put a dap of epoxy on the chip where I Dremmelled the plastic away to protect it against moisture ingress.

I repaired the corroded and broken battery ribbon and what do you know, it sprang back to life :-)

cheers

Tony
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03-16-2021, 05:11 AM (This post was last modified: 03-16-2021 05:12 AM by AndiGer.)
Post: #15
RE: HP31E Missing Pin
Congratulations!
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03-17-2021, 09:56 AM
Post: #16
RE: HP31E Missing Pin
(03-16-2021 03:32 AM)teenix Wrote:  Hi all,

I removed the pin 8 connection again and put a dap of epoxy on the chip where I Dremmelled the plastic away to protect it against moisture ingress.

I repaired the corroded and broken battery ribbon and what do you know, it sprang back to life :-)

cheers

Tony

Does it work without the chip? In this case moisture protection is not really necessary?

Bernhard

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03-17-2021, 11:51 AM
Post: #17
RE: HP31E Missing Pin
(03-17-2021 09:56 AM)PANAMATIK Wrote:  
(03-16-2021 03:32 AM)teenix Wrote:  Hi all,

I removed the pin 8 connection again and put a dap of epoxy on the chip where I Dremmelled the plastic away to protect it against moisture ingress.

I repaired the corroded and broken battery ribbon and what do you know, it sprang back to life :-)

cheers

Tony

Does it work without the chip? In this case moisture protection is not really necessary?

Bernhard

I don't know Bernhard, I didn't try. It's not my calculator so best I leave it as is and with the ribbon setup, I think the less handling the better.

It is quite odd that the chip is there in the first place. There are markings under the "paint" on the top surface but I cannot make them out. I couldn't imagine HP just putting them for no reason, and they would have been reasonably expensive in the day.

cheers

Tony
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