HP 32SII success and woes

[Sanjeev Visvanatha]

Question regarding untwisting the twist clips. What is the best tool for this? It seems that flat nose pliers would be best. Do they need to have the nylon covers?

My next step is to remove the PCB and see what I can find out. I may try a board swap with my 10B guinea pig.

[Sanjeev Visvanatha]

Regarding the 'metal plate' I was mentioning earlier. It seems that with the introduction of the 32SII in 1991, HP went to a PCB design with ground shield mesh on the back, eliminating the need for metal shielding on the back of the calculator case.

http://www.hpmuseum.org/guest/brogpion.htm

Quote:With the HP-32SII and newer low-end models, HP has greatly simplified the PCBs' layouts. The new PCBs have traces on only the front side, with a ground shield mesh on the back. (This has eliminated the need for metal shielding in the back of the calculator.)

So, I surmise that the metal plate I was referring to is the shielding on the inside of the case found pre-1991 on all models and post-1991 on everything but the 32SII and low end models.

This seems to be supported by Fig. 23 of Geoff's article, where the metal shielding covers the exact spot I was referring to in my previous posts:

http://h20331.www2.hp.com/hpsub/download...e_2010.pdf

(Click on Calculator Restorations when the PDF opens up)

[rprosperi]

(02-13-2015 12:17 PM)Sanjeev Visvanatha Wrote:  Regarding the 'metal plate' I was mentioning earlier. It seems that with the introduction of the 32SII in 1991, HP went to a PCB design with ground shield mesh on the back, eliminating the need for metal shielding on the back of the calculator case.

http://www.hpmuseum.org/guest/brogpion.htm

Quote:With the HP-32SII and newer low-end models, HP has greatly simplified the PCBs' layouts. The new PCBs have traces on only the front side, with a ground shield mesh on the back. (This has eliminated the need for metal shielding in the back of the calculator.)

So, I surmise that the metal plate I was referring to is the shielding on the inside of the case found pre-1991 on all models and post-1991 on everything but the 32SII and low end models.

This seems to be supported by Fig. 23 of Geoff's article, where the metal shielding covers the exact spot I was referring to in my previous posts:

http://h20331.www2.hp.com/hpsub/download...e_2010.pdf

That final link appears to be bad, it takes me to some sales page on HP's website. I think the ellipsis screws it up.

[Sanjeev Visvanatha]

(02-13-2015 12:51 PM)rprosperi Wrote:  That final link appears to be bad, it takes me to some sales page on HP's website. I think the ellipsis screws it up.

Fixed my post above. Thank you.

[rprosperi]

(02-13-2015 01:01 PM)Sanjeev Visvanatha Wrote:  

(02-13-2015 12:51 PM)rprosperi Wrote:  That final link appears to be bad, it takes me to some sales page on HP's website. I think the ellipsis screws it up.

Fixed my post above. Thank you.

The link that looks like this:
http://h20331.www2.hp.com/hpsub/download...e_2010.pdf

still takes me here: http://www8.hp.com/us/en/ads/clientmanag...rview.html

[Sanjeev Visvanatha]

(02-13-2015 06:53 PM)rprosperi Wrote:  The link that looks like this:
http://h20331.www2.hp.com/hpsub/download...e_2010.pdf

still takes me here: http://www8.hp.com/us/en/ads/clientmanag...rview.html

The link in post 22 was updated earlier today, and works for me..... strange.

[Sanjeev Visvanatha]

OK, I performed some surgery today and some transplanting.

I removed the PCB using flat nose mini pliers to untwist the clips holding it down. I cleaned the zebra strips and contacts with isopropyl alcohol. After careful reassembly, I was still presented with the same issue of gibberish on the screen.

Then, I removed the PCB and LCD from the 10B, and transplanted the PCB and LCD from the 32SII into the 10B front body. After carefully reassembling, I ran the self test, and was still presented with the same gibberish. This precludes the layered keyboard assembly of the 32SII being the culprit.

I now conclude that that something on the PCB is to blame. I used a magnifying glass to carefully examine all traces, the pins for the IC and did not see anything wrong.

I have managed (on occasion) to get the calculator working normally, for short periods after removing the batteries and draining the capacitor. But after a short time, the calculator reverts back to the weird display of characters. I noticed that there is a 10uF capacitor on the PCB next to the positive battery terminal. My last hunch is that the capacitor is faulty. I know blown capacitors in electronics can cause all sorts of strange issues. This is only a hunch, and probably the last thing I can think of that I could try on my own.

Thanks for all the help. I opened up 2 Pioneers last night for the first time, and now know how to remove the PCB and clean the contacts, etc. So the learning experience has been invaluable. I just wish I could have gotten the 32SII working in the process.

[rprosperi]

(02-14-2015 04:27 AM)Sanjeev Visvanatha Wrote:  The link in post 22 was updated earlier today, and works for me..... strange.

And now it works for me too. Even stranger... Thanks!

[ElectroDuende]

(02-14-2015 04:44 AM)Sanjeev Visvanatha Wrote:  I noticed that there is a 10uF capacitor on the PCB next to the positive battery terminal. My last hunch is that the capacitor is faulty. I know blown capacitors in electronics can cause all sorts of strange issues. This is only a hunch, and probably the last thing I can think of that I could try on my own.

My next recommendation was going to be that. To replace any capacitor you can find there. As far as I know it is not a usual problem on HP machines, but the aging of electrolytic capacitors is one of the most usual causes of failure in electronic equipment. Other capacitor types are less prone to failure, but the cost of them is so low, that it worths to try...

[Bruce Larrabee]

You say the calc operates normally if you connect the 'twisty' to ground? I had a calc
recently that had a poor contact with the 'twisty' to PCB ground path. It was dead. Never saw this before. A little solder on the pads near one of the 'twisty' solved it.

Also I think the capacitor is tantalum.

[jebem]

(02-14-2015 04:44 AM)Sanjeev Visvanatha Wrote:  Then, I removed the PCB and LCD from the 10B, and transplanted the PCB and LCD from the 32SII into the 10B front body.

I now conclude that that something on the PCB is to blame. I used a magnifying glass to carefully examine all traces, the pins for the IC and did not see anything wrong.

Hi, Sanjeev ,
Thank you for sharing your experience with your new HP-32SII.

I have two working HP-32SIi, so I'm not in the mood to open them, considering the fact that the process will destroy the original integrity.
But I'm curious about the machine internals...

So, may I ask you some additional information?

- Did the LCD display came out easily along with the zebra strips?

- Can you identify a small component in the lower left corner, close to the spring contact? From this site, it looks like a smd resistor.

Additional information:
I found excellent Lyuka article showing details here. It looks like the smd resistor is a jumper after all (value=000). Can someone confirm this?


You and others here have done a excellent differential diagnosis, and apparently the possible root causes are now:

- The PCA copper shield is not electrical connected to one of the 6 twisting metal clips as it should. This is MOS technology, and this machine uses large amounts of metal plates that must be grounded to minimize electrostatic fields that can interfere with the SoC (system on a Chip).

- The PCA itself. Well, from the available photos, one can see only 3 components: the NEC SoC, a smd 10uF 16VDC Tantalum capacitor, and a smd resistor.
I would start by replacing the capacitor and then replace the resistor.

Now, the real challenge here is to find out the correct value of it.
Can you identity the printed numbers on it?
Also, if you have access to a multimeter, please try to measure it in circuit; take two readings, first using positive probe on the left side of the resistor, second reading using the positive probe on the right side.
(of course all this must be done after removing the batteries and short-circuiting the 10uF capacitor for at lest 1 minute).

EDIT:
if you get a infinite or a very high reading, most probably the resistor is in open circuit. From what I can see in the photos, this resistor is connected to the ground spring connector.
If this is true (you may check this with a multimeter), that can very well explain the issue.
In that case, I would carefully add an additional 10Kohm resistor in parallel with the smd resistor, by soldering it to the existing smd resistor terminals.
This is a tricky operation, requiring a steady hand a proper soldering iron for this kind of work.

Thank you!

[Sanjeev Visvanatha]

(02-15-2015 04:21 PM)Bruce Larrabee Wrote:  You say the calc operates normally if you connect the 'twisty' to ground? I had a calc
recently that had a poor contact with the 'twisty' to PCB ground path. It was dead. Never saw this before. A little solder on the pads near one of the 'twisty' solved it.

Also I think the capacitor is tantalum.

On further examination, the entire ground shield appears to have good contact with the twistees. I confirmed this with reading voltage from positive terminal to ground shield in several places. It reads the exact value of the battery voltage.

[Sanjeev Visvanatha]

(02-16-2015 09:36 AM)jebem Wrote:  ...

So, may I ask you some additional information?

- Did the LCD display came out easily along with the zebra strips?

-Yes, the zebra strips come out very easily. I used some plastic pliers to carefully remove them.

-The method I used to remove the LCD was to push it from the front of the calculator to the back of the calculator. You do this with the PCB and zebra strips removed. It is held in with a strip of 2 sided tape on the top and bottom edges. If you apply even force, it will start to tear, and you hear the adhesive coming apart. When doing this, be very careful to apply opposite pressure at the right places to the frame of the unit so as to avoid any permanent deformation of the front face.

(02-16-2015 09:36 AM)jebem Wrote:  - Can you identify a small component in the lower left corner, close to the spring contact? From this site, it looks like a smd resistor.

Additional information:
I found excellent Lyuka article showing details here. It looks like the smd resistor is a jumper after all (value=000). Can someone confirm this?

-My unit has the PCB back in place, and I am not sure how many more attempts I will have to untwist them. I did see both of these links in my research. I do not believe that the small SMD component next to the spring contact had any marking on it.

(02-16-2015 09:36 AM)jebem Wrote:  You and others here have done a excellent differential diagnosis, and apparently the possible root causes are now:

- The PCA copper shield is not electrical connected to one of the 6 twisting metal clips as it should. This is MOS technology, and this machine uses large amounts of metal plates that must be grounded to minimize electrostatic fields that can interfere with the SoC (system on a Chip).

- I can confirm that the electrical contact between twistees and the ground shield is there.

(02-16-2015 09:36 AM)jebem Wrote:  - The PCA itself. Well, from the available photos, one can see only 3 components: the NEC SoC, a smd 10uF 16VDC Tantalum capacitor, and a smd resistor.
I would start by replacing the capacitor and then replace the resistor.

Now, the real challenge here is to find out the correct value of it.
Can you identity the printed numbers on it?
Also, if you have access to a multimeter, please try to measure it in circuit; take two readings, first using positive probe on the left side of the resistor, second reading using the positive probe on the right side.
(of course all this must be done after removing the batteries and short-circuiting the 10uF capacitor for at lest 1 minute).

EDIT:
if you get a infinite or a very high reading, most probably the resistor is in open circuit. From what I can see in the photos, this resistor is connected to the ground spring connector.
If this is true (you may check this with a multimeter), that can very well explain the issue.
In that case, I would carefully add an additional 10Kohm resistor in parallel with the smd resistor, by soldering it to the existing smd resistor terminals.
This is a tricky operation, requiring a steady hand a proper soldering iron for this kind of work.

Thank you!

- I will have to remove the PCB again to do this. Soldering in new resistor as suggested may be difficult for me to do, as I am not very good at that type of work. I can make the checks and then report back, including noting any markings I see.

[Sanjeev Visvanatha]

(02-16-2015 09:36 AM)jebem Wrote:  You and others here have done a excellent differential diagnosis ....

Thank you for your help. To add to the differential diagnosis, I stumbled upon the following:

- The calculator works fine (with low batt indicator on) if only 2 of the LR44 batteries are used. A 3V 32sii? I am not an electronics person, so this is another qualitative data point I have on the subject.

- Would this support the resistor being open?

[Sanjeev Visvanatha]

(02-16-2015 09:36 AM)jebem Wrote:  Additional information:
I found excellent Lyuka article showing details here. It looks like the smd resistor is a jumper after all (value=000). Can someone confirm this?

Indeed, it does look like a jumper if you examine the traces in that area. I did notice that when I had the PCB removed as well.

[jebem]

(02-16-2015 02:33 PM)Sanjeev Visvanatha Wrote:  - The calculator works fine (with low batt indicator on) if only 2 of the LR44 batteries are used. A 3V 32sii? I am not an electronics person, so this is another qualitative data point I have on the subject.
- Would this support the resistor being open?

Now, that is interesting information!
If the problem lies inside the SoC, for instance with a few bad logic gates, then it is probable that varying the power supply up or down can allow these gates to start switching in sync with the rest of the circuitry.
If you have access to a laboratory adjustable regulated power supply, it was interesting to find out at what voltage level does it start misbehaving.

But it seems that this resistor is in fact a jumper, as its label has the value "000" (Zero Ohm) connecting the circuit to the metal plate using that spring connector.
The jumper is there for a reason, so if you can take the risk to untwist/twist once again the 6 metal clamps, I believe it is worth the try.

PS - Thank you so much for your previous information regarding the LCD display removal.

[Bruce Larrabee]

he capacitor is 10.6 µF.

[Sanjeev Visvanatha]

(02-17-2015 12:26 PM)Bruce Larrabee Wrote:  he capacitor is 10.6 µF.

The capacitor is marked as follows on the photo here.

106
16k

I interpret this as 10*10^6 pf and 16V ±10%

[jebem]

(02-17-2015 01:16 PM)Sanjeev Visvanatha Wrote:  The capacitor is marked as follows on the photo here.

106
16k

I interpret this as 10*10^6 pf and 16V ±10%

1+

It's a nominal value of 10,000,000 pF, or 10,000 nF, or 10uF.

Of course the real value needs to be measured and usually it can be a little bit higher when we talk about electrolytic capacitors (not the case here, as this one here looks like a Tantalum type).

[Sanjeev Visvanatha]

(02-16-2015 09:36 AM)jebem Wrote:  Now, the real challenge here is to find out the correct value of it.
Can you identity the printed numbers on it?
Also, if you have access to a multimeter, please try to measure it in circuit; take two readings, first using positive probe on the left side of the resistor, second reading using the positive probe on the right side.
(of course all this must be done after removing the batteries and short-circuiting the 10uF capacitor for at lest 1 minute).

There are no markings on the SMD resistor. It is a jumper as we have concluded before.

The capacitor is marked 106 16k, the same as the HP 10B I have and the link quoted above.

I only have access to an analog multimeter. With it set at 10x, the resistance of the jumper reads ~0.0 Ohms.

The resistance across the capacitor reads about 16 Ohms.

The resistance across the same spec capacitor on the HP 10B PCB I have is 17.5 Ohms.

(02-16-2015 09:36 AM)jebem Wrote:  Now, that is interesting information!
If the problem lies inside the SoC, for instance with a few bad logic gates, then it is probable that varying the power supply up or down can allow these gates to start switching in sync with the rest of the circuitry.
If you have access to a laboratory adjustable regulated power supply, it was interesting to find out at what voltage level does it start misbehaving

I do not have access to a power supply.

Can I test the capacitor further with a basic analog multimeter?