My HP-50G Blue dropped dead - The resurrection report

[jebem]

Yesterday, my unique Blue color version of the HP-50G famous calculator was dropped on a desk and stopped working.
The fall was around one meter, from my shaky hands to the desk hard surface.
I can't explain how I did it. Perhaps I'm getting too old for this hobby.

This was a new calculator, in pristine condition, barely used.
120 Euro to the garbage bin, that was my immediate thought.

Inserted 4 batteries and pressed ON.
Well, at least the calculator would turn ON because it beeped after a memory clear, but the display appeared to be totally dead.
No scratches or dents were visible after the accident, and the display looked physically perfect.

As I had nothing to lose, and decided to have a look inside.

Using a suction cup, have removed the plastic screen lens.
This operation requires a small suction cup (see this example by Erwin Ried), no larger than 5cm in diameter, in order to be able to apply extraction force at one of the corners at a time.
I had to apply a few Kg of force in order to be able to lift the plastic lens. This is because the adhesive underneath is very strong.
I have worked one corner at a time, and initially the cover lens didn't move at all, but the adhesive was being slowly broken.
I thought to use an hair drier to apply hot air over the display to soften the adhesive a little bit, but it was not needed.




Have removed the two top self tapping screws, in order to have both halves of the case free to be taken apart.



To take the two halves apart, I used two of my usual pry plastic tools (easy to find them on eBay under repair tools for mobile equipment) to separate them.
Have started at the top side, by inserting the pry plastic tools between the lower white cover and the upper blue cover and sliding the tools towards each corner.
We need to be patient doing this, until the lower cover starts to lift on one of the lateral sides, so have slide the tool along the that lateral side to open the latches (four per side). Then repeated the operation on the other side.
If you try this, please do not use metallic tools on the plastic case as it may leave marks (dents, scratches) of the operation.




A word of caution: Do not separate the two halves apart more than two cm, or the buzzer wires may be broken and the worst case scenario would be a inoperative buzzer if the wire rips off part of the delicate buzzer structure.

Should a wire broke at the buzzer side, a low power (20Watt maximum) iron solder should be used to solder the wire back to the buzzer.
I have just cut the buzzer wires at the PCB side in order to be able to troubleshoot the problem.

Then have removed the RF shield by just peeling it of with caution to not rip it of.

This calculator was never opened before, because the RF shiled was intact.
It is impossible to remove it without breaking it at both sides because it is wrapped around the PCB before the PCB was fixed to the upper case using plastic rivets (and a few self tapping screws as well).




The two PCB components quality is good and up to the current standards in automated manufacture.

However, the assembling of the PCB's really have space for improvement...
The solder joints were left uncleaned of the solder flux/resin, some had that look of badly soldered joints, most probably due to insufficient applied heat to melt the solder with the leads.
Obviously this was a manual assemblage using man power working under pressure with not enough time left to do a better job.

So, because the display failure was caused by a sudden deceleration, and considering the lousy aspect of the solder joints, I used a ohmmeter to check it.
And yes, one of the solder joints was simply broken.
Now, this solder joint was a time bomb waiting to explode any time. The calculator accident just triggered it.



So, I was lucky this time.
Took me 5 minutes to open the calculator. Another 10 minutes to find the fault. And 5 minutes to fix it.
I have used a low power solder iron to fix the joint, then used Isopropyl Alcohol to clean the joints.
After inserting a set of batteries, the display was back to life!

[brickviking]

A very nice story with a happy ending, and well illustrated too. White balancing could have given even better pictures, but the story was told.

(Post 162)

[rprosperi]

(01-27-2018 08:16 PM)jebem Wrote:  So, I was lucky this time.
Took me 5 minutes to open the calculator. Another 10 minutes to find the fault. And 5 minutes to fix it.
I have used a low power solder iron to fix the joint, then used Isopropyl Alcohol to clean the joints.
After inserting a set of batteries, the display was back to life!

Nice rescue Jose!

Thanks for the usual detailed walk-through notes and clear photos. I hope I never will need this information, but it's bookmarked just in case.

Interesting observations that the assembly techniques are both manual and sloppy. Possibly this particular unit didn't pass the standard assembly QC checks and was reworked manually? It's hard to imagine these machines were made by the thousands every week, with such manual techniques.

Does it seem feasible that the broken solder joint (broken upon the fall) was a result of poor assembly, or would a similar fall break such a joint if completed properly?

[jebem]

(01-27-2018 11:21 PM)rprosperi Wrote:  Interesting observations that the assembly techniques are both manual and sloppy. Possibly this particular unit didn't pass the standard assembly QC checks and was reworked manually? It's hard to imagine these machines were made by the thousands every week, with such manual techniques.

Thank you for your feedback, Bob.

IMHO, the 50G has got two PCA's (the processor/keyboard and the display), and both were produced in an automated assembly line due to the components technology in use (SMD insertion is much faster done by a robot than by a human).

However the machine have several more components that are very old style (from the pre-SMD era), and these are manually soldered and routed and taped (battery holder, memory backup capacitor, power supply wires from the two battery holders to the PCA, the buzzer job clearly a manual process too and finished with black tape to cover the buzzer wires solder joints to void a short-circuit on the PCA).

The connection of the two PCA's could be automated, yes, but it was not in my unit. And I can guarantee is was untouched before me, because the RF shield was not broken. So I know this was a standard manufacturing procedure, at least for the batch where my unit came from.

Not that this is a problem by itself. A properly trained operator should be able to solder the interconnect 28 leads in less than 5 minutes including the solder flux removal.
One operator could make at least 80 assemblies per day without working too much.
If you need 1000 per day done, then hire 13 operators for this job. Nothing too much for a manufacturing plant.

Then the installation of the two PCA's inside the case:
- The two PCA's needs to be wrapped with the RF shield, temporally fixed with black tape, and then set on the final position in the upper case where a combination of screws and rivets are used to fix it, and this is a mix of manual processes and automation.

Finally the wiring and installation of the power supply components are clearly a manual procedure, using hard-wiring techniques, and taping the wires to fix them.

I don't see a problem manufacturing thousands of units per week using a mix of robotics and man power. This is what we have been doing along the years, not only in electronic devices but also in other areas like in automobile industry for example.

(01-27-2018 11:21 PM)rprosperi Wrote:  Does it seem feasible that the broken solder joint (broken upon the fall) was a result of poor assembly, or would a similar fall break such a joint if completed properly?

This was a manufacturing defect (cold solder joint), and the fall just triggered the open circuit. The problem would happen even without a fall, given enough time of normal usage (and normal use involves vibration, small "falls" when people put the machine on a desk resulting in some energy that needs to be absorbed as well).
We are talking about a solder joint that, if properly done, is very robust by nature.
The fall could have damaged the LCD itself (it was my fear, really), but that didn't happen because the plastic case is very well designed and built and have absorbed most of the energy.

Edit to add a link.
China assemblage line example where intensive man power (woman power in this case) is used to finish the calculators build.
https://www.youtube.com/watch?v=XZIUDSNzMBo

Edit 2:
I was looking to another 50G and 49G+ internals from other fellows who have been posting in the internet forums, and all look similar to what I have got.
For example, here (not sure if this was published by Han):
http://s1189.photobucket.com/user/_rs1n_...t=3&page=1
Or here (from this MoHPC, by Paul Brogger ) on the identical 49G+:
http://www.hpmuseum.org/cgi-sys/cgiwrap/...i?read=408

Again, this is just my humble opinion on the matter.
But having worked at a manufacturing plant in the 70's (RACAL militar equipemnt and Panasonic consumer electronics) and later in the 90's having big customers like Ford Motor Company Electronics plant in Palmela (Portugal) and later AutoEuropa Ford/Volkswagen manufacturing plant (now it is only Volkswagen), I have been learning a little about manufacturing processes.

[Harald]

(01-28-2018 01:49 AM)jebem Wrote:  

(01-27-2018 11:21 PM)rprosperi Wrote:  Interesting observations that the assembly techniques are both manual and sloppy. Possibly this particular unit didn't pass the standard assembly QC checks and was reworked manually? It's hard to imagine these machines were made by the thousands every week, with such manual techniques.

Thank you for your feedback, Bob.

IMHO, the 50G has got two PCA's (the processor/keyboard and the display), and both were produced in an automated assembly line due to the components technology in use (SMD insertion is much faster done by a robot than by a human).

However the machine have several more components that are very old style (from the pre-SMD era), and these are manually soldered and routed and taped (battery holder, memory backup capacitor, power supply wires from the two battery holders to the PCA).

The connection of the two of the two PCA's could be automated, yes, but it was not in my unit. And I can guarantee is was untouched before me, because the RF shield was not broken. So I know this was a standard manufacturing procedure, at least for the batch where my unit came from.

Not that this is a problem by itself. A properly trained operator should be able to solder the interconnect 28 leads in less than 5 minutes including the solder flux removal.
One operator could make at least 80 assemblies per day without working too much.
If you need 1000 per day done, then hire 13 operators for this job. Nothing too much for a manufacturing plant.

Then the installation of the two PCA's inside the case:
- The two PCA's needs to be wrapped with the RF shield, temporally fixed with black tape, and then set on the final position in the upper case where a combination of screws and rivets are used to fix it, and this is a mix of manual processes and automation.

Finally the wiring and installation of the power supply components are clearly a manual procedure, using hard-wiring techniques, and taping the wires to fix them.

I don't see a problem manufacturing thousands of units per week using a mix of robotics and man power. This is what we have been doing along the years, not only in electronic devices but also in other areas like in automobile industry for example.

(01-27-2018 11:21 PM)rprosperi Wrote:  Does it seem feasible that the broken solder joint (broken upon the fall) was a result of poor assembly, or would a similar fall break such a joint if completed properly?

This was a manufacturing defect (cold solder joint), and the fall just triggered the open circuit. The problem would happen even without a fall, given enough time of normal usage (and normal use involves vibration, small "falls" when people put the machine on a desk resulting in some energy that needs to be absorbed as well).
We are talking about a solder joint that, if properly done, is very robust by nature.
The fall could have damaged the LCD itself (it was my fear, really), but that didn't happen because the plastic case is very well designed and built and have absorbed most of the energy.

Edit to add a link.
China assemblage line example where intensive man power (woman power in this case) is used to finish the calculators build.
https://www.google.pt/url?sa=t&source=we...OD4xbU2nov

The quality of solder joints has become worse since lead free solder is used. Lead free solder joints always look a little like cold joints. So it has become harder to check the quality of the joints.

Cheers,
Harald

[jebem]

(01-28-2018 08:41 AM)Harald Wrote:  

(01-28-2018 01:49 AM)jebem Wrote:  China assemblage line example where intensive man power (woman power in this case) is used to finish the calculators build.
https://www.youtube.com/watch?v=XZIUDSNzMBo

The quality of solder joints has become worse since lead free solder is used. Lead free solder joints always look a little like cold joints. So it has become harder to check the quality of the joints.

Cheers,
Harald

Absolutely true.

Look at the women's speed while doing manual soldering...

I wonder what kind of QA control is was used in the Indonesian and Chinese manufacturing plants sub-contracted by HP to make the 49G+/50G series.
Surely it should include vibration test, considering the young people target market, but most probably it was not systematic.

[aurelio]

thank-you Jose for sharing this nice job, always with detailed pics!!
Happy that your calculator is back to life

I need to buy pry plastic tools asap, my TV remote controls at home are full of dents and marks and actually i did not take with them the same care I have with calculators

[John Smitherman]

Bem feito!

HP is stacking them deep and selling them cheap.


Regards,

John

[jebem]

(01-27-2018 10:01 PM)brickviking Wrote:  White balancing could have given even better pictures, but the story was told.

Yap, I was unhappy with my lousy pictures, but I have realized it too late, after repairing and closing the calculator.
The thing is that my crappy camera is not up to the job (it is very basic), especially when using workbench fluorescent lamps.

(01-28-2018 02:22 PM)aurelio Wrote:  I need to buy pry plastic tools asap, my TV remote controls at home are full of dents and marks and actually i did not take with them the same care I have with calculators

I have just ordered a new set of tools from China, to replace my current worn tools.
In eBay global, I found this kit for just 3 Euro including s&h:
"20 in 1 Mobile Phone Repair Tools Kit Spudger Pry Opening Tool Screwdriver M4F5" from this shop called "onered33".
Note: I have no affiliation with this shop and it's the first time I'm buying from them.
We will see. Most probably it will take 2 months to arrive here, but I can wait.

(01-28-2018 04:10 PM)John Smitherman Wrote:  Bem feito!
HP is stacking them deep and selling them cheap.

Hi, John,
You might have used google translator, didn't you?
I believe I got your message Thanks!


Thank you all for the feedback!

[aurelio]

(01-28-2018 04:11 PM)jebem Wrote:  I have just ordered a new set of tools from China, to replace my current worn tools.
In eBay global, I found this kit for just 3 Euro including s&h:
"20 in 1 Mobile Phone Repair Tools Kit Spudger Pry Opening Tool Screwdriver M4F5" from this shop called "onered33".
Note: I have no affiliation with this shop and it's the first time I'm buying from them.
We will see. Most probably it will take 2 months to arrive here, but I can wait.
Thank you all for the feedback!

Jose thank-you for the links and don't worry, nobody here should think that you have affiliation with that shop

I'm not worried for the time, but just because buying from China means to pay fees higher the the item price

[jebem]

(01-28-2018 07:00 PM)aurelio Wrote:  

(01-28-2018 04:11 PM)jebem Wrote:  I have just ordered a new set of tools from China, to replace my current worn tools.
In eBay global, I found this kit for just 3 Euro including s&h:
"20 in 1 Mobile Phone Repair Tools Kit Spudger Pry Opening Tool Screwdriver M4F5" from this shop called "onered33".
We will see. Most probably it will take 2 months to arrive here, but I can wait.

I'm not worried for the time, but just because buying from China means to pay fees higher the the item price

Well, that's the risk I take everytime I order goods from outside European Union.
But at 3 Euro inc. s&h, I'm sure Portuguese Customs can't charge any import duties.
The maximum order value free of taxes is 15 Euro if I'm not wrong.
Customs will however hold the package for at least 3 weeks.
That is why i mentioned 2 months for delivery ( 1 month in transit to enter EU, and then Customs will do their "thing" trying to get some money from the citizens in order to pay the bills of the public servants.