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HP 41C TALL KEYS repairing questions
09-27-2014, 03:31 PM (This post was last modified: 09-27-2014 03:46 PM by jebem.)
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RE: HP 41C TALL KEYS repairing questions
(09-27-2014 11:24 AM)aurelio Wrote:  May you tell me if to remove the keyboard needs to cut just the plastic rivets (unfortunately a lot) and how may I restore it (glue?);

Hi Aurelio,

From what I have been reading, these machines are a pain to maintain and that's why I didn't got one to join my collection.

On the positive side, You mentioned that you had the batteries removed from the calculator, perhaps for long time.
This is good news (for me at least) because there are some nasty little things inside the calculator called electrolytic capacitors that may degrade themselves with time, specially if they stay long time without energy.

1. KB assembly removal:

I was checking the Service Guide (from the MoHPC DVD set) and in fact HP do not offer a procedure to remove the keyboard Sad
This 41 series shares this fixing plastic rivets manufacturing technique with many other models like the 20's, 28's, 48's and so forth.

Apparently the only solution is to destroy the original rivets shape by heating them (maybe a iron solder?) so they melt enough to remove the KB assembly.
In this way it should be possible to reuse the rivets by heating them again, even if we would need to add some strong glue to help the rivets to fix the assembly in place.

I'm sure there are experts here that may offer help based on previous experience on this model.

2. Power On delay/laziness/not working

From what I read in the service guide and in the old forums, this symptom can have several possible causes, starting by defective contacts on the connection between the kb assy and the processor assy, or a possible power supply failure.

First thing, make sure there are no excessive current consumption from the 6V batteries.
And check CR1, CR5 and CR6 protection diodes, just in case.
While you are there, check C1 as well.

Next, verify the cpu reset circuit around U2 Power Supply IC.
Check proper voltage at Vin/Vbat (input voltage to U2), and at Vcc (output voltage from U2).
Page 4-13 of the service guide can be followed here for details.

Check the capacitor C9 and Transistors Q1 and Q2.
And check C3 and C10 just in case.
If nothing found, I would check all the components around U2 IC, including the T1 inductor for good continuity.

Just a word of caution, it is easy to damage a good component when removing it (using a iron solder) by overheating. Good soldering technique is a requirement here.

Luiz Veira was a very active MoHPC contributor in the old forum. Here some nice photos concerning the LCD removal.

Good luck with your repair, and please share your work here.

Jose Mesquita member

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RE: HP 41C TALL KEYS repairing questions - jebem - 09-27-2014 03:31 PM

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