41CX halfnut keyboard not responding

[quantalume]

I have the top half of a 41CX halfnut that I bought from a fellow forum member some years ago. At the time, I only needed the enhancement assembly as a donor for another halfnut. I decided to hook up the remaining main PCB to see if it would work. Applying 6 volts between the negative capacitor lead and common diode anode connection, I get MEMORY LOST but then no response from any of the keys including the power switch. Any ideas on how to proceed with troubleshooting? Thanks.

   

[wojtek]

41c service manual would be helpful here, if you find one somewhere I would be interested in having a copy.
As regards your problem if the service manual is not available (and if the time you invest would be worth the result you'll get) perhaps the best approach to localize the problem would be to get hold of another, fully functional unit of 41cx, try to measure the voltages and see the data signals on oscilloscope while operating the keyboards on both units.
Of course you should double check that the main pcb you have is operative.

[ElectroDuende]

(12-06-2015 08:15 PM)quantalume Wrote:  I have the top half of a 41CX halfnut that I bought from a fellow forum member some years ago. At the time, I only needed the enhancement assembly as a donor for another halfnut. I decided to hook up the remaining main PCB to see if it would work. Applying 6 volts between the negative capacitor lead and common diode anode connection, I get MEMORY LOST but then no response from any of the keys including the power switch. Any ideas on how to proceed with troubleshooting? Thanks.

If the attached picture corresponds to the CX we are talking about, it seems to lack the satellite board. I have never tried to operate one without the satellite board, and I don't know it it would be possible, but its a feasible failure cause. Recently somebody suggested in the forum that pat of the CX's ROM may be stored on the satellite board itself.

[Paul Berger (Canada)]

(12-13-2015 02:03 PM)ElectroDuende Wrote:  If the attached picture corresponds to the CX we are talking about, it seems to lack the satellite board. I have never tried to operate one without the satellite board, and I don't know it it would be possible, but its a feasible failure cause. Recently somebody suggested in the forum that pat of the CX's ROM may be stored on the satellite board itself.

The "satellite" board contains the clock, extended functions, and extended memory found in a CX, I do not recall any more if it caused the keyboard to be unresponsive if it was not installed.

Paul.

[wojtek]

I found 41c/cx service manual at http://www.decadecounter.com/vta/pdf2/HP...-90472.pdf
I have only early 41c of 1980 and according to this manual (chapter 3-4) the "satellite" contains Logic PCA. Perhaps on CX there are other circuits there. I have not browsed this document in detail.

[Dave Frederickson]

(12-13-2015 06:10 PM)wojtek Wrote:  I found 41c/cx service manual at http://www.decadecounter.com/vta/pdf2/HP...-90472.pdf
I have only early 41c of 1980 and according to this manual (chapter 3-4) the "satellite" contains Logic PCA. Perhaps on CX there are other circuits there. I have not browsed this document in detail.

That manual and the HP-41C Service Manual can be found on the HP-41 Archive DVD.

[wojtek]

(12-13-2015 06:25 PM)Dave Frederickson Wrote:  That manual and the HP-41C Service Manual can be found on the HP-41 Archive DVD.

Thank you, if only an Archive DVD, kind of, would exist for the 50g...

[rprosperi]

(12-13-2015 06:56 PM)wojtek Wrote:  

(12-13-2015 06:25 PM)Dave Frederickson Wrote:  That manual and the HP-41C Service Manual can be found on the HP-41 Archive DVD.

Thank you, if only an Archive DVD, kind of, would exist for the 50g...

The 50g is still in production, so one cannot expect HP to have released service manuals and other internal stuff, however there is a wealth of info available already, in several places.

All the end-user manuals are available to download from HP

A ridiculously HUGE number of programs are available at hpcalc.org

Many, many gory details have been discussed and documented here in the MoHPC forums

On TAS, you can buy DVDs with most of the above info collected into one place (some also include 48 info)

[jebem]

(12-06-2015 08:15 PM)quantalume Wrote:  I have the top half of a 41CX halfnut that I bought from a fellow forum member some years ago. At the time, I only needed the enhancement assembly as a donor for another halfnut. I decided to hook up the remaining main PCB to see if it would work. Applying 6 volts between the negative capacitor lead and common diode anode connection, I get MEMORY LOST but then no response from any of the keys including the power switch. Any ideas on how to proceed with troubleshooting? Thanks.

Assuming that it should work without the rom/enhanced piggy board at the bottom, I would check the usual stuff in these cases:

- Do a visual inspection for pcb broken traces or shorted ones caused by solder;
- Because the rom/enhanced piggy board was removed, check for good continuity between the copper traces on both pcb sides;
- Are all the keys working well mechanically? Even so, I would destroy all those plastic heat stakes/rivets to inspect the other side of the pcb and make sure no key is stuck;
- A final good cleaning warm distilled water followed by isopropyl alcohol to remove any remaining contaminants can help sometimes.

[quantalume]

Thanks, everyone, for all the helpful replies! As I mentioned, the enhancement module was transplanted to another CX. That other CX worked fine with the bad enhancement module but lacked the X functions and/or time. I will solder in the bad module to this CX and see if it starts responding.

A related question: do you think it's feasible to desolder that 44-pin CPU with hot air, provided I use kapton tape over the heat stakes? I have another CX with a bad LCD that could be a possible donor.

[Nate Martin]

In creating another franken-calculator from many salvaged 41 half nutsssss, the keyboard would not respond until I added the enhanced board...but it is alive! thanks to the hint from this thread.

Now to replace the 470uf capacitor with a thinner version, make the lipo power, and create the no-port 3D printed back shell to birth a true abomination.

[rprosperi]

(03-17-2018 11:37 PM)Nate Martin Wrote:  ...to birth a true abomination.

Please post pics when you complete this super-thin '41 Nate.

Hmmm.....

Coconut... Halfnut... Peanut?

[teenix]

(12-14-2015 06:00 PM)quantalume Wrote:  A related question: do you think it's feasible to desolder that 44-pin CPU with hot air, provided I use kapton tape over the heat stakes? I have another CX with a bad LCD that could be a possible donor.

Probably with a rework solder station. Blowing hot air might damage other components.

A trick I came across recently for desoldering surface mount chips (I think it is on UTube somewhere) uses a Halogen car headlamp. These emit quite a lot of heat and is sufficient to melt the solder. You might be able to mask the plastic part of the chip to protect it a bit. Sunglasses required ;-)

cheers

Tony