testing a 41cv before attempting lower post repair

[dmh]

I've received a 41cv that looks in pretty good condition but has cracked lower posts which look like they have been repaired before.

Before I attempt the same repair for the first time I was wondering if removing the post screws and holding the top and bottom of the calculator together firmly and inserting batteries would be a reliable test?

I want to make sure it actually works before attempting the repair and wondering if this would be a reliable test or not.

The lower zebra connector and the module/battery connector look in good condition.

Regarding the post repair, I've seen a few different articles about gluing the post but given how they look now do I have to break the pieces off to insert glue between the pieces? See attachments.

Or is the larger screws option a better way to go? What size are the screws? I've seen change from 1/4" to 3/8" but what is the length for the new screws?

TIA, dmh

[mfleming]

Ah, those photos brings back memories (or nightmares if you will) of past repairs. You can press the case halves together without threading the lower screws to check the functionality of the zebra connector and CPU board. Much like bringing a calculator with one broken post back to life by squeezing a lower corner. Best to have the upper screws in place so the upper battery connector provides power.

There was an earlier thread giving details of a lower post repair approach you might find useful

https://www.hpmuseum.org/forum/thread-17264.html

~Mark

[dmh]

I ended up putting it together without any screws and applying pressure top and bottom and it fired up with the good old 'MEMORY LOST' and I was able to run a CATALOG 3 and do a few basic things (with limited spare fingers).

It needed a lot of pressure so I wonder whether the lower post repair and longer screws will be enough to maintain that pressure?!?

The foam behind the battery and module connection looked ok so not sure what else I can do.

The solderless Spice models made me wonder why someone hasn't come up with a similar clip solution to keep the CPU board connected to the keyboard. Pressure on the lower posts wouldn't be an issue then. Maybe there isn't enough room.

[mfleming]

Among the various lower post solutions is one in which the CPU board is directly wired to the base PCB by soldering fine wires between connecting pads. I ruined a perfectly good 41C using this technique, so stay well away from that idea!

[cruff]

I replaced the lower posts on my 41CL conversion with 2-56 threaded standoffs cut to length and reduced to the correct diameter. I used two part epoxy to glue them in place, using the screws and the lower case in place to ensure they ended up in the correct position. It is critical to not touch it for at least 24 hours to ensure the epoxy cures and bonds fully. I think I roughed up the plastic of the top case under where the standoffs attach.

[BillBee]

The replacement Zebras from The Calculator Store are really nice a bonus would be the combination Zebra and lower post repair kit.

-Bill

(07-24-2021 07:28 AM)dmh Wrote:  I ended up putting it together without any screws and applying pressure top and bottom and it fired up with the good old 'MEMORY LOST' and I was able to run a CATALOG 3 and do a few basic things (with limited spare fingers).

It needed a lot of pressure so I wonder whether the lower post repair and longer screws will be enough to maintain that pressure?!?

The foam behind the battery and module connection looked ok so not sure what else I can do.

The solderless Spice models made me wonder why someone hasn't come up with a similar clip solution to keep the CPU board connected to the keyboard. Pressure on the lower posts wouldn't be an issue then. Maybe there isn't enough room.

[dmh]

What are the dimensions of the standoffs?

What is 2-56 referencing?

Thanks!

(07-24-2021 10:45 PM)cruff Wrote:  I replaced the lower posts on my 41CL conversion with 2-56 threaded standoffs cut to length and reduced to the correct diameter. I used two part epoxy to glue them in place, using the screws and the lower case in place to ensure they ended up in the correct position. It is critical to not touch it for at least 24 hours to ensure the epoxy cures and bonds fully. I think I roughed up the plastic of the top case under where the standoffs attach.

[cruff]

2-56 is the size of the (small) screws that thread into the standoff. I apparently didn't make notes about the length and diameter, but the diameter was turned down to allow the standoff I bought to fit through the holes in the 41CL board, and the length to allow the back case to close fully. I turned them down by chucking the standoffs into a drill and using a grinding wheel.