Repairing the back panel of a HP-15c

[sunpazed]

I picked up this HP-15c recently, and am really pleased with it’s condition. However, the back panel is a slightly bent and starting to peel off.

What’s the best approach to repair this?

I’m thinking;

- Use a hot-bag to soften the rear glue.
- Slowly peel off the metal with a spudger.
- Repeat with hot-bag.
- Once off, remove glue with isopropyl alcohol,
- Flatten metal panel by wedging it between flat MDF and weighing it down with a few heavy bricks,
- Clean, and re-adhere somehow.

Any thoughts?

   
   

[Maximilian Hohmann]

Hello!

I wouldn't peel it off. It doesn't really look bad and can only get worse. Your intended method of straightening will probably not work, no matter how many bricks you stack on top of it. If anything, then you may have success by running it through a manual printing press of the kind used by artists to print etchings and wood carvings.
Just put some contact glue under the side that is beginning to come off. And for touching up the type label on the front side I can recommend a "Chrome marker - High Gloss Liquid Chromium" that you can find on places like Aliexpress.

Regards
Max

[vaklaff]

As for flattening, maybe this spoon trick can work? I used it on something but can’t recall the details, probably not calculator related, but it worked. The metal must be quite thin though.

[sunpazed]

Thanks for the feedback.

On closer inspection, it looks like the metal plate is adhered to the body using a double-sided tape that is shaped to the label. By it's age it looks to be original.

This tape is now gunked up in the areas that have lifted off, so I don't think contact glue will work.

Any other ideas?

[BobVA]

You might try cleaning the exposed tape with a little IPA and a non fibrous wipe to see if you get lucky and can "reactivate" the glue. If the label is curled up, though, it's likely to pop loose since the glue will be under stress.

The most reliable approach is to remove the label completely, flatten it and then reapply it. Simple, right? :-)

If you want to have a go at that, there's a lot of past discussions to get you started, such as:here, here, here, here, and here.

Please keep us posted!

[sunpazed]

Those links are great, thanks so much for tracking them down for me!

I'll firstly attempt the IPA clean-up, and failing that I'll carefully peel the panel off and get my rolling pin out (as suggested in the previous posts)

[AndiGer]

Maybe also this will be helpful:
https://www.hpmuseum.org/forum/thread-14...28165.html
Andi

[sunpazed]

Thanks for all your help. Here's how the repair turned out:

   
   

I followed these instructions:

1. Remove the rear cover, and carefully store the screws/springs somewhere.
2. Use a hot-bag to soften the rear glue.
3. Slowly peel off the metal with a plastic spudger. Don't damage either panel.
4. Repeat this a few times with the hot-bag.
5. Expect the rear panel to curl as you peel it off.
6. Once off, remove remaining glue with isopropyl alcohol, which makes a sticky mess.
7. Clean and dry the rear cover.
8. Clean the metal plate. I found that a pencil eraser helped to remove any final stubborn glue through friction.
9. Find a hard flat table with no grooves, and flatten the metal panel with a rolling-pin. This will take a fair bit of time. Using the hot-bag to heat up the metal makes it more malleable.
10. Once perfectly flat, use a good spray adhesive (I used 3M Super 77) to adhere the metal plate to the rear panel. Ensure all edges are covered. Wait for this to dry.
11. Assemble the case, and make sure you don't forget the all important springs.
    

Really happy that my HP-15c now feels normal in my hands without the sharp edges. Thanks again folks!

[rprosperi]

Thanks for posting the resulting recipe, this will help future readers a lot.

Often, folks come here looking for advice and after collecting ideas, go off to make the repair and once done, move on and never bother to comment or document on what worked and how to do it. Yours is a great example of giving back to the community to help the next guy, so as I said: Thanks!

[SammysHP]

Haven't tried it with this specific type of label, but I regularly use dental floss to remove glued batteries and such. Just get a start somewhere and use the dental floss like a cheese slicer.

[sunpazed]

Yep, I had the same idea with the dental floss — it was reasonably effective in this scenario to get the metal plate off.

However, I ended up preferring the plastic spudger as the double-sided tape on the rear panel was fairly brittle. Perhaps it was due to the age, but this tape was very firmly stuck to the plastic.

Either way, I’m happy with the way it turned out, and I hope others can find this info useful.

[vaklaff]

Well done indeed!