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Full Version: Restoring Classics: 409 removed some lettering!
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I'm a long-time HP calcaholic and just getting started now buying and restoring Classic series calcs. Befroe starting my first project (a pretty sad HP-55) I read up everything on this site and elsewhere. I was able to get the dead 55 running in just a few minutes (a broken trace - I am an EE so this is my area of expertise), much to my delight. The keyboard and display work perfectly, so "all" that was left was the cosmetic restoration. In the mean time I'm using it as my daily calc and LOVING it.

After complete disassembly I prepared to wash the case halves in a diluted 409 solution. After soaking in the solution for just a few minutes, I pulled out the case top and to my HORROR several of the pad-printed legends (gold/blue) were dissolving away!!! I've not read this anywhere? Previously the letters were in GOOD shape. not all of them dissolved, but now it looks really shabby :-( My long term intent is to create a new overlay (if successful I will post here).

Has anyone else seen this problem? I'm getting 3-4 other Classics ready for restoration, but I'm really nervous about this step.



Just now collecting or just now getting to the classics? I'm sure you've read about the "dangers" of being "bit" by this "bug".....

How horrible about the lettering! I've never tried 409... and won't ever, now.

I've had great luck with just dishwashing liquid and gentle rubbing under water with my fingers. Afterwards, I polish with Armor-All car vinyl spray... a very light coat, wiped nearly completely off with a clean rag. Restores the shine and, actually, when rubbed hard, removes grime and restores the finish. I've never seen the painted letters removed with this.

I've had no luck trying to restore the letters :( An overlay would be fantastic. I've replaced some model number face-plates with scans printed onto self-sticking paper. You might be able to replace the lettering in this manner, though it will never be perfect....

You know what this means... you have to find another HP-55, one for show, and one to use.

Happy Programming,

Mark, if CDs can be printed on by ink jet printers, why not the faceplate of your calc (or a replacement?)

Actually, and unfortunately that you have not seen it, it has been mentioned.

first the nevers:

-  Never, never use a harsh cleaner, (409, Fantastic, etc).
- Never rub the or brush the silk screening.
- Never use an abrasive.

secondly the how too:

-  use an extremely dilute soap solution.  A drop or two of dish
detergent in a gallon of luke warm water.
- if a brush is required let soak and use an artists brush or
makeup brush (wifes with permission)
- dab the area to be cleaned, never brush it
- rinse
- when drying, dab the area, do not rub or
- let airdry
- mask off the keyboard and apply a matte laqueur finish.

the why it happens:

-  solvents in the air (lab environment, alchohol based etc) and
UV light slowly destroy the in house fixing agent used on the
- although the silkscreening looks good, it is extremely
- Using the matte spray will consolidate the silkscreen material.
- the matte spray is optional

Many restorers here have used armoral (vinyl and plastic reconditioner, but I do not as I don't know the long term affect it will have. Also it does nothing to stabilize the silk screen from futher decomposition under UV. Of course if you have cleaned it and are not using it except for display then the matte spray is not required.

It is interesting to note that even my HP-55 was faded looking after treating its keyboard with kid gloves. The following have all been restored and stabilized with matte laqueur.

The Woodstocks are notorious for faded and washed out silkscreening!

Cheers, Geoff

Here is an overlay for the HP-41CX done on clear sticky backed lable film and run through the inkjet. Also works with Laser printer:


Edited: 10 Dec 2009, 5:34 p.m.


My restorations are pretty, but not that pretty!!! Nice job! I especially like the furry model in the last photo... must have been a prototype.

I think there's a spot on that HP-55 that you missed... you'll have to do the whole thing over again. Just kidding.

Thanks for the great information and photos. I've been reluctant to spray the keyboards, not trusting my own skill with such a permanant sealant. It looks like a superior method, though, from your photos...



Cute dog!

I've been using Novus #1 for cleaning old calculators for years and never had a problem. Before I learned my lesson I used to use isopropyl alcohol and while it's great and removing ink marks it can and will take off the paint on old HP calculators.


Before I learned my lesson I used to use isopropyl alcohol and while it's great and removing ink marks it can and will take off the paint on old HP calculators.

This is a lesson that I learned earlier this year as well - took the print right off the "Alpha" key on an old Casio (fx-4000p). Fortunately, I "got away with" using it on the HP's that I had already cleaned with it.


Geoff (and others) -

Thanks for the detailed response and incredible restoration photos - gives me great hope and inspiration!

In the post-mortem I came to the conclusion you stated - some of the keyboard areas appear to have been exposed to different contaminants (e.g. top row, lots of finger-borne contaminants) which have weakened the printing in various ways. Some of the legends were completely unaffected, some were almost removed... I will be much more careful in future... I do see that some of your 55 legends are faded, mine look very similar now, too.

I may just spray it and live with the "faded" look, however I've had some early success in creating an overlay artwork that looks much better than I expected, so next experiment will be to see if I can use inkjet dry transfer materials to put this artwork onto plastic.. If it works I can see creating artworks for all the Classics as required...

Meanwhile I've accumulated a few 45s and 80s to also restore - this is fun!



Too much fun.


As usual, beautiful restorations!

However, for the restoration of the dog, I thing the eyes are missing...or maybe LEDs :-)



However, for the restoration of the dog, I thing the eyes are missing...or maybe LEDs

I think his dog navigates by radar ;)

Whats all the fuss, who needs eyes?

I use this!

Thanks for the comments on the restorations!

cheers, Geoff

This dog has a radar nose.