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HP Forum Archive 20

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HP 19C continuing!!!
Message #1 Posted by Geoff Quickfall on 27 July 2011, 8:05 p.m.

One simple question.

I spent an hour working on this calculator mechanically removing the cemented blue corrosion. I used a dental pick and fiberglass brush. Ethanol and a natural bristled paint brush to rinse with.

What can I soak this in to dissolve the blue corrosion.

Now to the calculator. I purchased this one for parts for the ACT chip and swap to the 19C from this post:

The other 19C

The calculator was missing the LED red plastic lens and the calc was described as non-working, with original battery pack. So I had no illusions that it would function. Wasn't cheap (100USd) but I can justify as it is for the book.

Here is a top view with the missing lens:

For the heck of it, I removed the battery pack (not bad) and cleaned the minor dusting of white powder off the contacts. Then attached an alternate battery pack with clips to the appropriate contacts.

It not only lit up but PRX printed the display. All 98 program registers and functions were perfect!! So now the "Other calculator" is to be the donor.

Started to disassemble and was met by this internal label:

Investigating further; HOLY COW look at the before pictures and you tell me if it should have lit up!!!!

Even the two capacitors at the battery contact PCA were delaminated and rotting. I actually thought there were three caps on this board:

So time to clean up.

On these two photos most of the contaminant was removed and unfortunately a trace was missing a section after cleaning. Corroded through for a 1cm section. This was bridged by a black wire seen below.

I used the donor with two good caps to replace the two bad caps (but functioning):

So now here it is with the donor lens in place and back to the first question. What does one use to dissolve the blue (vinegar bath?).

Cheers, Geoff

THE CL is AWESOME! it is the only calculator I use now! Unsolicited advertising for the CL.

Edited: 27 July 2011, 8:06 p.m.

Re: HP 19C continuing!!!
Message #2 Posted by aj04062 on 27 July 2011, 8:41 p.m.,
in response to message #1 by Geoff Quickfall

Hoochie Mamma, that's a wicked lot of corrosion.

I've used vinegar baths. I usually warm it up in the microwave so the acid can really be active. It's fun watching the chemistry experiment in action.

I usually place it under the vent in my kitchen as I have no idea what gaseous byproducts are being emitted.


Edited: 27 July 2011, 8:42 p.m.

Re: HP 19C continuing!!!
Message #3 Posted by Bart (UK) on 28 July 2011, 4:54 a.m.,
in response to message #1 by Geoff Quickfall

Hi Geoff,

Here is some advice our good friend Luiz gave me some time ago (he refers to pictures that are unfortunately no longer available):

"The TI59 board (right side) has a lot of oxidation, and the TI58C board (left) seems cleaner, right? They had both about the same oxidation level before I left the TI58C resting for about 20 hours in a solution of 30 to 40% alcohol vinegar with hot water (could touch it without feeling pain...). You can see some of the copper oxide in the TI58Cīs PC100A contacts, and also notice the missing copper (parts totally destroyed).

Battery leakage is mainly basic (PH), and the alcohol vinegar is acid, so they react with each other and the remains of the reaction (a salt, right?) is easily removed with a paint brush, current water and neutral detergent. As you can see, I removed the LED display, power supply and some components (transistors, elect. caps, "SSS" module contacts, etc.) prior to clean it up.

I have been doing this for some time (woodstocks and these TI's, mostly) and have successfully removed copper oxide from them. In one particular case, a TI59 board with extensive oxidation damage, had the remains of many copper tracks being dissolved or popped out of the mainboard.

The hot water accelerates the reaction, but after some time its temperature raises down and the reaction decelerates as well. Anyway, I always keep my eyes over the board during the process and never let it stays for more than 20-22 hours."

Hope this helps

Re: HP 19C continuing!!!
Message #4 Posted by Mark Henderson on 28 July 2011, 3:08 p.m.,
in response to message #3 by Bart (UK)

Yesterday I worked on a non-working 29C purchased in January from TAS. Upon opening it had the (expected) corrosion, not as severe as the 19C here, but clearly enough to cause problems. Soaked for only a few minutes in warm water with white vinegar and a drop of dish washing liquid, brushed with a nylon brush, air-blast dried. Some cleaning of the case and keys, reassemble - and it WORKS! Perfectly!! So happy! I also have a working 19C and love the calc (especially that the X-register is preserved through power-off, unlike all the other LED "C" models). So today all my work is being done on my almost-as-new-looking 29C!!!

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