HP 19C horror show!


Hello all

I knew I was getting an defunct HP 19C but one can only hope. This is a resale of a resale but I needed an example, working or not for the book, so out went the expense and in came the 19C.

Filthy dirty filthy mess! Keys soiled, case soiled and some one attacked the battery compartment with a cattle branding iron instead of a soldering iron!

Melted grooves and plastic in the battery compartment with spare melted solder globs imbedded in the plastic. Both battery contacts loaded with excess solder to a quarter inch in thickness. So much so that I had to remove the excess before extracting the pca from the calculator.

Of course, it took a good hour to get into the calculator due to a rounded philips head screw. Ended up drilling the head off without damaging the screw post or case.

Corrosion was minor, however the print head was imbedded in the smooth platten as it had melted in place!!!

So I disassembled the calculator, cleaned up the pca's. Removed the corrosion (all traces were intact and tested so). All contacts cleaned and SOOT removed from some of the components. Maybe the paper caught fire ;-)

Well as I said, it was for photodocumenting the dissection. Did I mention that two large headed brass screws were missing leaving only one holding the printer in place. Also as tiny screw jack was floating in the wreakage.

Well, desoldering, removing the corrosion and cleaning contacts and etc. have resulted in random LEDS lighting up depending on the off/on cycling of the calculator. It would seem that an attempt was made to repair it by that guy with all thumbs. Probably attached the charger to it with no batteries in it also. The motor works and moves the print to and fro as tested from a 1.5 volt battery attached to the motor leads. Well there are some good parts and the keyboard side looks good so it will display well, or until a working one can be secured.

Does this calc suffer the same demise as the 29C and other woodstocks vis-a-vis, chargers and bad/missing batteries? The new symptoms (at least it lights up ;-) would attest that it does.

some shots of the dismantelling:

(Mike Morrow; this is not yours!!!!!! It is safe and sound and with what I gleam from this will help with yours, hopefully!)

As it arrived, not bad looking:

Back cover a little chewed up with pry marks, not a good sign:

Evidence of a branding iron and bucket of solder:

The contacts, had to desolder prior to removal to get to exit the back of the case:

Keyboard PCA:

LED before and after cleaning soot:

Keyboard trace:

Trace corrosion at base of calculator keyboard pca:

And again after corrosion removed and continuity checked:

And now the printer assembly:

One of three large screws for securing printer assembly to case (the other two are missing). Also a small slotted threaded screw found floating inside, any suggestions?

Melted platten:

Printer PCA, printer and ribbon:

Printer motor and printer power connections:

An overview of the pca's:

Now to clean up the photos, label them and insert them in the text. Still to do with this is a diassembly of the printer system with photos and explanation.

Just one more chapter to photograph then onto the text for three chapters, some appendices and then proofing. Still hoping for a release in San Diego.

Enjoy the photos.


Edited: 9 June 2011, 8:39 p.m.


Great perseverance in a crestfallen venture!

Very nice job done, I enjoy the pictures!


Hi Geoff,

Great pictures. I do look forward to your book (maybe I've said that earlier already? ;-)



Interesting - my HP-19C doesn't have that little swing-out gizmo the right side for a security cable.



They changed that during the production run. I'm not sure whether they added it, or removed it.


Following the logic of the market IMHO they must have removed it. Calculators lost preciousness every year then.


Hello Geoff,

About your question:

One of three large screws for securing printer assembly to case (the other two are missing). Also a small slotted threaded screw found floating inside, any suggestions?

this's a part of a broken screw (one of the two missed screws).




I don't know, Geoff. Maybe it came from HP that way after a bad day in the quality assurance department! :-)


Mike, quality has to be built by production, it can't be "tested in" by QA! :-)


Perhaps Geoff got the rare HP-19C "Carly F." signature model :-)


:-) Nice idea but too early for Carly ... although, hmmmh, you're right: it's her fault in any case ;-)


Hi Geoff,

My 19C doesn't have the security cable tab either.
It's serial no. is 1803S11159, (supposedly built in the 3rd week of 1978).

When was your unit built?

Best regards, Hal


Hello responders and others:

Exschr: thanks for the lament and the kudos!

Walter B: you have!!! and soon (San Deigo).

BobVA and Hal: serial number 1804sxxxxx with the security cradle option.

Ignazio: spot on and thanks, didn't really look at it, but, yes a sheared threaded section of the original brass screw.

And now a before and after on the contacts:

The desoldering and cleaning combined with the work on the keyboard and logic pcas resulted in the following:

Interestingly the display is random and dependent on the cycling of the off/on switch. Also the display of the lit LED's cycles itself, as though the timing logic is still there. This is unlike my HP 21 with the power and logic destroyed by the application of the charger without batteries (a no no). In the 21 the display is locked on one LED and static, does not vary.

Now for the spoof:

E**Y sale:

HP 19C, powers up and displays. Calculator clean with no corrosion evident. Includes rare security cable attachment. Will not perform calculations but probably just needs new batteries. No charger so no way to test it further. Instruction manual not included but is readilly available on the web. Should be an easy fix. Any gullible buyers, contact me at.....

Just to be accurate, it is not forsale, that is a joke, but haven't we seen it before with respect to Woodstocks and others.

Cheers, Geoff

it will make for a nice display when I am done.

Edited: 10 June 2011, 2:43 p.m.


Geoff, if the display "wants" to cycle, this may be a sign of a defective clock oscillator. Look for broken traces or faulty components on the LC1 and LC2 pins of the ACT. Just my $2E-2's worth...



I was thinking along the same lines, but not as technical. I will certainly check as I have not given up yet!

Thanks again!


If the oscillator isn't running, you shouldn't have more than one digit illuminated in the display at a time, unless cathode lines are shorted together, the cathode driver chip is bad, or possibly if the cathode driver chip isn't getting a reset signal. (I'm not sure of how the internal logic of the cathode driver works; if it is a shift register, then without a reset more than one output can be driven.)


Yes, the 19C is just as fragile as all woodstocks to over-voltage damage.

If the clock is not running:

1) LC components bad, traces to same open (rare).
2) Bad VSS/VGG (rare)
3) Bad ACT. (most common failure)

The other common over-voltage damage in addition to the ACT is the combo RAM/ROM (1818-0379).



How have you cleaned the contacts?
And removed the solder?

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