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hoshikawa · 04-05-2014, 03:09 AM

Hello all,
I have a very nice 19C with a very dead printer. The symptoms are blank display and no motor activity on print command. I have read that running a 19C from the wall charger with no battery will kill the printer every time. My question is what should I be looking at repair wise? Or is it hopeless?
Kind Regards,

**Katie Wasserman** · (This post was last modified: 04-05-2014 05:03 AM by Katie Wasserman.)

I wouldn't say

Quote: that running a 19C from the wall charger with no battery will kill the printer every time

but it's not good practice to do so.

The printer needs a lot of current to run, have you tried running the calculator from known good nicad or nimh batteries (or an external DC power supply capable of delivering at least 2 Amps)? Also make sure the battery contacts on the PCB are very clean.

If that doesn't help, open up the machine -- not hard to open but hard not easy to reassemble -- and look for corrosion on the power supply PCB or the main PCB. If all that's good then get a copy of Tony Duell's hand drawn schematic of the HP-19C and check out the motor driving circuit: it's a comparator driving a few transistors.

hoshikawa · 04-05-2014, 12:09 PM

Thanks for the reply!
I am currently running on a modified battery pack with alkaline cells, the problem existed with NICD's as well. I have opened it up but it was pretty clean inside. I am not familiar with the schematics you referred to.
Regards,

hoshikawa · 04-06-2014, 02:45 PM

Hello all,
Upon investigating the circuit (without any schematics) I came across a few motorola transistors in what I think is the motor drive area of the PCB. I cannot seem to find a cross reference for these transistors. they are 3-393 and 4-071 which I took to mean 1853-0393 and 1854-0071 but I have no way to know if this is correct.
regards,

Raymond Del Tondo · 04-06-2014, 03:02 PM

(04-05-2014 12:09 PM)hoshikawa Wrote: I have opened it up but it was pretty clean inside.

Looking at the pics of your next post, I can assure you that it isn't "pretty clean inside", but rather corroded. There are battery acid remains (the green stuff) all over the pcb and on the electronic elements. There's a big chance for the corrosion beeing the cause for the malfunction;-)

hoshikawa · 04-06-2014, 03:17 PM

(04-06-2014 03:02 PM)Raymond Del Tondo Wrote:
(04-05-2014 12:09 PM)hoshikawa Wrote: I have opened it up but it was pretty clean inside.
Looking at the pics of your next post, I can assure you that it isn't "pretty clean inside", but rather corroded. There are battery acid remains (the green stuff) all over the pcb and on the electronic elements. There's a big chance for the corrosion beeing the cause for the malfunction;-)

so you cannot help me to cross reference then?

hoshikawa · 04-06-2014, 03:32 PM

I am making some progress, this transistor is open base to emitter. now to find a suitable replacement.

**Katie Wasserman** · 04-06-2014, 05:00 PM

(04-06-2014 03:32 PM)hoshikawa Wrote: I am making some progress, this transistor is open base to emitter. now to find a suitable replacement.

The 3-393 is likely an abbreviation of an HP part number. Here's an old thread discussing this. There's some conflicting info in this thread, the suggested 2N3330 might not be the correct replacement; Tony suggests that it's a Silicon PNP but a 2N3330 is JFET.

hoshikawa · (This post was last modified: 04-06-2014 05:15 PM by hoshikawa.)

Success! it was a long shot but I substituted a 2n2907 PNP and it worked! The emitter is connected directly to Vcc so that might explain the failure. Many thanks to Katie W.

**Katie Wasserman** · 04-07-2014, 12:29 AM

Always happy to help get an old calculator working again!

Although I use the 32Sii and 12c most often, I think of the 19C as my favorite HP calculator of all time. It looks incredibly cool and had a decent programming model for back in the day. But most of all it was/is the only handheld LED programmable with a printer (at least the only one I know of).

hoshikawa · 04-07-2014, 01:12 AM

(04-07-2014 12:29 AM)Katie Wasserman Wrote: Always happy to help get an old calculator working again!

Although I use the 32Sii and 12c most often, I think of the 19C as my favorite HP calculator of all time. It looks incredibly cool and had a decent programming model for back in the day. But most of all it was/is the only handheld LED programmable with a printer (at least the only one I know of).

I see you even have the 19C decimal as your avatar! I agree it is definitely the most awesome in my collection and a true testament to it's design that a novice like myself was able to fix it.