HP-19C Printer

[teenix]

Hi all,

I see that the 19C circuitry has components for reversing the printer motor whereas the HP-10 does not. Without reverse, the HP-10 would have to let the print carriage traverse the full width before returning to the home position. Both the HP-10 and HP-19C printer drive mechanisms will automatically reverse the carriage when it reaches full width, so I can't see why reverse for the 19C is needed except to speed up printing for short lines.

I don't have a working 19C, so I was wondering if someone that does can help out.

I am trying to determine if the printer always prints a full width line even though something like "0.00" is printed. For example, does it print the partial line then reverse like the Topcats do or does the carriage travel the full printer width then home itself.

cheers

Tony

[Thomas Okken]

The HP-19C printer always prints a full-width line. I don't have an actual HP-19C, but I used to, back in the day, and you can find a few videos of the 19C printer in action by searching YouTube for hp-19c printer.

I'm pretty sure it also moves the print head all the way for SPC (paper advance), but I can't get confirmation of that in the aforementioned videos, and my HP-19C days were far too long ago to trust my memory on such a detail.

[tangdfx]

Hello,Tony

I just confirmed with my 5 HP19s.

The print head will go through full stroke.

The HP19 doesn’t need to reverse motor. It is the mechanism to let the print head come back to original position.

The print assembly could exchange between HP 10 and HP19C.

[teenix]

Thanks guys, much appreciated.

I wonder why the extra circuitry for motor reversal. I suppose it could be used for line feeds using [g][SPC], but this seems a bit silly.

cheers

Tony

[brouhaha]

(07-02-2024 11:53 AM)teenix Wrote:  I wonder why the extra circuitry for motor reversal.

Possibly just that it's derived from the printer circuitry of the Topcat models, and that the 19C electronics was finalized before they decided that its ROMs would only print full lines.

[teenix]

I get it now after looking a bit closer at the schematic.

Even though the signal from the PIK chip comes from the REV pin, it is not actually reverse. The circuitry bogs down the sensing of the motor back emf thus fooling the PIK chip that the motor is too slow. The PIK responds by making the motor go as fast as possible. It does this after finishing printing all characters and the print head should then get back home pronto.

Thanks for the answers

cheers

Tony

[brouhaha]

Cool! Great job figuring out what it's doing!