HP-19C Repair Odysee

[teenix]

(03-08-2021 10:47 AM)PANAMATIK Wrote:  The HP-19C printer module is more suited for development than HP-97, because its mechanic cannot get blocked. Also I would take my partially damaged printhead, which has still 2 pixel lines left for developing. I see two different ways to go:

1.) Development of a new HP-19C processor board with integrated keyboard scan and printer pixel output in one chip, could be a PIC processor. This would spare the complicated communication through ISA and DATA line between ACT and PIK. This solution is not suited for HP-97
2.) Replacement of the PIK chip as exact as possible, suitable for HP-19C and HP-97. I assume it would need a FPGA solution for correct timing and it is more difficult to develop (not to mention alle the level shifting problems).

I'm not sure which way to go at the moment.

Bernhard

The 19C certainly seems a better option for printer interfacing. I can leave the heads disconnected for most testing. I might have to add a temporary switch to detect the print carriage far left movement to open circuit the motor as a safe guard. It would have been nice if HP designed the 97 carriage screw setup the same as the 19C but perhaps was too late to change the design.

I don't think FPGA is required, I already have working PIC code for the 97 which I know prints correctly formatted data while performing the other required functions. I am sure it could be easily ported to a PIK chip scenario even with the bus interface requirements. The downside is risking damage to the CPU board which you will be familiar with from developing your other great products.

I also have two thoughts with the 97 CPU board. I can go with interfacing to the original printer board, or add new motor and head drivers. The original printer board seems quite dependable and is made of available parts, (although fixing the encapsulated PWM module innards would be tricky). I have a motor driver chip suitable for battery systems and am going with that at the moment as this gives a solderless changeover, but both methods have their ups and downs, a bit like my job as a pilot ;-)

cheers

Tony