HP-19C Repair Odysee

[PANAMATIK]

(05-09-2021 12:25 AM)[kby] Wrote:  There should be a pot that adjusts this. There is on the HP-10.

This would be too easy. The 50k poti P2 is adjusted to about 10k, I measured it, turning it doesn't change anything. Also I have replaced the U11 LM339 comparator IC, but this was not successful too. It could be a defective Network U17 or the PIK chip itself, which regulates the motor speed.



The keyboard of my "totally corroded HP-19C" was not too bad allover, but some keys were stuck. Therefore I cut a trapezoidal opening into the clear tape to get access to the contacts under the dome. Cleaning with a soft cotton swab with diluted alcohol made the keys work again.



There is also a trick to simplify combining the two PCB boards when assembling the HP-19C, which is said to be very difficult. Remove the LED display, then first stick the horizontal contacts by looking through the hole to the left, for getting their actual position, then moving the short distance to the holes. The following step is, also stick the vertical pin contacts, which is now rather easy.





Bernhard