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Jonas Sandstedt · 02-10-2023, 10:23 AM

Hello,
I have just acquired an HP-19C that seems to work fine, there were very little battery leakage residues that were easily removed. The printing is, however, somewhat uneven as shown in one picture. In the middle of each digit the printing is faint, but not always. I have measured the printhead resistances and they seem OK, and I have removed the printhead flex cable and inserted it again. The resiliently arranged plate behind the printhead is somewhat uneven due to wear, I do not know if that may have any significance. If anyone has any suggestion regarding a cause and possible remedy for this, I am of course grateful.
Another question regards the front label that has peeled off as shown, and it is difficult to get it smoothly back again. The more old glue residue I remove, the more the label gets deformed. I think the best way is to remove the label completely, remove all glue residue, try to straighten the label and re-mount it again. Does that seem to be a good strategy?
Best regards Jonas

teenix · (This post was last modified: 02-10-2023 11:59 AM by teenix.)

If the print head resistors seem ok and the printer platen seems flat and smooth and still spring loaded, then the weak link in the printer head circuit is probably the top row connectors between the CPU board and the lower C shaped board. I'd check these for corrosion. It seems like only one connection would be faulty.

Otherwise, it may be the chip for that drives that particular segment may be going faulty.

Myself, I would warm the label with a hair dryer and carefully remove it. Then clean off any remaining glue, straighten and reattach it. Not sure what is the best glue to use though. Contact adhesive ?

cheers

Tony

Jonas Sandstedt · 02-10-2023, 01:46 PM

Thanks for the suggestions, Tony.
I will take a look in the weekend, and hopefully make some progress.
Best regards
Jonas

Jonas Sandstedt · 02-17-2023, 10:23 AM

Hello,

It was fairly easy to remove the label and remove the glue, a little more difficult to get it really smooth. Now it is back in place with the help of some double-adhesive mounting tape.

With a new battery in my DMM and better glasses I could determine that all printheads have about 12 ohms resistance except the two with the "dim" print, they have about 16 and 18.5 ohms, respectively. I guess that means that the problem lies in the printhead.

Best regards
Jonas