HP-97 Circuit

[hpux735]

(04-15-2021 10:03 AM)teenix Wrote:  I notice in the brouhaha.com HP chips, it has 1858-0044 (quad NPN, anode driver, print head driver, print motor driver) listed equivalent as TPQ3904, but I don't think this can handle up to 500mA for the print heads. 2N3904 would be a discrete transistor equivalent, but current is around 100-200mA. Maybe something like PN2222A or similar (800mA). MMPQ2222A is a quad package but surface mount and different pinout.

cheers

Tony

Hi Tony (and all),

I'm very new here, and have an HP-97 that I inherited from my Wife's grandfather. I've been able to get it basically running, but it has segment `f` lit on all segments on the display. I gather from Tony's excellent notes document that this is due to a failed anode driver IC. I'm guessing by the discussion about replacing the quad transistor IC with discrete transistors implies that an equivalent is unobtanium?

Yesterday, I fixed the printer, and while that works (using the sanding the tires method) the printout is fairly faint. Is that likely from old paper, or should I replace R8?

Thanks!
- Will