|Re: HP-67 repair display|
Message #2 Posted by Tony Duell (UK) on 23 Sept 2001, 1:49 p.m.,
in response to message #1 by Bob Heimbueger
Numbering the pins on the displays as on a normal DIL IC package, with pin 1 on the top right, the pinout seems to be :
1: Ag, 2: k2, 3: Af, 4: N/C, 5: Ab, 6: k4, 7: Aa, 8: k5, 9: Ae, 10: Ac, 11: k3, 12: Ah, 13: Ad, 14: k1.
These are common cathode displays (one cathode line for each digit, and a segment anode line for each segment (which I've named conventionally, h being the decimal point). Since you are missing a segment (rather than a digit), it would appear that you have an anode driver problem.
7 of the 8 anodes (all but 'g' -- the middle horizontal bar) are driven from the 16 pin chip on the keyboard/display PCB. It's normally house-coded 1858-0050, and is actually an RCA CA3082 transsitor arrayu (not custom HP :-)). The g segment is driven by discrete transistors on the PCB, so check those if that's the missing segment. The inputs to the anode drivers come over 8 of the pins from the logic PCB (start at thr fifth pin counting from the R/S key side of the machine). Check for bad contacts here. On the logic PCB they're driven by the 18 pin ROM0 chip (1818-0268), which is, of course, HP custom.
That should get you started....