HP- 67 1706A04606 - keyboard repaired weird behavior

[albertofenini]

(09-28-2022 12:54 AM)teenix Wrote:  Hi Tony
is this what you call C6 in your HP-67 schematics ?

(09-27-2022 07:30 PM)albertofenini Wrote:  Hi Tony, Hi everyone,

we replaced the 47microF capacitor, which I believe is that connected to Vbsw
old: 50,26microF, Vloss 0,6%, ESR 0,00 Ohm
new: 49,10microF, Vloss 1,0%, ESR 2,3 Ohm

nothing changed in the power-on behavior

then we also replaced the 22microF capacitor, connected to Vss
old: 24,73microF, Vloss 0,7% ESR: 0,00 Ohm
new: 22,44microF, Vloss 0m6%, ESR 0,00 Ohm

again nothing changed in the power-on behavior

We decide to change the two transistors as well :

4-071
old: hfe 331 Vbe 630mV Ic 3,0ma
new : hfe 352 Vibe 641mV Ic 3,2mA

4-668
old: hfe 433 Vbe 645mV Ic 6,2mA
new: hfe 351 Vbe 643mV Ic 3,2mA

after this replacements, the power-on behavior didn't change,
but the reading capabilities increased a lot, almost every card can be read
and also it can now write and read its own written cards

it must be said the the components we used are from an old HP-67 which
also had some issues

where could we get some equivalent new transistors ?

should we also check the six pins Motorola component 3-410 ? (what is this by the way ?)

thanks for any advice, take care !!

Maybe also change the 2.2uF (10-16V) tantalum capacitor near the ACT. The +ve connection is closest to pin 1 of ACT (red dot). This is used for the power up reset pulse for the ACT.

Listed from Jaque Laporte's site...
1854-0071 = 2N3704

1854-0668 = ?? Cannot find any info on it. Maybe 2N3904??

If you check parts suppliers like Digikey and search NPN transistor for the HFE etc that you tested, you may find equivalents.

3-410 is 2 PNP transistors in the same package used for a constant current source for the LED display segments.

cheers

Tony