Hello out there,
my 25 shows -when switched on- only one or two zeros.
The position manipulate herself when I switch it on a second time.
Any with an idea ?
My 21 has a bad LED at position eight - I cleaned the contacts without an result. Couldt this be a chip failure?
Regards
Around 85 percent of similar failures seem to be caused by a defective ACT chip (the 22 pin, 0.4 inch wide chip). Most likely the bad digit in the LED is a bad LED display module (80%) or a bad cathode driver chip (20%).
Are such chips available today, aside from scavenging from another calculator?
Nope, like 99% of all chips in HP calculators the only way to get them is to salvage another machine.
Thank you for information.
I changed the LED - same result, the 8th digit dosn´t
light up on my 21.
best regards
If you want an HP25 that works and are willing to gamble your HP21, then you can remove the HP21 ACT chip and use it in the HP25... something not recommended unless you (or somebody you know) are quite skilled at desoldering and soldering.