Woodstock HP-27 ACT woes...

[teenix]

(09-26-2016 06:41 PM)jupiters_spot Wrote:  I'm curious how one goes about determining that the ACT is the root of the problem. I have exactly one HP-27 that's intermittent, so it's hard for me to measure known-good values and compare to my problematic calculator.

I do have a couple of HP-21 calculators, but from discussions on Panamatik.de it seems the CMOS technology differs on the 27, so again, not a good "apples-to-apples" comparison.

A stab in the dark but...

Semiconductors will surely break down over time and it is possible that a single bit (ie transistor) in the thousands that make up the ROM, ACT or other chip circuitry works "mostly" and due to temperature and possibly other effects, that rogue bit may fail to operate properly causing intermittent behaviour.

Could even be a bad discrete component like a capacitor or old carbon resistor that is part of the circuitry, they too can begin to fail over time.

Some "gunk" that's managed to get on the circuit board from a cup of coffee that was spilt ten years ago. Over the years of handling and vibration, an old solder connection on a component has become a partial dry joint.

Very hard to fix a problem like this without having specialised test gear or some plug in replacements to find the culprit. A CRO probably won't pick up internal chip faults.

An hour in the fridge or a brief time under a hair dryer might expose a temperature problem, but maybe unwise to stress out aging (perhaps irreplaceable) components further.

My old HP-45 played up about a year after purchase and I would never have thought to try and fix back in those days. HP did though, and it looked brand new when they returned it.

cheers

Tony