HP48SX - shift keys won't stay shifted - preliminary report

[Han]

(03-13-2014 03:29 PM)W_Max Wrote:  Hmmm... Can you simulate keypresses without keyboard connected (manually short ribbon contact pads)? I'm still sure, that the problem is hardware related. Another guess - faulty power controller - I discover significant voltage drops on some machines, while you press some keys.

I very well could be misunderstanding something, but would voltage drops only affect whether a key is detected? It seems the issue is not that the calculator never detects a key. It was already stated (in a different thread) that the key presses actually produced the relevant annunciators -- but that it only remained active very briefly.

Is it possible to press (and hold) a shift key to keep the annunciator on? And if so, would it then be possible to do a shifted action by press-and-hold-shift while then pressing a secondary key? I ask because the key handler in the ROM behaves in a specific way. When a key press is detected, it gets saved in a key buffer (including the shifted state). The detection process compares a old keyboard state (i.e. the state of all keys) with the current keyboard state to detect what had changed, and converts this to a key code. The fact that the annunciator turns on and then off suggests to me that something is causing a "secondary" key press (even if you physically only press the key once).

I do agree that the problem is likely hardware related.