HP48SX - shift keys won't stay shifted - preliminary report - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: General Forum (/forum-4.html) +--- Thread: HP48SX - shift keys won't stay shifted - preliminary report (/thread-894.html) |
HP48SX - shift keys won't stay shifted - preliminary report - Bruce Larrabee - 03-13-2014 11:46 AM Okay After dismantling the calculator I can report that this problem is not any of the following; keypad, keypad connection to motherboard or the display. I will keep you folks apprised of anything else I discover. Presumably on the motherboard. RE: HP48SX - shift keys won't stay shifted - preliminary report - W_Max - 03-13-2014 03:29 PM 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. RE: HP48SX - shift keys won't stay shifted - preliminary report - Bruce Larrabee - 03-13-2014 03:33 PM Will make both of those checks. Good suggestion. RE: HP48SX - shift keys won't stay shifted - preliminary report - Han - 03-13-2014 06:31 PM (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. RE: HP48SX - shift keys won't stay shifted - preliminary report - HP67 - 03-13-2014 06:41 PM What about the possibility of bad RAM? Has the OP run all the self-tests? RE: HP48SX - shift keys won't stay shifted - preliminary report - W_Max - 03-13-2014 07:11 PM I very well could be misunderstanding something, but would voltage drops only affect whether a key is detected? I think, the reason is key press itself (some sort of leakage) + activated subroutine (rising CPU current). Other symptom is notable screen contrast cyclic reduce, while key pressed. If power regulator is faulty - drops may be critical for stable CPU functioning, causing "strange" side effects. RE: HP48SX - shift keys won't stay shifted - preliminary report - Bruce Larrabee - 03-14-2014 04:53 AM I will run these checks as soon as possible (am swamped). Code:
|