HP Forum Archive 16

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42S Problem - Switches off straight away. Message #1 Posted by David L. Jones on 20 Nov 2006, 5:32 a.m. Hi I inherited a 42S and it switches off imediately after switching on. In some cases the display will flash for a split second, in other cases it doesn't show anything. If I press the ON key fast enough I can keep the display on until I release the key. The self test (ON-LOG) works just fine, and passes OK. But at the end it just switches off. ON-ROOT (the reset function?) works and very briefly display "Machine Reset" I can even adjust the contrast, and even get it to do calculations if I press a key fast enough at power on, but it switches back off again as before. Anyone know what is wrong? Is there any higher level reset function I can try? The batteries are brand new and tested. Thanks Dave :)

Re: 42S Problem - Switches off straight away. Message #2 Posted by Vieira, Luiz C. (Brazil) on 20 Nov 2006, 6:35 a.m., in response to message #1 by David L. Jones Hi, David; you can reset the entire USER memory contents to its default state by pressing three keys simultaneously: [ON],[Sigma+]and[XEQ]. Yeap, these are the keys at the three corners: left-down, left-up and right-up. With the calculator turned to off, press them all, then release them in the reversed order writen above: release [XEQ], then release [SIGMA+], then release [ON]. A particular message indicating memory loss must appear. This is the 'master reset', although it still depends on software to resume. Leaving the calculator without batteries for some time might cause the best reset ever, but this demands time (some days, maybe). Hope this helps. Success! Luiz (Brazil)

Re: 42S Problem - Switches off straight away. Message #3 Posted by David L. Jones on 20 Nov 2006, 7:25 a.m., in response to message #2 by Vieira, Luiz C. (Brazil) Quote: Hi, David; you can reset the entire USER memory contents to its default state by pressing three keys simultaneously: [ON],[Sigma+]and[XEQ]. Yeap, these are the keys at the three corners: left-down, left-up and right-up. With the calculator turned to off, press them all, then release them in the reversed order writen above: release [XEQ], then release [SIGMA+], then release [ON]. A particular message indicating memory loss must appear. This is the 'master reset', although it still depends on software to resume. Leaving the calculator without batteries for some time might cause the best reset ever, but this demands time (some days, maybe). Hope this helps. Success! Luiz (Brazil) Thanks Luiz I tried that and I got "Memory Clear", but it still keeps turning off! I'll leave the bateries out and see what happens. Any other suggestions? Thanks Dave :)

Re: 42S Problem - Switches off straight away. Message #4 Posted by Chiu Yiu Wai on 20 Nov 2006, 8:08 a.m., in response to message #2 by Vieira, Luiz C. (Brazil) Try to install new fresh battery, maybe the battery low but not low enough announce on display,on my experience low battery always make the calculator unstable.

Re: 42S Problem - Switches off straight away. Message #5 Posted by Bruce Bergman on 20 Nov 2006, 11:22 a.m., in response to message #4 by Chiu Yiu Wai Agreed. My experience with the battery indicator on the 42s is that it doesn't always represent reality. I had a vexing issue with printing to the printer on my 42s, and I thought it might be the batteries, but the indicator was all "nope, you're good!", so I discounted it. After another 20 minutes, I switched them out anyhow and everything printed just fine. So, like the previous poster mentioned, put in some new batteries. thanks, bruce

Re: 42S Problem - Switches off straight away. Message #6 Posted by David L. Jones on 20 Nov 2006, 3:09 p.m., in response to message #5 by Bruce Bergman Quote: Agreed. My experience with the battery indicator on the 42s is that it doesn't always represent reality. I had a vexing issue with printing to the printer on my 42s, and I thought it might be the batteries, but the indicator was all "nope, you're good!", so I discounted it. After another 20 minutes, I switched them out anyhow and everything printed just fine. So, like the previous poster mentioned, put in some new batteries. thanks, bruce No joy, fresh batteries makes no difference. All batteries measure 1.57V Any more ideas? Anyone know how the 42S latches the power on? Is it that small SOT23 package (MOSFET?) I see on the back of the board in the internal photos? Or is it simply low power logic within the ASIC? It's got to be a program thing, as the power latches on fine when doing the self test. Thanks. Dave :)

Re: 42S Problem - Switches off straight away. Message #7 Posted by Karl Schneider on 21 Nov 2006, 11:21 p.m., in response to message #1 by David L. Jones Quote: Hi I inherited a 42S and it switches off imediately after switching on. In some cases the display will flash for a split second, in other cases it doesn't show anything. If I press the ON key fast enough I can keep the display on until I release the key. The bequeathed HP-42S isn't running a program like the following at startup, is it? ;-) LBL 00 SF 11 OFF GTO 00 Flag 11 will run the "pointed-to" program at startup, upon which the flag is cleared -- a feature carried over from the HP-41. Seriously, running the self-test will allow the user to easily escape this "trap" of a program. -- KS

Re: 42S Problem - Switches off straight away. Message #8 Posted by David L. Jones on 22 Nov 2006, 12:58 a.m., in response to message #7 by Karl Schneider Quote: The bequeathed HP-42S isn't running a program like the following at startup, is it? ;-) LBL 00 SF 11 OFF GTO 00 Flag 11 will run the "pointed-to" program at startup, upon which the flag is cleared -- a feature carried over from the HP-41. Seriously, running the self-test will allow the user to easily escape this "trap" of a program. -- KS I have no idea, as it can't switch on (other than self test mode) I cannot check. Surely if there was such a program in there then it would be cleared when the batteries are removed? Dave :)

Re: 42S Problem - Switches off straight away. Message #9 Posted by Vieira, Luiz C. (Brazil) on 22 Nov 2006, 10:58 a.m., in response to message #8 by David L. Jones Hi, David; any user-related data (programs, key assignments, matrices, register data, ALPHA contents, etc.) is erased after a master clear procedure, cofirmed with the 'Memory Clear' message you saw earlier. The small program Karl mentions may actually cause the auto-off behavior you described, because it sets auto-run flag (11) and turns the calculator off. In this case, subsequent attempts to turn the calculator on will cause it to turn itself off straight. I have seen some HP42S with weird behavior, and in some cases I could interfere, resoldering the RAM chip and the other SMD components (two, I guess) solved the problem. Any chance that you'd open yours and try this? If you are not skilled in electronics maintenance, please, do not try it. My 2¢. Luiz (Brazil) Edited: 22 Nov 2006, 11:01 a.m.

Re: 42S Problem - Switches off straight away. Message #10 Posted by David L. Jones on 24 Nov 2006, 3:48 a.m., in response to message #9 by Vieira, Luiz C. (Brazil) Quote: Hi, David; any user-related data (programs, key assignments, matrices, register data, ALPHA contents, etc.) is erased after a master clear procedure, cofirmed with the 'Memory Clear' message you saw earlier. The small program Karl mentions may actually cause the auto-off behavior you described, because it sets auto-run flag (11) and turns the calculator off. In this case, subsequent attempts to turn the calculator on will cause it to turn itself off straight. I have seen some HP42S with weird behavior, and in some cases I could interfere, resoldering the RAM chip and the other SMD components (two, I guess) solved the problem. Any chance that you'd open yours and try this? If you are not skilled in electronics maintenance, please, do not try it. My 2¢. Luiz (Brazil) Thanks Luiz Yes, I have the skills to do that, but I don't fancy spending my time mindlessly resoldering chips hoping it might help :-) Looks like it's a lost cause... Thanks Dave :)

Re: 42S Problem - Switches off straight away. Message #11 Posted by David L. Jones on 25 Nov 2006, 4:12 a.m., in response to message #1 by David L. Jones Quote: Hi I inherited a 42S and it switches off imediately after switching on. In some cases the display will flash for a split second, in other cases it doesn't show anything. If I press the ON key fast enough I can keep the display on until I release the key. The self test (ON-LOG) works just fine, and passes OK. But at the end it just switches off. ON-ROOT (the reset function?) works and very briefly display "Machine Reset" I can even adjust the contrast, and even get it to do calculations if I press a key fast enough at power on, but it switches back off again as before. Anyone know what is wrong? Is there any higher level reset function I can try? The batteries are brand new and tested. Thanks Dave :) Ok, I've managed to get the unit open, and what an effort it was! I drilled out the tabs in the battery compartment and then "snapped" the lower tabs off with the aid of screwdriver, I couldn't do it by hand. Very difficult and touchy procedure. Here is an inside shot: http://alternatezone.com/stuff/HP42SinsideCrop.jpg Anyone notice anything out of the ordinary? I have soldered the metal tabs to the PCB in case they weren't making contact, no difference. I have run the unit from a DC supply in case the batteries internal resistance is shot, no difference. I have replaced the top tantalum cap, no difference. The bottom cap and diode seem to be part of the dot martix display refresh, remove the cap and the display dims, remove the diode and nothing changes. It's not the SRAM connections, because as I said it passes all internal memory self tests. Any ideas? Thanks Dave :)

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