HP Forum Archive 12

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HP-42S dead? Message #1 Posted by Mike (Stgt) on 29 Apr 2003, 5:01 p.m. Hello all! I've got a HP-42S today (3305S...) which looks nice but is said to be out of order. Now at home I inserted batteries (which make an HP-21S work - hello Raymond!) but the display stays blank. I did the 'Exit'-'Sqrt' which is described in the manual to test if repair is needed. Nothin than a deep 'Blurp' from the beeper. Not repetable. Now my question: is there a chance to get it back to live? I assumed the contrast would be down to clear display and pressed 'Exit'-'+' several times which led to another 'Blurp', alas since then not the slightest sign of live behind the keys. Is there still hope? TIA.....Mike

Re: HP-42S dead? Message #2 Posted by Ron Ross on 29 Apr 2003, 5:06 p.m., in response to message #1 by Mike (Stgt) Try the standard fix. Short the battery terminals.

Re: HP-42S dead? Message #3 Posted by Mike (Stgt) on 29 Apr 2003, 5:12 p.m., in response to message #2 by Ron Ross Hi Ron! That was a trick for dead HP-41: Bats out for about 7 hrs or even reverse over night. And that still works on HP-42S? Ciao.....Mike

Re: HP-42S dead? Message #4 Posted by christof on 29 Apr 2003, 5:13 p.m., in response to message #2 by Ron Ross I have had on numerous occasions with 17Bii and 42S machines had to short the battery terminals (with a piece of wire). Once I had to do this, put hte batteries in, remove them and do it over again! if that fails, check your cells and try finding a new triplet of silver oxide cells. :)

Re: HP-42S dead? Message #5 Posted by Mike (Stgt) on 29 Apr 2003, 5:24 p.m., in response to message #4 by christof Hi Christof, I did the cycle now 3 times: short the terminal with a paper clip and put the bats back in: Nuthin! And the LR-44 (Made in ... - can't read it) work fine in an other calculator. Ciao.....Mike

Re: HP-42S dead? Message #6 Posted by David Smith on 29 Apr 2003, 5:58 p.m., in response to message #5 by Mike (Stgt) The 42S manual says to briefly short the battery string out WHILE IT IS IN THE CALCULATOR!!!

Re: HP-42S dead? Message #7 Posted by Christof on 29 Apr 2003, 7:38 p.m., in response to message #6 by David Smith short the batteries out while in the calculator? Okay. I need to get home and look at the manual, but that seems pretty odd to do as the batteries make the circuit anyway. I've heard of reversing the batterie sin some calcs but that seems REALLY dangerous and I'd not advise it unless you knew for *sure* that you would not fry the calc. Is the case a bit loose?

Batteries and power on Pioneers Message #8 Posted by Christof on 29 Apr 2003, 9:37 p.m., in response to message #6 by David Smith Having been warned by David of a possible error in my advice I radiply sought out four Pioneer manuals upon returning home- the advice in all four is the same- short the battery contacts out with a coin AFTER removing the batteries. (42S, 20S, 32SII and 17BII manuals) *whew* I was scared my advice was bad for a moment. the various self test keystrokes may be also helpful ?

Re: Batteries and power on Pioneers Message #9 Posted by Ellis Easley on 30 Apr 2003, 1:35 a.m., in response to message #8 by Christof Some manuals - I don't remember whether Voyager or Pioneer - say to short the battery terminals with fresh button cell batteries in place. My theory is that it is an effort to avoid ESD damage by keeping both power supply rails connected by the low impedance of the cells. As your shorting bar approaches the terminals it is a potential source of ESD and without the cells, if the ESD jumped to the Vcc rail first, it might travel through the chips to get to the ground rail which is connected to the ESD shielding, into your hand and back to the earth.

Re: Batteries and power on Pioneers Message #10 Posted by Mike (Stgt) on 30 Apr 2003, 9:22 a.m., in response to message #8 by Christof I did short the bats connectors 2 nite - without the coin cells of cause <VBG> and insertet them this morning: no way to get it working. Display stays clear, no reaction with 'Exit'-'Sqrt'. Ciao.....Mike

Re: HP-42S dead? Message #11 Posted by Mike (Stgt) on 30 Apr 2003, 4:42 a.m., in response to message #6 by David Smith Hi David! Where did you find that advice (page, chapter). Anyway, I'll give it a try. If it brings back the HP-42S it's worth killing the 3 cells. :-) Ciao.....Mike

Re: HP-42S dead? Message #12 Posted by David Smith on 30 Apr 2003, 11:30 a.m., in response to message #11 by Mike (Stgt) I'll check the manual for the exact page. A momentary short (a second or so) will not harm those small button cells. NEVER short nicad batteries... they can produce HUGE amounts of current.

Re: HP-42S dead? Message #13 Posted by Mike (Stgt) on 1 May 2003, 3:18 p.m., in response to message #12 by David Smith Yep, I assume the "inner resistance" of the coin cells is high enaugh for a quick short. I'll tell when it helped. Ciao.....Mike

Re: HP-42S dead? Message #14 Posted by Mike (Stgt) on 5 May 2003, 5:21 a.m., in response to message #13 by Mike (Stgt) Even with the bats in place a short shortage did not help. Seems I have a test object for spare time on rainy days. Thanx again for all advices Ciao.....Mike

Re: HP-42S dead? Message #15 Posted by paul w on 7 May 2003, 2:40 a.m., in response to message #14 by Mike (Stgt) one method that i heard and i used to help fix a workmates hp42 was called "bleeding the capacitor" what i did was take the batteries out then push the on button numerous times (try about 15-20) this is suppose to deplete the capacitor power to nothing which when the new batteries are placed in "reboots" it. hope it works

Re: HP-42S dead? Message #16 Posted by Mike (Stgt) on 7 May 2003, 4:33 a.m., in response to message #15 by paul w I tried that too, may be not often enough. I still have a rest of hope for the HP-42S as two times the beeper made 'burrp'. Ciao.....Mike

Re: HP-42S dead? Message #17 Posted by Paul Brogger on 30 Apr 2003, 11:20 a.m., in response to message #1 by Mike (Stgt) Sounds like your next step may be to disassemble the unit, and swap out the PCB for another (from a 17B/BII, 27S or 42S) to try to isolate PCB problems from keyboard/display/connection issues. It's nice to have a disassembled clean functioning spare -- both keyboard/case/display and PCB -- available for such testing. (I use a 17BII.) Assuming disassembly goes well, the main things to worry about are scratching the PCB traces when you're twisting the hold-downs, and absolutely minimizing the number of times those twisties are cycled. These units were not meant to be serviced, and the metal hold-downs (or whatever they should be called) that fasten the PCB to the display bezel will only stand being twisted back & forth a few times (maybe a half-dozen if you're lucky) before metal fatigue sets in. So don't disassemble/reassemble any more than is necessary. Randy Sloyer has a "test rig" he uses to apply pressure, temporarily holding together cases & PCB's for testing -- that sounds like a good idea. I've tested quickly just pinching things together with thumb & forefinger, but that's got a lot of drawbacks, and may lead to false negatives. If you care to sell the case, I've a working PCB that would LOVE to find a real home . . .

Re: HP-42S dead? Message #18 Posted by Mike (Stgt) on 1 May 2003, 3:16 p.m., in response to message #17 by Paul Brogger When I read yours and Randy's appends I think it's time to hand the HP-42S over to the real experts. But I still hope to be one too (far in the future <G>). Ciao.....Mike

Funny noise in one of the keys. Message #19 Posted by J.C.Serra on 8 May 2003, 10:02 a.m., in response to message #17 by Paul Brogger Hello, I've got a 42s and some days ago i realise that the 4 have a curious noise when it's pressed. The key woks fine but if you put your finger on it without any pressure, only with the weight, it sounds like a 'click'. It seems to be a little space between the spring, if there is any, and the plastic key. If I leave the finger there and press again the key, there is no funny noise. Could somebody explains me how a pioneer key works? Is there any picture? Lots of thanks.

Re: Funny noise in one of the keys. Message #20 Posted by Randy Sloyer on 8 May 2003, 1:21 p.m., in response to message #19 by J.C.Serra I don't have any pictures of Pioneer keyboard internals but can post some if interested. Does the key rock side to side? Try pressing on the left side of a button with the problem. Does the right side rise up? If so, the hinge that stabilizes the key is broken. It cannot be repaired. As you have seen, it still works, it's just not the same as the other keys. The other common problem occurs on newer units made in Indonesia. The keys sometimes click loudly on release. While this is not what you describe, it may be related. What are the first 5 digits of the serial number? From this we can tell where and when the unit was made.

Re: Funny noise in one of the keys. Message #21 Posted by JC Serra on 8 May 2003, 2:52 p.m., in response to message #20 by Randy Sloyer Hello Randy, It is a Singapore unit, 3142S...,and the key is not rocking, when you press on the left the right doesn't rise. I've got a 32sii(ind) and is not the click that the button makes on release. It is a very soft friction sound and it happen even if you touch the key as soft as you can. Thanks for the suggestions. If I see what's inside probably I can speculate with the noise.That's why could be very nice if there's some photos.

Re: HP-42S dead? Message #22 Posted by Randy Sloyer on 30 Apr 2003, 6:47 p.m., in response to message #1 by Mike (Stgt) You'll most likely find the trouble to be one of two things: 1. Fractured solder connections on the 8k ram chip. Happens in about 70% of the dead 42S's I see. Primarily pin 14 - the power supply common pin. Can happen elsewhere as well. If you don't have about 5X magnification, you'll never see it. You can just apply some liquid flux and reflow all connections on the chip, especially near the cpu end. Be sure to clean off all flux residue. 2. The more difficult problem: an electrically stuck key. Since the rows and columns of the keyboard go to the address and data lines of the processor, a stuck key prevents the processor from running. You'll need to remove the logic board to get to the keyboard connector. Check between all 15 connections with an ohm meter - all should read infinity with respect to one another. The only way I've found to clear a short is David Smith's ultrasonic cleaner method of three passes in fresh distilled water each time. Clears about 50% of the shorts. Sometimes the keyboard is beyond cleaning when the conductive material starts flaking off. When that happens it is time for an organ transplant from a good one.

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