HP Forum Archive 14

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Defect HP-42S Message #1 Posted by Victor Koechli on 7 Jan 2004, 4:02 p.m. Hi all, I have a HP-42S that will just beep rapidly when turned on. Only way to stop it is by removing the batteries. I have tried all kinds of reset, including shorting the battery contacts with the batteries in or out of the calc, all to no avail. My understanding from an earlier thread is that this symptom means the internal RAM chip is dead or has a bad contact. I'm willing to open it and take the occasion to install a 32K RAM in lieu of the standard 8K. My questions are: Is there anything particular that I have to observe when opening the calc? What RAM chips (part#, manufacturer) should I use? Thanks for any help, Victor

Re: Defect HP-42S Message #2 Posted by Raymond Del Tondo on 7 Jan 2004, 4:32 p.m., in response to message #1 by Victor Koechli Hi, have you tried the other thing? Maybe it's just a sticky key contact... Apply slight torsion and pressure (not much of course) to the case, and see (or hear) if something changes. Regards, Raymond

Re: Defect HP-42S Message #3 Posted by Victor Koechli on 8 Jan 2004, 1:22 a.m., in response to message #2 by Raymond Del Tondo You're right, pressing on the back or twisting the case stops it, and the machine works normally - as long as I keep the pressure. What does that mean? Is there a bad contact between the PCB and the keyboard? As far as I can tell, no keys are stuck, and all respond with good electrical contact when pressed. I could easily verify that since the beeping becomes more rapid when a key is pressed. How should I proceed? Thanks, Victor

Re: Defect HP-42S Message #4 Posted by Raymond Del Tondo on 8 Jan 2004, 4:34 a.m., in response to message #3 by Victor Koechli Hello Victor, I once had a similar problem with a 32S. I was on the way opening the unit, and while trying to drill off the stakes in the battery compartment with a screwdriver, I made a pause and tried again to power up the machine, and voila! it worked. My drilling action deformed the stakes just enouth that they applied enough pressure to the pcb to make good contact. AFAIK the weakest piont inside the pioneers is the connection between the 'main' pcb (keyboard) and the display . However, I remember there were threads in this forum which dealt with this topic, but I don't remember when, maybe in the archives... Regards, Raymond

Re: Defect HP-42S Message #5 Posted by gifron on 8 Jan 2004, 9:19 a.m., in response to message #4 by Raymond Del Tondo See the following link for a related discussion. http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv013.cgi?read=46573

Re: Defect HP-42S Message #6 Posted by Victor Koechli on 8 Jan 2004, 5:20 p.m., in response to message #2 by Raymond Del Tondo Thanks everyone for you help, I've solved the problem. It required resoldering the RAM chip, and now everything's fine. The two articles about opening the Pioneers by Paul Brogger were also extremely helpful. What I've done differently is the removal of the lower heat stakes. I've pulled off the metal overlay and drilled out the heat stakes after trying to pry the case halves apart with my fingers. Obviously my fingers aren't as strong as Paul's ;-) Removal of the overlay is actually quite easy, provided you're patient and careful enough. Oh, and I did everything wrong: Used a 500W power drill, no ESD protection, no temperature controlled soldering iron - you get the picture. These little bastards are quite tough! Anyway, I've taken a few hi res pictures, I could mail them or put them up on my website in case anyone is interested. Or if Dave wants them... Thanks again, Victor

Re: Defect HP-42S Message #7 Posted by Randy Sloyer on 8 Jan 2004, 5:27 p.m., in response to message #6 by Victor Koechli I would be most interested in hearing how you removed the overlay without damage.

Removing Pioneer overlay Message #8 Posted by Victor Koechli on 8 Jan 2004, 5:40 p.m., in response to message #7 by Randy Sloyer I was actually quite easy. I started at the top corners, above the display, by lifting them carefully with an xacto knife, then worked my way down both sides of the display. The step in the bezel below the display was a bit of a challenge, it required extreme care and patience. After that, it became easier again. To remove the overlay from the keyboard part I used an old credit card that I slid under it because it is softer and has a large area, and continued downward until the overlay was completely free. Maybe it was easier than expected because the machine is a rather early model, serial # 2910S.... The glue could have aged considerably in the last 15 years. Why are you asking? Is removing the overlay usually destrucitve? Cheers, Victor

Re: Removing Pioneer overlay Message #9 Posted by Randy Sloyer on 8 Jan 2004, 11:00 p.m., in response to message #8 by Victor Koechli Yes, for me, always a disaster. Maybe it was the age of the adhesive on your unit as every time I have tried I've ended up with significant creases and marks. Heating with a hair drier can damage the keyboard, solvents can make a mess of the paint on the bezel, so I open from the back. Some units pop open with no trouble, in general the early USA and Singapore units are easy. Later Indonesian units became very difficult as they overly compressed the lower stakes making for very large mushroom heads that must be pulled through the metal plate. The trick is to hold onto the metal plate so you don't pull it away from the front of the calculator. If you just hold the plastic front in one hand while pulling the back with the other, you can pop the metal over the smaller heat stakes keeping the keyboard layers tight. You usually have no option but to cut off the offending small mushroom so the keyboard plate becomes flat again. Learned that the hard way. Glad your effort was a sucess.

Re: Defect HP-42S Message #10 Posted by Veli-Pekka Nousiainen on 9 Jan 2004, 5:37 a.m., in response to message #6 by Victor Koechli Pics?

Re: Defect HP-42S Message #11 Posted by Erik Ehrling (Sweden) on 9 Jan 2004, 12:07 p.m., in response to message #10 by Veli-Pekka Nousiainen Of course we want the pics! Another idea comes to mind - if the positions of the lower heatstakes are known wouldn't it be possible to drill them out from the backside. Of course you would get ugly holes on the backside that you need to cover in some way, but at least you wouldn't risk bending the keyboard too much... Best regards, Erik

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