The Museum of HP Calculators

HP Forum Archive 05

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Dead HP-27S
Message #1 Posted by J. Lopez on 29 Mar 2001, 2:47 p.m.

I just landed a new old-stock HP-27S. The calculator seems to have been stored in a shop window forever and it didn't come with any manuals or case.

When I installed three new LR44 batteries, the display showed a "MEMORY LOST" message in very dim characters. Trying to adjust the contrast with [CLR] + [+] does not help and the it seems to change intermittently in intensity. Some keys are not responsive. The calculator looks good cosmetically.

I took the batteries out and plan to leave them out for awhile to see if this has any effect in the calculator.

My question is, is this machine dead or is there anything I should do before throwing it into a trash bin?

I'd appreciate any feedback.

Re: Dead HP-27S
Message #2 Posted by Andreas Stockburger on 30 Mar 2001, 6:20 a.m.,
in response to message #1 by J. Lopez


" When I installed three new LR44 batteries, the display showed a "MEMORY LOST" message in very dim characters. Trying to adjust the contrast with [CLR] + [+] does not help and the it seems to change intermittently in intensity. Some keys are not responsive."

Did you check the battery-contacts ?

What do you mean with "Some keys are not responsive" ? Are you able to calculate something ? Could you select Menues ?

Best regards

Andreas Stockburger

Re: Dead HP-27S
Message #3 Posted by Paul Brogger on 30 Mar 2001, 8:05 a.m.,
in response to message #1 by J. Lopez

How many different sets of "new" batteries have you tried?

Re: Dead HP-27S
Message #4 Posted by J. Lopez on 30 Mar 2001, 9:47 a.m.,
in response to message #3 by Paul Brogger


Yes, I checked the battery contacts. As a matter of fact, the calculator does turn on when new batteries are installed, but some keys (mostly those on the right two columns) don't do anything when pressed.

I've been reading in the museum some old documents describing similar problems with other HP calculators, and found that, as some knowledgeable people here suggest, twisting the calculator somehow makes the keys work. I've been able to bring up the TIME menu (the TIME menu key is in the right-most column of the keyboard) and have even entered the current date and time (nice feature in a Pioneer-type calc. I can't stop drooling just thinking about this feature in my HP-42S). The calculator has kept the time correctly for about 12 hours now.

The calculator looks fine and, if I manage to have it take my keystrokes, it returns correct, logical results.

I've tried leaving it without batteries for a few hours and, amazingly, after I put the batteries again, I still had the contents of register 1 unchanged, but some keys are still not working. The manual suggests using a coin to short-circuit the battery contacts for a few seconds. No use there either.

Oh, I've tried two different sets of new batteries (in the shop where I bought it, they put in a brand new set as I was there, to show me it worked --which it didn't and, thus, I was able to buy it for a pittance).

Anyway, I must say I'm encouraged by having the calculator come on and perform some calculations correctly. The only problems I see now are the keyboard and the screen contrast, which is too dim (this might not be a different problem itself, as I haven't been able to make the key combination [CLR] + [+] work, being that the [+] key is not working.

Sorry for the long post, guys. I sincerely appreciate all the help. It's a pity to have such a nice piece of calculator not working. I think I might even learn to like this non-RPN machine... it's just too bad it's not programmable.


Re: Dead HP-27S
Message #5 Posted by Ron Ross on 30 Mar 2001, 11:01 a.m.,
in response to message #4 by J. Lopez

Oh, but it is! That is if you can call Hp solve programming? I do, since you can make any algebraic equation into a function to solve, therefore you now have a new function available. The very reasons you mention are why I feel this is Hp's 2nd best calc made, even though it is algebraic. My favorite is the 42, but I envy the clock and solver of the 27 (though I like the menu system of the 42 better also).

Re: Dead HP-27S
Message #6 Posted by Paul Brogger on 31 Mar 2001, 10:08 a.m.,
in response to message #4 by J. Lopez

Maybe you're drooling on the calculator too often. ;o)

Actually, inside, the printed circuit board (PCB) has two rows of gold contacts which are lined up with matching contacts on the other two internal subassemblies: the keyboard and the display. (Look at the last two of three "internal" pictures under the HP-42S section of the MoHPC -- you'll see the keyboard and (barely) the display contacts in the second of the three; and the contact side of the PCB in the third.)

Electrical contact is established by the PCB being held in place so the rows line up. and by mechanical pressure applied by the aluminum "twist" hold-downs which bind the PCB to the front of the calculator. I suspect that oxydation or some other contaminant has separated some of the keyboard contacts, or that some of the foil traces on the keyboard's mylar circuit sheet have been damaged. (The PCB is probably not very loose, but that might have happened.)

It IS possible to take these things apart, clean the contacts, and put 'em back together. The only REALLY dicey operation I've encountered in Pioneer repair is removing the LCD from the front case, and you wouldn't need to do that.

I suggest you find a model you don't mind experimenting with -- maybe a 20S or 14B or some such. Take it apart as detailed in my "Pioneer Observational Internals" article elsewhere in the MoHPC. (Feel freel to contact me with any questions.) After you've got the feel of it, I'm confident that your 27S may be fixed.

A simple cleaning should do, but if you need to replace the keyboard mylar sheet, that's a more involved operation, but not necessarily more risky.

Re: Dead HP-27S
Message #7 Posted by J. Lopez on 1 Apr 2001, 10:56 p.m.,
in response to message #6 by Paul Brogger

Drooling too much, huh? Yeah, maybe the salinity in all that saliva raining on the poor calculator could concentrate to a point where the electrical contacts between the PCB and the keyboard are obstructed. However, this does not explain why the problem happens only with the keys of the right side of the calculator. I try to keep my calculator squarely symmetric under my face when I'm punching in keys, so my drooling should fall straight in the middle of the keyboard. Hmmm. Nope, I don't think that's the cause.

Anyway, another friend (who doesn't know much about calculators) suggested that I take the batteries out and leave them out for about a week, keeping myself as far away from it as humanly possible during the time. After this, I should install the batteries again and approach the calc with a different attitude, punching its keys softly until they produce an effect. He says it's all a matter of knowing how to push its buttons and that the time and distance I'm putting between us now will wipe out any bad memories kept alive by persistent capacitor agents of any traumatic mishandling of my part in the past. The calc is not completely unresponsive (the keys on the left side do work and she gets turned on when I push the lowest left-side button). He says maybe she likes rough handling as I've confessed to him that I twist her in all directions to get some response. Some individuals stop responding to their usual stimuly of excitement and require different motivation at some point, according to him. Further, he says that, if this doesn't work, he would consider giving us professional advice in his office, for a charge. Oh, he's a psychologist specialized in counseling broken marriages.

Seriously now.

I don't wanna give up my 27S for dead just yet. I've read Mr. Brogger's article on "Pioneer Observational Internal" of 4/2/2000 and other articles dealing with ways to restore Pioneers, but I lack the guts (and the technical know-how) to open the little machine (I must confess I'm all thumbs when trying these tasks). Can anyone recommend someone (preferrably in the continental US) who'd be willing to take a look at my 27S and make her sing and dance again (though, in an algebraic gait still)? I sincerely appreciate any recommendations.

Re: Dead HP-27S
Message #8 Posted by Paul Brogger on 3 Apr 2001, 9:41 a.m.,
in response to message #7 by J. Lopez

I'm willing to offer my services, but I'm not sure at what terms.

I'm going on vacation for a couple of weeks. If by then you've not found a repair-person, email me and we'll see if something may be worked out.

Whatever happens, good luck with your baby!

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