HP-34C "PR error"



#14

Thank you in advance for helping me.

I have a hp-34C fully working but everytime i switch it on/off i get "PR error" and my program is erase. I clean the switch contacts and the calculator didn't switch off alone by itself anymore but i still get pr error when powering it on. What can cause this situation?

By the way, can someone gime me a tip for opening the case of this series : every time i open the case i pray that the case will resist the high pulling i give to separate the two shells (the bottom of the case is very hard to dissambled without a great great force).

Fred


#15

I had an HP-33C that had the same problem. It was caused when I replaced the power supply board (the board with the ribbon cable attached to the battery connectors) with one from an HP-38E. Apparently the power supply boards from the "E" series are not the same as the ones from the "C" series. No power was being supplied to the memory when the calculator is swithed off.

If your calculator does not have a power supply board borrowed from an "E" series calculator, I would suspect a bad component on the power supply board.


#16

Well, i replaced the battery connector and the ribbon with a 33E in good condition but not the board itself... Are the ribbon the same in a 34C and a 33E?


#17

As far as I know, the ribbon cables and battery connectors are the same.


#18

I had the same problem with a HP-34C. Two of the chips were in wrong position. If you tell me the position/ reference that they have probably I can help you.

Best Regards from Spain

Jon

#19

Frederic --

Here's one copy-'n'-paste link to a posting on the subject (I plan to make this into a single tech article with pictures, along with illustrations from Luiz Veiera).

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv009.cgi?read=22660

-- Karl


#20

See also Norm's notes on how to make it easier to open your Spice the next time once you get it open for the first time

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=361

Good luck!

#21

I realize that the calculator is able to keep a program for about 22 seconds on "off". More than that i get the "PR error"; less the program is intact. What can cause this issue?

Fred


#22

In the C models, power has to be delivered to the RAM even if the calc is OFF. In your calc, that seems not to be the case. Turning off has the same effect on your machine as removing the battery: A built-in capacitor preserves memory for 22 seconds, then the capacitor is empty and your memory is erased.

Im not familiar with the ciruitry in the spices, but you should look for a trace (on the PCB or the flex ribbon) that supplies power to one of the chips without being interrupted by the power switch. That trace could be broken or have a bad contact somewhere. In fact, it would have to be broken somewhere between the battery and the capacitor.

Just thinking out loud, of course...

Good luck, and keep us posted.
Regards, Victor


#23

Fred:

Let me insist. I had the same problem. I am quite sure the chips are in wrong position.

Jon


#24

I think that if the chips are in the wrong position the calc cannot work (don't turn ON or display garbage) or simply fry the chips.

The power converter connections of the HP-25 and HP-25C are different, there is a path to power up the RAM even if the calc is OFF. In any case that one swaps the power converter or flex ribbon of the 25 and 25C, I think that 25C will not have the continuous memory (at last ~20 seconds powered by the backup capacitor).

Just my $0.02...

Best regards,

Nelson


#25

All the wiring on the 8 pin chips are conencted in parallel, except the one for the RAM chip has a separate line to the battery power supply. The machine will work just fine if the chips are in the wrong places. If the RAM chip is wrong, it will not get battery backup power. Only the filter cap will power it (for a few seconds). This can also happen if the RAM chip in the correct place but not seated properly.


#26

I was thinking of "wrong" as "upside-down"... not one in the another's place... You're right, the upmost chip has the vcc connection to the battery and the other two doesn't (if I recall right from my HP-32E).

Thanks for the correction!

Best regards,

Nelson


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