Repair of HP-34C - Error 0 and Error 9

Hi everyone,

A couple of years ago I managed to acquire an HP-34C in excellent condition. I may have slightly overpaid for it, but I had wanted one for a long time to complete my modest collection and have enjoyed it very much, despite the relatively rapid battery drain while shut off compared to the 32E and 33E, likely due to continuous memory.

Recently, I brought it to the office and as I turned it on, the battery was again drained so I plugged it in - but had not turned it off before doing so and it behaved erratically and returned alternating Error 0 or Error 9, or Pr Error. It will 'sometimes' come up normally and will perform functions but after several seconds the LEDs flash and it reverts to a decimal point.

Could the circuit card have been damaged by plugging it in while turned on (I know, stupid mistake), and can it be easily repaired? I know there are a couple of choices for repair (Randy at FixThatCalc and Bruce at Vintage Calculator Repair) but have not pursued these options yet until I know more about the cause. I would like to try to fix it myself with help from a local electronics engineer if possible and I know how to safely open the unit and access the circuit card based on these instructions Spice Repair and I have read this interesting post from 2005 HP 34C Needs Help but not yet obtained the schematics.

Does anyone have advice on the best course of action?


Jeff Kearns

Edited: 11 Oct 2013, 9:27 a.m.


If it is a non-soldered unit, I would expect the problem to be a connection failure in the logic. The problem here is there is no realistic way to trouble-shoot. My approach with these monsters would be to test the IC's in a known good test unit and once I know I have a good set of chips, solder them into place.

If it is a soldered unit, the power supply and the battery connections are the usual suspects. Corrosion and high resistance battery connection paths are the first place to look.

Overall, the problems tend to be simple electrical faults of a mechanical nature. Sounds silly to phrase it that way but don't make repair any more complicated than it needs to be. Having the schematic is nice but not required for 99% of the repairs to unsoldered units.


Randy - The serial number is 2045S37XYZ and it a 6 oz calculator so I presume also a soldered unit. Based on your advice, I tested it with another rechargeable battery pack and adjusted the contacts (which are clean) and it now works perfectly - again!

Thanks. You have saved me some unnecessary trouble.



6oz without batteries would be a non-soldered unit :-(

5oz is a soldered unit. They tend to have serial numbers that end with an asterisk.

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