HP67 doesn't turn on without battery pack?


Hi there,

I have this HP67 I recently restored by changing the gummy wheel. The battery pack leaked acid, so I removed it.

I also have the original HP main charger.

The calculator won't turn on using the main charger.

Does she require the battery pack to turn on correctly?

It seem working by feeding the calc with a 4.5V source from the battery pack contacts.

Thank you all,

Gabriele Zaverio
Freaknet Computer Museum
asbesto (at) gmail (dot) c0m

Edited: 6 Nov 2009, 1:15 p.m.


Hi, Gabriele;

in most HP calculators, the battery pack acts like a voltage reference for the power supply, so it is not recommended to power the calculator circuits without it. Anyway, if you did not succeed to make the HP67 to work with only the main charger but it works fine with a 4.5Vcc source directly, chances are you have either a bad main charger or a problem with the charger circuit inside the calculator.

Can you test the main charger to see if there is measurable voltage output? The value you should obtain is printed on it, in the same face you have the input AC connectors.


Luiz (Brazil)


Thank you for your answer!

I measure the voltage at the battery contacts inside the HP67; with the calculator OFF, I have about 5.5 Volt, and when I turn on the calculator, I have about 6.5-7 Volt. Very weird! :)


Hi, Gabriele;

that´s the reason you should not use the charger without the batteries, the voltage raises to a value that is far superior than the regulated value the circuits need to work. This happens because there is no voltage reference from the batteries, and the current source increases its output voltage to a peak level if no current circulates in the circuit load (in this case, the batteries being charged). I was interested on knowing the output value of the charger without connecting it to the calculator to see if it was working. Based on your measurements, I believe it is working, but I would ask you again to measure its voltage output without charge. Remember that it has a low voltage AC output, not DC. Next you should have a way to regulate the voltage in the battery compartment, and a single ZENER DIODE IS NOT SUITABLE for the job. I am not even sure if you can momentarily test the charger with the calculator by using a zener diode (4V7), we should wait for some extra information from other, more experienced guys who have already repaired HP67 calculators. I do not have one my own, just have repaired one some years ago, and the problem was in the card reader (adjustments and gummy wheel replacement).


Luiz (Brazil)

Edited: 6 Nov 2009, 3:51 p.m.


You should NEVER hook up your HP-67 to the power supply without a battery pack inside. It gives too much voltage (or current?) to the card reader circuit and can cause significant damage.

I'm not sure how to test the transformer without doing so, but please don't plug it in to the calculator without a battery pack.

There are good sources of aftermarket batteries at that auction site. Start there.


Thank you all, I will rebuild a fresh battery pack using 3 Ni-MH 1.5V batteries, they fit perfectly inside the old battery pack shell. :)


Hi, Gabriele;

the NiMH batteries are usually rated 1.2Vcc instead of 1.5Vcc and the regular pack for this model is actually three NiCad cells (because of the charger characteristics), with a working voltage closer to 3.6 Vcc, which is the best choice. I built a pack from a cell phone rechargeable pack for my HP55, which uses the same type of the HP67. Their internal power circuits are very different, though.


Luiz (Brazil)


I have read this thread and there are some confusing and I think incorrect assertions being made, so I'd like to try and clarify my own understandings:

1) The AC adapter/charger is a dual circuit combination adapter and battery charger that outputs DC on both circuits, not AC. The no load output of a properly functioning unit is approximately 17 Vdc on the battery charger side and 5 Vdc on the adapter side. You can check this by placing the unit in a live AC outlet, the negative (-) probe of your voltmeter in the center pole (-) of the plug and the positive (+) in the outer poles. The outer pole marked + should be ~17 Vdc and the unmarked pole should be ~5 Vdc. If any of these outputs are nil or significantly different values, then there is a problem with the AC adapter/charger. Many times the problem is in the cord and not the unit itself.

2) When the AC adapter/charger is plugged into the calculator, it depresses the bridge contact in the receptacle which opens the circuit from the battery to the main calculator circuitry (ICs, display, keyboard), such that the battery will no longer provide power to the calculator and is no longer a part of the circuit. At this point the calculator is receiving its power exclusively from the AC adapter (5 Vdc) circuit, and if the adapter is faulty or not plugged into a live wall outlet, the calculator will not work. This does not apply to the card reader, however, since it's on a separate circuit that is receiving power from both the battery and the charger side (17 Vdc) of the external power unit. So, it is quite safe to operate the basic calculator from the AC adapter/charger with the battery removed, provided you do not attempt to operate the card reader.

3) If the AC adapter/charger checks out OK, then you could have left a wire disconnected or reconnected incorrectly when you re-assembled the calculator. The HP-67 has some internal wires that are not soldered, but are plugged into receptacles and can easily come loose during disassembly.

I hope this helps and I have not mis-stated anything here.



Hi, Michael;

I have no HP67, but I have an HP55. I failed to consult the related documentation prior to answer the initial post because I was affraid the HP67 was dammaged if used without batteries. I also do not know if the HP55 can be used without batteries because it has a separated DC, regulated line, and the manual does not mention such possibility.

Now for the question: do both the HP67 and the HP55 share the same charging circuitry? If so, I was wrong considering the H67 was closer to the HP97 than to the HP55.


Luiz (Brazil)

Edited: 7 Nov 2009, 10:12 a.m.


I checked my HP charger: with the ground on the center pin, the Voltage measured to the other poles is ... 0 V !!!

And measuring between the external poles I have about 8Vcc.

Very weird! :(

I mounted new batteries into the HP67, it works very well :D

Now I think I have to fix my charger. A nice surprise: I don't need to "crack open" the charger, there are 4 easy screws! It opens very well. Very simple circuit!

Also, under the charger I can read an interesting notice. Here's what is written:

(there's a switch to select 110/220V)
INPUT - 86 to 127V - 48-66 Hertz
INPUT - 172 to 254V - 5VA



50mA 4.2V
4V 150mA


I will make and publish some detailed pictures of this charger very soon.

ps: checked with my tester, the center cable is interrupted. :)

Edited: 7 Nov 2009, 10:51 a.m.


Hi, Gabriele;

Data you wrote about your charger is:

(there's a switch to select 110/220V)
INPUT - 86 to 127V - 48-66 Hertz
INPUT - 172 to 254V - 5VA



50mA 4.2V
4V 150mA


Right? The one I have for my HP55 is the HP82002A, it is not the same as yours. Anyway, finding a faulty (interrupted) cable is the very beginning... If you consider that the faulty cable is the common, that that´s OK to measure 0Volts with the other poles. And the 8Vcc you measure between poles is closer to what you could have, it seems not to be OK. The HP82002A connected to a 220Vac outlet, without any load in the output, measures 5.2Vcc (regulated) and 15.2Vcc (unregulated) related to the central pole, and ~10Vcc (9.98Vcc) between poles, which is the difference between them.


Luiz (Brazil)

Edited: 7 Nov 2009, 3:17 p.m.


Hi Luis,

I have copied the following information from the MoHPC:

Classics (HP-35, 45, 55, 65, 67, 80)
Battery HP 82001B, Chargers HP 00035-60008, HP 03502A, HP 82001A/B, HP 82002A/B/C, HP 82010A (120/240 VAC), HP 82022A(240 VAC), HP 82011A (240 VAC)

Topcat (HP-91, 92, 95C, 97, 97S)
Battery HP 82033A, Chargers HP 82040A, HP 82059A/B/C/D, (HP 82032, 82066B, 82068B 240 VAC only)

As you can see the HP-67 and HP-55 use the same type of external power unit, as I have described. Since the HP-55 does not have card reader circuitry, it is safe to operate it off the external adapter without there being a battery inside. However, as stated by Randy, damaged is possible to the card reader circuitry, even if it is not operating.

The HP-97 uses a totally different power unit, which outputs ~12 Vac no load on a single circuit (it is rated 8 Vac, 3W). This is a similar situation to Spices and Woodstocks, where power signal rectification and regulation occurs inside the calculator and which require that a good battery be present when operating the calculator. Basically, this type of power unit should be used as a battery charger only, and should not be considered an external adapter for operating the calculator in lieu of batteries. In fact the Owner's Handbook for the HP-97 states that "Even though you are using the adapter/charger, the batteries must remain in the calculator whenever the calculator is used - Note: Attempting to operate the HP-97 from the ac line with the battery pack removed may result in wrong or improper displays."



1) Yes, a bad cord is very common followed by a bad 400uf filter cap.

2) It is *NOT* safe to operate a 65 or 67 from the AC adapter without a good battery in place. The battery is the only load on the constant current supply such that without the battery, you have 16 volts open circuit exactly as mentioned. But, there is a danger to the card reader sense amplifier/motor controller - as it is connected directly to the battery terminal and therefore sees that 16 volt source when there is no battery in place.

The original IC, 1826-0158 was used in the 65 and was susceptible to over-voltage damage. The part was redesigned as the 1826-0322 which appeared in the 67,97 and 41 readers. While it was supposedly better able to withstand the over-voltage stress, I wouldn't tempt fate.

Thanks to Tony Duell for explaining this quite clearly several years ago as it isn't obvious without seeing the schematics.

3) Not all 67's have the wire sockets, early units where soldered.

The 82002 Classic charger was well documented by Tony, details are available here


Thank you everybody!

Now I'm using my HP-67 with three fresh AA batteries :) It's working very well. I will search now for an user manual :)

p.s. Does someone know a way to build magnetic strip cards, maybe reusing old telephone magnetic cards?


I don't know how to built yor own magnetic cards but since the 67 uses the same type of cards as the 41, you can find them on the famous action site.


Thanks for those more complete answers.

I wanted to post the warning as soon as I could, and I wasn't aware of all the specifics.

We appreciate the work you (Randy, Tony and others) do to keep us well informed about these technical questions.


Randy et. al. can correct me on this, but I would hesitate using 3 new alkaline batteries in a NiCd designed machine.

The 67 is up to 35 years old as are the voltage regulating circuits. I don't know if it makes a difference but 3 alkalines new at 1.6 each equals 4.8 volts whereas 3 NiCd at 1.22 volts each equals 3.66 volts.

Does this impact on the circuitry, which granted, probably has a fudge factor built in.

It would seem to me to be a better idea to purchase 3 NiCd and charge them externally then to place 3 alkalines in their place.

Also, I hope you don't intend to use the charger while the 3 alkalines are in place!

Cheers, Geoff

P.S. the 67 is a Woodstock electronically in a classic case. However the charging side does not suffer the same catastrophic failure when the battery pack is bad or not in place as the 20 series does (HP-21...) As you found out, it would not run the card reader but does run the calculator for reasons explained above.


Geoff, the adapter outputs 5v dc directly to the circuits. So 4.5 to 4.8V from a pack of alcalines shouldn't be a problem.


Thanks Marcus,

I also restore vintage watches and one of the types I have repaired are the old tuning fork watches (ACCUTRONS) by Bulova.

The original movements (214) were designed for mercury 1.33 volts and when replaced by the 1.55 Silver oxides the tuning fork can run at higher frequency which is not controllable by the fast slow mechanism.

Different system I know, but still the voltage is critical.

Cheers, Geoff


Geoff, I agree. But the 67 is actually run at the higher voltage by the wall wart. So I think it's no problem.


I don't know how scientific this is, but I know this debate has been going on for at least 8 years on the Forum, especially when it comes to AA Lithium batteries, which can run at even a bit higher voltage than the alkalines.

Nobody here has ever reported a failure that they thought was due to using primary cells in these calculators (that I know of-- PLEASE correct me if I'm wrong).

My guess is that time causes more circuit failures than battery voltage... in fact, the components that seem to fail the most (other than chips getting fried by bad charging circuits) are capacitors, which I believe work better over time when "excercised". I'd still rather have cells with (so far) little or no potential to leak than worry about the much rarer risk of over-voltage.

That's just my opinion on this matter, but it's one based on lots of years of experience with these wonderful antiques.


Some time back I performed a overvoltage test on one of my many HP-45s to see what effect extended operation at 150% of its rated operating voltage (3.75 Vdc) might have on its circuitry. So, I hooked it up to my test bench regulated DC power supply, cranked it up to 5.6 Vdc, turned the calc ON, and left it running with -8888888888.-88 in the display for 7 days. The result of this particular test was that there were no observed failures. Now, I realize that this one sample test does not prove that operation at this level might not increase the chance of failure, however, it suggests to me that there is a significant margin of safety in the design, and that HP would not use an external adapter that outputs over 5 Vdc (no load) if that value was close to the safe limit for any components. Note that the 3.75 Vdc value is actually the minimum voltage at which the calculator will operate properly, and that a charged NiCad battery pack will exhibit a no load voltage well above that value.

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