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HP34C Repair
10-29-2018, 07:00 PM
Post: #1
HP34C Repair
Hi All,
I'm the proud owner of an HP-34C which was in pristine condition till last week. Unfortunately now for some reason, some keys are unresponsive, and the unit is responding erratically without working correctly. I've tried with a new set of batteries, but the issue is still there.
Does anyone know someone that repairs these units? I've been searching on the forum, and I've read negative feedback on "Bruce" from vintagecalculatorrepair. If someone can put me in the right direction, I would appreciate it.
Cheers,
Javier

P.S: I've also got some HP41's card readers that would benefit from a repair service.
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10-30-2018, 06:46 AM (This post was last modified: 11-08-2018 09:11 PM by burkhard.)
Post: #2
RE: HP34C Repair
(10-29-2018 07:00 PM)javico Wrote:  Hi All,
I'm the proud owner of an HP-34C which was in pristine condition till last week. Unfortunately now for some reason, some keys are unresponsive, and the unit is responding erratically without working correctly. I've tried with a new set of batteries, but the issue is still there.

The Spice series, including the 34C, tend to suffer from a common design problem. In its wisdom to be clever with manufacturing, HP did most of the Spice production without actually soldering the main chips to the board. They are merely held pressed in place. Over time (and these things are 40 years old) dust, dirt, crud, and oxidation gets on the contacts which compromises this bit of genius in ways that would never bother chips soldered on.

Occasionally my 34C acts a little nuts also. I don't particularly want to take it apart if I don't have to (that is supposed to be a little tricky on the Spices...haven't tried it yet. I have found though that if I told the display end in one hand and the other end in the other hand and then give it a little twist (not enough to risk breaking anything, just a bit of torque on the long axis), that "fixes it" for a week or so.

Something to consider and test, if you like.

HP *eventually* started soldering the chips in, but most of them (I think...) are made the other way, so plenty get a little flakey as they age. But don't we all?

Sorry, no idea on a good source for service.
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10-30-2018, 07:51 AM
Post: #3
RE: HP34C Repair
Also avoid using the original HP charger. The Spice series, like the Woodstock's before them, can be damaged if the charger is plugged in and the battery is missing, has a poor connection or are worn out and go open. Basically HP depended on the batteries to regulate the charging voltage and prevent it from going too high.
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10-30-2018, 10:55 AM (This post was last modified: 10-30-2018 10:59 AM by aurelio.)
Post: #4
RE: HP34C Repair
(10-29-2018 07:00 PM)javico Wrote:  Hi All,
I'm the proud owner of an HP-34C which was in pristine condition till last week. Unfortunately now for some reason, some keys are unresponsive, and the unit is responding erratically without working correctly. I've tried with a new set of batteries, but the issue is still there.
Does anyone know someone that repairs these units? I've been searching on the forum, and I've read negative feedback on "Bruce" from vintagecalculatorrepair. If someone can put me in the right direction, I would appreciate it.
Cheers,
Javier

P.S: I've also got some HP41's card readers that would benefit from a repair service.
Of course you have already looked eventually for the presence of any little corrosion, due to a batteries' leakage.
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11-08-2018, 05:38 PM
Post: #5
RE: HP34C Repair
Hi All,
Thanks for your comments. Yes, I checked for corrosion, and that was not the issue, and I think my unit is one of the soldered ones, as I believe, was manufactured in 1981.
As I was not really keen to open it as electronics is not part of my remit, I preferred to spend some more pounds in another brand new fully charged battery pack. And guess what...it's working again, just as before. These antiques can be so tricky sometimes; I now think chances are that the charger is not working as may not be regulating the voltage properly or something. Actually, the other battery pack should be fine as well as it was brand new, it must be almost depleted but unable to be charged by the faulty charger.

How can I check if the charger is defective? with a multimeter?

Cheers
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11-08-2018, 06:03 PM
Post: #6
RE: HP34C Repair
(11-08-2018 05:38 PM)javico Wrote:  How can I check if the charger is defective? with a multimeter?

Yeah, select AC volts (a range to accommodate 9VAC - say 20V etc on a manual range meter) , plug it in and stick your test leads on the contacts , you won’t necessarily get exactly 9V because you’re not loading it... so it will undoubtedly read slightly more than 9VAC
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11-11-2018, 03:36 PM
Post: #7
RE: HP34C Repair
(11-08-2018 06:03 PM)Zaphod Wrote:  
(11-08-2018 05:38 PM)javico Wrote:  How can I check if the charger is defective? with a multimeter?

Yeah, select AC volts (a range to accommodate 9VAC - say 20V etc on a manual range meter) , plug it in and stick your test leads on the contacts , you won’t necessarily get exactly 9V because you’re not loading it... so it will undoubtedly read slightly more than 9VAC

Thanks, Zaphod!! Yes, so I've got myself a multimeter on Amazon and followed your instructions. I'm reading 8.9VAC connecting the terminals, so I would assume the charger is OK?. What I don't understand is that I've got the HP82090B European charger which says "output 6VAC, 1.3 VA". Sorry for my ignorance, but why am I reading 8.8VAC if the adapter has an output of 6VAC?
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11-11-2018, 04:08 PM (This post was last modified: 11-11-2018 04:09 PM by Dieter.)
Post: #8
RE: HP34C Repair
(11-11-2018 03:36 PM)javico Wrote:  What I don't understand is that I've got the HP82090B European charger which says "output 6VAC, 1.3 VA". Sorry for my ignorance, but why am I reading 8.8VAC if the adapter has an output of 6VAC?

The 6 V rating is just a nominal value which is (more or less) the output voltage when the full load of 1,3 VA is applied, i.e. with a current of approx. 220 mA. On the other hand you are measuring the voltage with no load at all, i.e. you get the open circuit voltage. Since this is a very simple AC adapter without any voltage regulation the output is higher than the nominal rating. Only a regulated power supply would deliver the same voltage for any load.

All this also happens with other AC adapters (these are not chargers, the charging circuitry is in the calculator). For instance the 82066A has a nomimal rating of 8 V~ but the open circuit voltage is close to 12 V. That's almost 50% more than the nominal value, just as in your case.

Dieter
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11-11-2018, 04:55 PM
Post: #9
RE: HP34C Repair
Recently, I restored a non-functional HP-34C to the working condition. It's a press fit version. After complete disassembly, I cleaned the contacts of PCBs and ICs with isopropyl alcohol. Prior to assembly, I slightly bent the legs of the ICs to increase the contact pressure. The calculator is working like new again.
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04-05-2021, 03:37 AM
Post: #10
RE: HP34C Repair
I can verify the "slight bend to the Pins" works to repair intermittent faults on my HP34c (now for sale on Ebay).
Also comment please
1.The inside of the HP34C also has what appears to be a DC-DC converter (coil transformer, transistor, diodes, resistors capacitors so i am wondering if the 9 Vac input is actually regulated down to 3v to charge and run the microprocessor?
2. I have noticed that AA alkaline cells are every so slightly longer than the original NiCads and cause compression damage to the contacts and the plastic battery compartment cracks. My thought is NOT to use AA alkaline cells ever but use Nicad or maybe NiMh cells exclusively.

Barry Moore retired elec. engineer HP Prime, Hp 40, Hp 35S, Hp15c, HP12c, HP34c
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04-05-2021, 04:05 AM (This post was last modified: 04-05-2021 04:08 AM by rprosperi.)
Post: #11
RE: HP34C Repair
(04-05-2021 03:37 AM)barry2718 Wrote:  2. I have noticed that AA alkaline cells are every so slightly longer than the original NiCads and cause compression damage to the contacts and the plastic battery compartment cracks. My thought is NOT to use AA alkaline cells ever but use Nicad or maybe NiMh cells exclusively.

This is correct, you should not ever use regular alkaline cells, the button on top adds to the length and will break the spring contacts (if not on first or second insertion, it will eventually). You should only use a pack made with flat-top NiCD or NiMH cells. Spring foam on the bottom of the pack will keep the pack tight without damaging the contacts. Also, using such cells makes it easy to charge them outside the machine, don't risk frying your ACT by charging them in the Spice.

--Bob Prosperi
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04-05-2021, 07:53 AM
Post: #12
RE: HP34C Repair
(04-05-2021 03:37 AM)barry2718 Wrote:  1.The inside of the HP34C also has what appears to be a DC-DC converter (coil transformer, transistor, diodes, resistors capacitors so i am wondering if the 9 Vac input is actually regulated down to 3v to charge and run the microprocessor?

From the Owner's Handbook - page 270:
"Note: Do not attempt to operate the calculator from an ac
line with the battery pack removed."

I think this explains everything
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04-08-2021, 07:59 AM
Post: #13
RE: HP34C Repair
(04-05-2021 04:05 AM)rprosperi Wrote:  
(04-05-2021 03:37 AM)barry2718 Wrote:  2. I have noticed that AA alkaline cells are every so slightly longer than the original NiCads and cause compression damage to the contacts and the plastic battery compartment cracks. My thought is NOT to use AA alkaline cells ever but use Nicad or maybe NiMh cells exclusively.

This is correct, you should not ever use regular alkaline cells, the button on top adds to the length and will break the spring contacts (if not on first or second insertion, it will eventually). You should only use a pack made with flat-top NiCD or NiMH cells. Spring foam on the bottom of the pack will keep the pack tight without damaging the contacts. Also, using such cells makes it easy to charge them outside the machine, don't risk frying your ACT by charging them in the Spice.
Thank you Barry

Barry Moore retired elec. engineer HP Prime, Hp 40, Hp 35S, Hp15c, HP12c, HP34c
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04-08-2021, 08:01 AM
Post: #14
RE: HP34C Repair
(04-05-2021 07:53 AM)AndiGer Wrote:  
(04-05-2021 03:37 AM)barry2718 Wrote:  1.The inside of the HP34C also has what appears to be a DC-DC converter (coil transformer, transistor, diodes, resistors capacitors so i am wondering if the 9 Vac input is actually regulated down to 3v to charge and run the microprocessor?

From the Owner's Handbook - page 270:
"Note: Do not attempt to operate the calculator from an ac
line with the battery pack removed."

I think this explains everything
Thank you for this advice, Barry

Barry Moore retired elec. engineer HP Prime, Hp 40, Hp 35S, Hp15c, HP12c, HP34c
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