HP 34C turning on but Error 0, zeros, frozen

[goncal]

I have owned a 34C since I was very kindly given it by my grandfather back in 1980. It was a prized possession back then and I have always looked after it well. It was the first programmable device I owned and I actually learnt to code with it.

After I got my 41C I put the 34C back in its case and box. I did remember to take the batteries out before putting it away thankfully.

The calculator survived several house moves and now belongs to my collection.

I took it out of its drawer a couple of weeks ago and purchased new batteries from Waterhosko on eBay:

https://www.ebay.com/itm/Hewlett-Packard...3312936986

However when I put the batteries on the calculator it would randomly not turn on, or alternatively show all zeros, or Errors 0 and 4, and appear to be frozen no matter what keys I pressed. (Actually when Error 0 came up the display would go blank after pressing any key)

I decided to take the calculator apart to look at the contacts. I used the great instructions in this article:

http://www.hpmuseum.org/cgi-sys/cgiwrap/...i?read=925

I must have been doing something wrong as it took me longer but did manage to open the case without breaking anything.

However there did not seem to be anything wrong. There was a bit of dust and some light brown goo on the board where the on-off and prgm-run switches are which I removed although I later realised this might have been contact grease applied by the Singapore assembly line staff on purpose.

I used a custom power supply set at exactly 2.4V to test the calculator before putting it back together and unfortunately all had been to no avail - same problem.

I would love to fix my beloved 34C but have as yet been unable to find any information on fixing this particular error.

Any help would be greatly appreciated.

PS Thought I would post a few photos. The light brown goo can be seen on the board contacts, it is now gone.

                   

[PANAMATIK]

(07-11-2018 09:20 AM)goncal Wrote:  I would love to fix my beloved 34C but have as yet been unable to find any information on fixing this particular error.

Any help would be greatly appreciated.

Error 0 and Error 4 without doing any key operations seems to be a defective ROM or processor. As you have a soldered version of this calculator, the usual contact problems of the solderless type cannot be the reason.

I will build a repair kit for the HP-34C until november of this year. It is based on the Woodstock LP circuit but fits into the HP-34C case. A prototype is already running. This would allow you to repair your beloved calculator if only the display is still OK.

Bernhard

[goncal]

(07-11-2018 03:29 PM)PANAMATIK Wrote:  

(07-11-2018 09:20 AM)goncal Wrote:  I would love to fix my beloved 34C but have as yet been unable to find any information on fixing this particular error.

Any help would be greatly appreciated.

Error 0 and Error 4 without doing any key operations seems to be a defective ROM or processor. As you have a soldered version of this calculator, the usual contact problems of the solderless type cannot be the reason.

I will build a repair kit for the HP-34C until november of this year. It is based on the Woodstock LP circuit but fits into the HP-34C case. A prototype is already running. This would allow you to repair your beloved calculator if only the display is still OK.

Bernhard

That would be fantastic Bernhard. I had already been looking at your Woodstock kit which of course I cannot use. Thank you.

[jebem]

From the published pictures, I see signs of battery leakage on the battery contacts, including the two PCB pins where the external charger is connected.

Assuming that you did not applied energy to the calculator using the external charger while having defective or absent batteries installed (that action can cause damage to the calculator as the charger is not a regulated power adapter), then I would use a ohmmeter to check for zero ohms (0.0 to 0.1 ohm max.) between the battery contacts and the PCB power supply side.

Or on a positive way, apply 2.4V to the battery contacts and use a voltmeter to read the voltage at the PCB power supply to be sure no voltage drop is occurring.

As the plastic flat cable copper traces are crimped/riveted to the battery contacts, there is a chance of bad continuity there.

When in doubt, and for testing purposes, I would use thin wires soldered between the battery contacts and the power supply, to make sure the calculator is getting the correct power voltage.

Note:
I would not apply heat or solder to the battery contacts rivets, as this will destroy the electrical contact and may even melt the plastic flat cable, making things worse.
If a bad contact is found, the quick and dirt fix is to use thin wire (wire wrapping wire) soldered to the battery contact.
A more professional, time consuming, and risky method would require to remove the metal rivet, clean, and apply a new rivet.

[goncal]

(07-11-2018 04:27 PM)jebem Wrote:  From the published pictures, I see signs of battery leakage on the battery contacts, including the two PCB pins where the external charger is connected.

Assuming that you did not applied energy to the calculator using the external charger while having defective or absent batteries installed (that action can cause damage to the calculator as the charger is not a regulated power adapter), then I would use a ohmmeter to check for zero ohms (0.0 to 0.1 ohm max.) between the battery contacts and the PCB power supply side.

Or on a positive way, apply 2.4V to the battery contacts and use a voltmeter to read the voltage at the PCB power supply to be sure no voltage drop is occurring.

As the plastic flat cable copper traces are crimped/riveted to the battery contacts, there is a chance of bad continuity there.

When in doubt, and for testing purposes, I would use thin wires soldered between the battery contacts and the power supply, to make sure the calculator is getting the correct power voltage.

Note:
I would not apply heat or solder to the battery contacts rivets, as this will destroy the electrical contact and may even melt the plastic flat cable, making things worse.
If a bad contact is found, the quick and dirt fix is to use thin wire (wire wrapping wire) soldered to the battery contact.
A more professional, time consuming, and risky method would require to remove the metal rivet, clean, and apply a new rivet.

Thank you very much for the insight. I cleaned the contacts and they were fine.

I should have reported that with the custom power supply connected through crocodile clips and a full set of zeros on the screen I tried gradually lowering voltage down from 2.4V.

Around 2.2V the 'low battery' dot on the left of the screen would gradually light up, then as the voltage decreased it would go out and the whole display (still filled with zeros) would dim. Further on that the zeros would turn into little flashing lights.

I tried this a few times with the same results unfortunately.

I fear I might have damaged the unit a few years ago when I tried to power it on with a faulty battery pack and the AC adaptor connected. Nothing happened and I just put it back thinking one day I would look for a new set of batteries.