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My 82067B charger showed an intermittent fault at the battery connector after accidental crushing underfoot. Dismantling the connector revealed a broken diode(?) embedded in the rubber body.

Is this a Zener or what? Any ideas of characteristics and function?

Grateful for any advice to get 41C operating again: I have had this since new in 1980 and am lost without it!

The HP41 nicad battery pack and all the HP41 peripherals ran on the same charger (US model 82059). This charger is a simple AC output transformer with around 8VAC output. There was no diode, etc in the lead.

There are components in the charger plug of the topcat/HP41 charger. They're not well-known or documented, but the Portable Plus Technical manual mentions them -- it gives an example circuit for a car charger for that machine, gives a part number for the lead/plug (same cable as for the HP41, etc) and mentions the fact that it contains a pair of zener diodes in inverse series.

I don't know if it's 2 separate diode packages in inverse series or one component that acts like a bidirectional zener. The former would certainly work, though. I seem to remember they're something like 27V each (so they certainly don't do anything in normal use, just suppress transients), I will have to check.

Incidentally, that seems to be the difference between the -A and -B charges for the Woodstock and Spice series. The -B models have the zener diodes. In at least one series they're fitted inside the adapter case, not moulded inside the plug.

I once sliced open a bad HP-97 charger plug to fix a broken wire. Did not see any diodes in there, and I did some pretty major hacking on the thing. I eventually wound up cutting the plug off, making a wax mold, and cast a replacement. Looks like not all 82059's have diodes have diodes.

The broken mystery component was wired across the two leads from the transformer. It probably was about 4 mm long and 1mm diameter, opaque glass casing.

The transformer gives 13 VAC (on my meter), no load. Perhaps two Zener diodes in opposition (or a single bi-directional)could be used to smooth out and reduce this 13VAC to the rated 8 VAC marked on the case. If this is so, what value should they (it) have?

As an experiment I put 1W 7.5V Zener across the lead but it soon overheated and gave 6VAC output!

One of the Forum archive entries (1999?) mentions that the charger built into the battery pack operates from " a 12V rail ".

Finally, what is the Portable Plus manual?

Many thanks for your responses.

The transformer in this adapter (as in the other HP calculator chargers) has deliberately poor regulation, and appears to the load as having a relatively high (about 10 ohms from what I remember) internal resistance. It may well give 12V+ off-load (or with just a DVM connected), but this will drop when you connect it to a battery pack. A few years ago I connected various load resistors to each type of charger, measured the voltage and plotted the V-I curve. They were all very linear. I still have the data and the calculated values of the open-circuit voltage and internal resistance for various chargers. Let me know if you want this.

I do remember that the zener diodes in this, and in other HP chargers, were a much higher voltage than the transformer would ever give. I remember taking a spare charger lead and connecting it to my bench PSU (0-30V adjustable) with a resistor in series and measuring the zener voltage. I think it was about 27V. The zener therefore has no effect in normal operation, it is there to suppress high voltage transients only.

Finally, the Portable Plus was an HP Laptop computer, an enhanced HP110 (which was called the 'Portable'). It runs MS-DOS from ROM, but is not IBM compatible (neither at the hardware or BIOS level from what I remember). I have a couple, I also have the service manual and technical reference manual for it. It runs off an internal 6V lead-acid battery, but the plug-in charger is the same as the one for the HP41 (and topcats, HPIL peripherals, etc). The techref for that machine certainly mentions the zeners.

I will try a 27V bi-directional Zener in the cord and see if it will charge the battery pack outwith the calculator.

Thanks for the offer of the VI data but I do not think I would need them at this point. My main aim is to get the 41C back into operation soon.

Again, many thanks for the reponses.