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Opening a Woodstock external charger? - Printable Version

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Opening a Woodstock external charger? - John Garza - 11-02-2009

Does anyone have experience opening the woodstock series external charger (sometimes called a "reserve power pack")?

The thing is built into an attractive mini-woodstock case. But there are no screws on it (I checked under the rubber feet). I'd hate to pry it apart by force and crack the plastic.


I'd like to know as well. >> - tim m. - 11-02-2009

I have a classic series charger (03502A) that is sealed with no screws. I'd like to open it so that I may repair the strain relief and check the electronics. The constant-voltage supply reads 6.7 V no load; this seems a bit high, although my 35 chargers and functions fine off of the supply.


Re: Opening a Woodstock external charger? - Randy - 11-02-2009

Like most HP calculator assemblies, it was ultrasonically welded. You're right, it will most likely crack if you attempt to part the pieces.

Nothing inside but a diode, resistor and LED. *Very* hi-tech ;^)

Re: I'd like to know as well. >> - Randy - 11-02-2009

The sealed, smaller chargers were ultrasonically welded as well. The circuity is totally different than the 82001 and the higher voltage is normal. Trying to open one will usually result in breakage... since the weld lines are not exposed.

Thanks! >> - tim m. - 11-02-2009

I didn't realize that the circuitry was different. Am I correct in assuming that these sealed chargers were supplanted by the more common four-screw classic chargers?

It's also good to know that the higher voltage is correct. I'll see to repairing the strain relief from the outside.

Re: I'd like to know as well. >> - Charles Oxford - 11-02-2009

how do you check output voltage?

Re: I'd like to know as well. >> - tim m. - 11-02-2009

With the charger plug facing you, I measured between the center (common) and rightmost contacts. For a good picture, scroll about halfway down this page: http://www.jacques-laporte.org/HP35%20power%20unit.htm.

As for my HP-35 charger, some of the sealed plastic case is chipped away at the charger's strain relief. I used epoxy to fill in the missing parts. I also sliced a plastic strain relief off of an old in-line phono plug, cut it open, wrapped it around the charger cable where it emerges from the case, and secured it in place with more epoxy. This should reinforce the rather wimpy OEM strain relief.

Edited: 2 Nov 2009, 7:57 p.m.

Re: I'd like to know as well. >> - Charles Oxford - 11-02-2009

Thank you Tim


Re: Opening a Woodstock external charger? - John Garza - 11-03-2009

Just to clarify...

I'm NOT talking about the AC adapter that plugs into the wall.

This is basically a box to hold the batteries. You then plug the AC adapter into this box instead of the calculator. It looks like a 2/3 size woodstock case complete with rubber feet, "hewlett packard" metal strip, and an LED to indicate charging. It serves the same function as the more common classic series little black hinge-top "reserve power packs".

Not sure I made that clear enough in my original post.

I've been using alkalines for years in my woodstocks. Now I feel the urge to switch to rechargables. I'm well aware of the hazards of in-machine battery charging, so I thought this little jewel would do the trick. It certainly looks better than anything I could construct. Only problem is I think the diode is blown. When I connect my AC sdapter to it, the battery charging contacts show a little over 10 volts AC! I've never actually tried to use it until now. It's just been sitting in my "accessories box" with all the spare AC adapters, armored security cradles, field cases, etc. that I never really use.

-John (3665)

Re: Opening a Woodstock external charger? - Katie Wasserman - 11-03-2009

I happen to have a few of these and one was badly corroded and in need of repair. It had also been previously opened as there was a chip in the front. The two pieces of the shell are held together by what appears by glue around the boarder of the center rectangle. Here's a picture:

I think that it might be possible to break the glue bond without damaging the case, but it's not going to be easy.

The circuit is just a diode in series with what seems to be an 11 ohm 2 Watt resistor for charging and an LED in series with a 22 ohm resistor to indicate that current is flowing into the battery.


Edited: 3 Nov 2009, 2:00 a.m.