Disassembly and Repair of the HP 82059B 41C Power Supply

[akpoff]

I recently took an 82059B power supply apart, broke it, and then repaired it.

Why take it apart? Perhaps idle curiosity. I had previously disassembled the supply for an HP 45 that was in really bad shape. I appreciated the easy disassembly. Knowing the 41C-series supplies are stupidly expensive, I took one apart to see what I'd be in for if one quit working.

Disassembly is way harder than it should be. The trick is heat and persistent, gentle prying starting from the corners. I started at the top-right corner as your looking at the supply from the HP-logo side. The adhesive does not give up easily. You can see from the picture below I chewed the edges up a bit.

Since the 41C series supplies are AC output I assumed they'd be simple, probably just a transformer, and replacing a bad one should be pretty easy. And that's what they are, just a transformer. However, in the process I broke one of the magnet wires from the secondary. To add insult to injury, I broke it a few millimeters from the winding.

Still, a good opportunity to practice my repair skills. Preparing magnet wire for soldering isn't as simple as stripping typical electrical wire. 1) The magnet wire is sub-30 gauge (or is that super-30?). 2) The wire isn't PVC coated, rather it's enamel. There are at least two schools of thought to stripping enamel. One school says sand it with really fine sand paper, the other schools goes for burning it off as part of the soldering process. I tried soldering. That's a no go. Sanding is much easier.

I cut a small piece of 1000-grit paper, folded it and put the wire in between the folds and worked it until most of the enamel was gone. The longer piece of wire was fairly easy to work, the smaller piece near the secondary winding was a bit harder. Once I had removed enough of the enamel I tinned both pieces and then rejoined them.

       

I'm happy to say the power supply works. I'm debating what to use to seal the two halves. At the moment they're held together with a rubber band.

In short, the 82059B can be opened and repaired. You might even be able to reuse the case if you can find a small enough step-down transformer. You might have to modify the internal retention bracket and fasten the new transformed with an adhesive. You could certainly re-use the cord. The 82059A looks so much like the 82059B I'd guess the process and results would be the same.

I also have the 82040A. That's the one you can see into due to the cooling construction. It has a much larger transformer. Other than that, I think it also would be the same.

Edit: Add picture of top half of case. See measurements post below for transformer dimensions.

Cheers,

--Aaron

[brouhaha]

(01-23-2023 02:04 AM)akpoff Wrote:  There are at least two schools of thought to stripping enamel. One school says sand it with really fine sand paper, the other schools goes for burning it off as part of the soldering process. I tried soldering. That's a no go. Sanding is much easier.

There are different "enamels" used on magnet wire, many of which aren't actually enamel. Some of them are designed for direct soldering without any stripping, and others are not. Sounds like you had the kind that is not.

Unless you're buying the magnet wire from a top tier supplier that gives you actual specifications they'll stand behind, there's no way to know which you're getting. They're not visually different.

Thanks for sharing the details of your 82059B experience! It was interesting to see the photo.

[Hiwi]

Hi,
opening the charger is in most cases simple, if you use a flat screwdriver and insert and leverage where the cable comes out and excactly on the opposite site. There is a little slot. I never had any problems and i repaired many chargers. The plastic is ABS, so you can glue them together with little amount of CA.

But before opening i would always test wether the cable is broken in the plug, a common problem for the early versions of the charger (HP-19 or HP-97). The material of the plug and the cable are much softer, so when you bend it to much or pull the plug out drawing the cable, the contacts may break.

You can prick a small needle into the cable and measure the AC voltage.

To repair the plug, open it with a sharp knife and resolder the contact. Use hot glue to close the plug.

Or in some cases you can make a new plug:
Some female Tamiya (RC suplies) plugs may fit the HP contacts and you can make a new plug with some soldered PCB material as a form and fill it out with hot glue. Take black hot glue or shrinking tube.

Some newer transformers have a thermal fuse, which can be interruppted due to overload. Please check this before replacing the transformer.

Ralf

[Hiwi]

Some hints about magwire:

Since I am a hamradio amateur I make often toroids for antennas and filters and i have to solder the magwires to e.g a PCB. Heating the wire up over 390 degrees (C) for about 10 s will burn any kind of enamel. It works very relaible. After burning, i clean the wire with aceton.

Usually tansformers are made with double coated enamel for security reasons, so keep this in mind, when you repair windings of a transformer or wind it completely new.

Ralf

[akpoff]

Since the power supply is still open it occurred to me that I could measure the transformer for future reference. Below are dimensions for both core and bobbin.

The calipers are accurate to 1/1000", which seems like overkill, but the core fits in the bracket rather snuggly. The bobbin has a bit more space around it, but not much. I'd round down to hundredths for core measurements if you must. If you cut the bracket out you'd pickup a bit of space at the expense of having to glue the transformer in place.

I converted inches to metric using the standard conversion value of 1" = 2.54 cm.

Core:
Length: 1.406" = 3.57 cm
Width: 0.529" = 1.34 cm
Height: 1.148" = 2.92 cm

Bobbin:
Length: 0.987" = 2.51 cm
Width: 1.135" = 2.88 cm
Height: 0.744" = 1.89 cm

I edited the first post to add a photo of the top half so you can see the plastic posts that protect the plug blades and cable.

Cheers,

--Aaron